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98 SPECIAL PUBLICATION No. 98
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Compilation Prakash Kumar Shrivastava, Amit Mandal, Pradeep Kumar and Amit Dharwadkar Editing Anil Joshi Manuscript Editing and Processing for Printing Arpita Pankaj, Sr. Geologist Publication and Information Division Central Headquarters Supervision Nirmal Dhar, Director, Publication and Information Division
Guidance G. P. Gupta, Deputy Director General, Mission-III B Overall Guidance Prabir Kumar Mandal, Additional Director General, Head Mission-III
Published by Director General, Geological Survey of India, 27, Jawaharlal Nehru Road, Kolkata-700016
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I am happy to note that the Polar Studies Division has come up with a compilation of the glaciological studies done in Antarctica in past thirty years. There could not have been a better timing for this than today when we are more concerned about the impact of the climate change than ever. Polar Regions offer an immense scope for understanding the cryosphere and the intricacy of the science of climate change. Geological Survey of India is associated with the Polar Research Programme since beginning and a specialized Division has been in existence since 1985 at Faridabad. The present compilation is an appropriate tribute to the geoscientists who have been participating in the Indian Antarctic Expeditions since beginning and have also taken up these studies to the Arctic Region. In addition to the Polar Regions, Geological Survey of India is also deeply involved with the glaciological studies in the Himalaya and I am sure that in near future a compilation on the comparative evaluation of the impact of climate change in these three distant cryospheric domains would be presented to us. I am hopeful that this compilation would be useful to the researchers and encourage the young minds to opt for a career in Polar Studies that offers a wonderful opportunity in research and adventure.
Harbans Singh Director General Geological Survey of India
PREFACE The Polar Regions have been the focus of glaciological studies owing to their sensitivity towards the global environmental and climatic changes. Geological Survey of India has been carrying out glaciological studies on the Polar Ice Sheet and the Ice shelf in the Schirmacher Region of the central Dronning Maud Land, East Antarctica for past three decades. The response of Polar Ice Sheet to climate change is being monitored since 1983 through continuous observations on the fluctuation of the Dakshin Gangotri (DG) Glacier snout. Since 2001, these measurements have been extended further to the entire ice front west of the snout. The accumulation or ablation of snow on ice shelf and polar ice sheet is being measured by three networks of 8, 20 and 16 stakes each, with first two being on the Ice Shelf and the third one on the Polar Ice Sheet. These measurements are being done annually on the exposed portion of the stakes. GPR surveys on polar ice as well as on ice shelf have been done to delineate land-ice-sea interface and for obtaining information about the basement configuration and depth profiles of the Antarctic lakes. GSI has also collaborated with other institutions on various other disciplines of the cryospheric research. Although the variability of climate can be observed on different time scales ranging from a year to a decade or millennia, the average conditions of thirty years are generally taken to delineate the patterns of change. The present compilation marks the three decades of glaciological studies in Antarctica by the GSI and may prove to be a milestone in the National endeavour to understand the science of climate change. Continuous studies of the DG Glacier snout has shown annual average recession of 0.57 m during the period 1983 to 1995, which increased to 1.59 m between 1996 and 2013. Since 1996 the glacier snout has receded by about 27 m and a cyclic pattern with high average annual recession after every 5 years has been recorded. Observations have also shown that the ice front west of the glacier snout has receded by 25 m during the period 2001 to 2013. Observations on the polar ice sheet stake network have shown that snow ablation starts with the onset of austral summer and is highest in December with gradual decline in January. Snow accumulation resumes with the onset of winter in February. The net annual accumulation on the Polar Ice Sheet has been observed to be less than half on the ice shelf. High annual recession for the DG Glacier snout and the western wall when viewed in terms of the net annual accumulation over Ice sheet and Ice shelf manifests a complex phenomenon that is affected not only by the local factors but also by the Antarctic circumpolar currents and the global thermohaline circulation. Initial inferences indicate that the ice free areas of the Schirmacher Oasis situated at a lower elevation are responsible for a higher positive radiation budget due to the presence of rocky outcrops in the surrounding region, resulting in more ablation compared to the main ice areas. In the later case, considering the snow accumulation over the Polar Ice Sheet to be normal, the higher accumulation over the ice shelf can be explained by its proximity to the sea that increases the availability of moisture and hence precipitation as snow. Painstaking efforts by the past and present contributors of GSI towards achieving this milestone are thankfully acknowledged. Critical review by the eminent glaciologist and fellow Antarctican Dr. Shardindu Mukerji had been of great help in improving the manuscript. The national Antarctic endeavour owes its success to the toil of participating officers of the multidisciplinary team being meticulously picked by the National Centre of Antarctic and Ocean Research (NCAOR), a statutory body under the Ministry of Earth Science, responsible for research in the Polar Regions and the Southern Ocean.
Dr. Anil Joshi Deputy Director General (Retd.) Mission-IV C
GLACIOLOGICAL STUDIES IN A PART OF EAST ANTARCTICA DURING THE LAST THREE DECADES
chirmacher Oasis got its name on 3rd February 1939 after the name of German pilot Richardheinrich Schirmacher. It is bound by East Antarctic Ice Sheet (EAIS) on the south and epi-shelf lakes and ice shelf (Fig. 1.2) in the north beyond which lies the Antarctic Ocean and Southern Ocean. The ENE-WSW trending Schirmacher Oasis is about 17 km long ice-free plateau with a maximum width of ~3 km (Fig. 1.1). With an area of 34 km², the Schirmacher Oasis ranks among the small Antarctic oases. It lies about 100 metres above mean sea level with mount Rebstriya (Trishul) forming the highest peak at 228m.
Fig. 1.1: Map showing locations of Schirmacher Range of East Antarctica and adjacent ice features.
The climate of the Schirmacher Oasis is relatively mild for Antarctic conditions. The annual average surface air temperature and the average annual wind speed have varied between -8.8°C to -11.1°C and 11.3 to 7.9 m/s for the period 1995 to 2013 respectively and the annual average precipitation as snowfall is 265 mm. During austral summer it gets about 350 hours of sunshine Novolazarevskaya station website data). The area is under continuous shower of Aurora Australis (Fig. 1.3).
Fig. 1.2: The northern edge of the range is characterized by presence of bays and epishelf lakes.
Fig. 1.3: Aurora Australis in the back ground of Maitri station.
Emperor and Adelie Penguins stay in the ice shelf north of Schirmacher Oasis. In the harsh winter season only Emperor Penguins continue on the continent. This area forms the habitat of some migratory birds like Skua, Antarctic Tern and Snow Petral (Fig. 1.4). Mosses, lichens and algae are common and survive by highest concentration of pigments and ability to dehydrate below -10° C. The Ice shelf area is free from floral occurrence.
Fig. 1.4 : Migratory bird like Skua, Antarctic Tern, Snow Petral and Adelie Penguin in the study area
1.2 Glacial Influence on the oasis Schirmacher Oasis represents a naturally exhumed terrain, reclaimed by the retreating ice sheet after the Last Glacial Maximum (LGM). It exhibits depositional and erosional landforms of the peri-glacial environment and is dotted with over than 100 ephemeral fresh water lakes. All major lakes of Schirmacher Oasis are located along the valleys which are modified by glaciers. Glubokoye (Long lake) (Fig. 1.5) and Zub (Priyadarshini) (Fig. 1.6) are two big landlocked lakes in this Oasis that have probably formed due to coalescing smaller lakes along deglaciated valleys.
Fig. 1.5: The lake Glubokoye (Long lake) and the highest elevation in Schirmacher Range, East Antarctica.
Fig. 1.6: Indian station "Maitri" on the bank of Lake Zub (Lake Priyadarshini), Schirmacher Range, East Antarctica.
Glacial terraces (Fig. 1.7), different types of moraines, patterned ground represent other depositional features whereas the glacial erosional features include roche moutonnees, striations (Fig. 1.8), glaciated valleys and terraces. Glacial valleys with two different trends are present with those extendeing ENE-WSW dissecting the NNE-SSW trending valleys at two places. Striations at different locations show a general trend of NNE-SSW indicating south to north movement of ice sheet on this oasis. Sudden change in the width of the oasis at two places, increase in topographic slope, changes in trends of striations represent the influence of episodic recession of ice sheet and tectonic activity. The presence of upto 3m high irregular ridge like ice forms from called 'Sastrugi' (Fig. 1.9) is a characteristic feature of this area that develops due to sculpturing of snow surface by wind erosion. Linear as well as curvilinear crevasses (Fig. 1.10) of variable dimensions are common in the area over the shelf ice and the polar ice sheet.
Fig. 1.7: Glacial terrace, Schirmacher Oasis, East Antarctica.
Fig. 1.8: Glacial striations on the country rock (garnet-biotite gneiss) of Schirmacher Oasis, East Antarctica.
Fig. 1.9: Sastrugi formed on the Ice shelf.
Fig. 1.10: Curvilinear concealed crevasses
During austral summers (December to February) snow melts and forms local circular ponds/pools whereas during the peak summer period water channels form. The melt water channels converge to "moulines" through which the melt water of the ice shelf drains to the sea. The melt water, the polar ice sheet, feeds the southernmost pro-glacial lakes, which overflow and feed the successive land-locked lakes situated at lower levels and finally drain in the epi-shelf lakes (Fig. 1.10), located at the junction between landmass and ice-shelf in the north. The seasonal snow and melt water flow is manifested as patterned ground. The subsurface as well as surface flow regimes eventually drain the entire Schirmacher Oasis in north on to the ice shelf and epi-shelf lakes (Ravindra et al., 2002). The epi-shelf lakes are connected to the ocean that lies beneath the ice shelf. Systematic classification of these lakes has indicated that the proglacial lakes, located along the southern periphery of the Oasis are fed directly by melting of the glacier. The land locked lakes usually occupy the deglaciated valleys and are recharged by melting of seasonal snow cover and melt water channels. The northern edge of the Oasis characterized by the presence of bays and epishelf lakes is frequently affected by tide water activity.
1.3 Hub of Science Study The Soviet Union set up its first research station Lazarev on the shelf ice in this region on March 10, 1959. It was reinstalled in 1961 into the Oasis and was named Novolazarevskaya. Afterwards on April 21, 1976, approximately two kilometres away from the Russian station Novolazarevskaya and about 120 m above sea level, the first German research station - Georg Forster - named after the German naturalist, was established in Antarctica. The station withdrew from service in February 1993 and by 1996 it was dismantled.
Fig. 1.11: The second Indian Research base 'Maitri' situated on Shirmacher Oasis, East Antarctica.
The Indian Antarctic Program was launched in 1981. The first research station Dakshin Gangotri was set up about 90 km from the Schirmacher Oasis on the shelf ice in 1983. It was decommissioned in 1989 due to excessive snow accumulation. In 1988, the Maitri Station was commissioned in the Schirmacher Oasis, and the first team wintered there is in 1989. Maitri is equipped with a meteorological station, geomagnetic and seismological observatories, and can accommodates up to 26 persons. It is located about 5 km west of the Russian station Novolazarevskaya. Maitri is connected to Cape Town, South Africa by Antarctic Logistic Company International (ALCI) flights, operating during the austral summer. The Antarctic coast is about 100 km north of Schirmacher Oasis and is accessible by ship from any part of the world. The area between coast and the Schirmacher Oasis is occupied by the ice shelf and can be negotiated by snow mobiles or by air through helicopters.
1.4 Glaciological Observations Glaciological observations in the Schirmacher Oasis were initiated by the Geological survey of India (GSI) in 1981 during the first Indian Antarctic Expedition. Dakshin Gangotri (DG) glacier was identified during second Indian Antarctic Expedition and since then it is being monitored regularly. Glaciological observations include measurements of DG glacier snout, its western flank and annual accumulation or ablation of snow on the ice shelf. Dakshin Gangotri glacier is situated in the western part of Schirmacher Oasis and its western flank extends up to the western extremity of the oasis. It can be approached on foot or by helicopter from Maitri. The stake network is established near the abandoned and now buried Dakshin Gangotri Station in ice shelf about 15 km inside from the coast.
Spectrum of Glaciological Studies
ntarctica provides a unique environment to study the interaction of glaciation and climate without much anthropogenic interference. Glaciological studies in Antarctica were initiated in 1981-82 during the first Indian Antarctic Expedition (Vohra, 1983). In the subsequent expeditions, some long term investigations were planned and the spectrum of glaciological studies was expanded to include fluctuation of polar continental ice margin, ablation and accumulation patterns on the ice shelf, monitoring of icebergs along the voyage route of Indian Antarctic Expeditions, variations in permafrost layers, dynamics of ice sheet and other parameters of climate change by analyzing ice cores raised from different locales representing specific geomorphic domains.
Fig. 2.1: Snout of Dakshin Gangotri (DG) glacier, Schirmacher Range.
2.1 Snout Monitoring As a part of monitoring the fluctuations in continental ice margin, a prominent glacial tongue named Dakshin Gangotri (DG) Glacier Snout (Fig. 2.1) was identified in western Schirmacher Range in 1983. The snout is monitored from fixed survey points on yearly basis and average annual recession rate for this glacier is calculated. In 1996 many peripheral points were added along this snout to enhance the scope of observations. The periphery of the glacier was also monitored every month during selective winters. Since 2001, the area of observations has been enlarged to cover the entire western extension (Fig. 2.2) of the Dakshin Gangotri glacier.
Fig. 2.2: Western extension of the snout of Dakshin Gangotri (DG) glacier on Schirmacher Range, known as Western Wall.
Fig. 2.3: Wooden stakes for measuring the snow accumulation / ablation
2.2 Snow Accumulation / Ablation Pattern The long term project of recording snow accumulation / ablation pattern on the ice shelf using fixed stake network (Fig. 2.3) was initiated during the second expedition (1982-83). Network farms containing 8, 16 and 20 stakes were fixed in a square grid fashion on ice shelf near India Bay region and monitored over a period of 25 years. Observations are made on yearly basis and on monthly basis during the selective winters.
2.3 Iceberg Monitoring The Antarctic ice sheet flows away from southern high altitudes, mainly under the influence of gravity, in almost radial fashion towards the ocean in north (Fig. 2.4). In the interior part of the continent, the ice velocity is very low and increases (about 2 km per annum) in the coastal areas. Once it reaches the ocean, a combination of various factors causes disintegration of the glacial ice and release of icebergs (Fig. 2.5). The icebergs observed in the Southern Ocean have formed by calving of ice shelves or glacier tongues floating into the sea (Fig 2.6). These icebergs carry large amount of fresh water away from the Antarctic continent. Monitoring of icebergs in Antarctica has been a part of glaciological programme of the GSI since the beginning of Indian Antarctic Expeditions in the year 1981. It is being done as per the guidelines of the Norwegian Polar Research Institute for keeping a world-wide watch on icebergs. The observations include recording the location, dimensions and morphological characteristics of the icebergs observed during the cruise. Besides their navigational significance, the data thus collected act as proxy information on the long-term changes in Southern Ocean environment. The iceberg positions within a radius of about 24 nautical miles are monitored along the navigational course by the ship's radar and other morphological features are observed through binoculars.
Fig 2.4: Flow pattern of Antarctic ice sheet showing direction of ice movement (source: Earth System Science, section 16).
Fig 2.5: Schematic diagram showing accumulation of snow, its movement, relative position of ice shelf and formation of icebergs.
Fig. 2.6: Massive Iceberg formed due to disintegration of the ice shelf
2.4 Permafrost Study Extremely low temperatures in polar region induce significant changes in various ground media. A comparative evaluation of the thermal changes in ice, fern and permafrost has been carried out. Annual variations in the thermal profile of permafrost were observed during selected expeditions. In another study, a small glacier was drilled through its entire thickness to the bedrock and thermal sensors were placed along the entire depth. Different parameters including the effect of the polar cold front, its maximum depth of penetration, response pattern within the layers of the glaciers, the average annual temperature within a depth of 10m and thermal inversion point within the glacier were studied for one complete year.
Fig. 2.7: Ground Penetrating Radar survey using 100 MHz antenna in bi-static mode.
2.5 Ground Penetrating Radar (GPR) Survey Ground-penetrating radar (GPR) survey (Fig. 2.7) is a non-invasive, time and cost effective, environmentally safe technique that is effectively used in the Polar Regions for subsurface mapping. During GPR data collection an-electromagnetic pulse (10-1000 MHz) is transmitted into the ground along a survey line. This pulse is reflected back to the surface from subsurface interfaces, which mark the contact of two mediums with different dielectric properties. GPR profiles were taken in a continuous stretch extending from the tip of Baalsrudfjellet Nunatak, where the rocks are exposed, to the edge of ice-shelf, covering a distance of about 78 km. Data generated through these profiles has been used to demarcate the boundaries between land-ice-sea. The continuous GPR profiles from continent edge to the present day sea shore (~78 km) have been useful in estimating the gradual changes in the thickness of ice sheet. Study has shown that the total volume of ice in this stretch is about 7240 cubic killometer and assuming a uniform density of 0.85 for the ice, it amounts to about 6154 cubic killometer of water.
Conducted during three successive expeditions in the year 2008 to 2011, the L-I-S interface has been inferred by these studies at 70°51'S: 12°14'E at a depth of 340 m below the surface along a north-south stretch east of Schirmacher Range. A 30m high convex structure was also detected north of the grounding line during this study. Ground Penetrating Radar (GPR) survey was carried out in the austral summer of 2011?12 during 31st Indian Scientific Expedition to Antarctica (ISEA) over Lake Untersee, central Dronning Maud Land (cDML). These studies formed a part of the multidisciplinary research being conducted by the TAWANI Group of Carl Sagan Centre, NASA, USA. Lake Untersee is specifically identified for studies owing to its uniquely alkaline character in contrast to the neutral to slightly acidic nature of rest of the lakes of Wohlthat Region. The present study is undertaken for understanding the nature of the physical layering in this perennially frozen lake. The vertical as well as lateral variations in the frozen surface of the lake are delineated through GPR profiles. The Data was collected using SIR 20 GPR system with 400 MHz antenna in a free run mode. The profiles reveal several prominent shallow interfaces up to a depth of about 30-35m.
2.6 Glacier Inventory Of Wohlthat Mountains The Wohlthat Mountain Range (9°-14°E Longitude & 71°10'-72°S Latitudes) located 110 km south of Schirmacher Oasis in Dronning Maud Land is a distinct physiographic unit in East Antarctica. This region, from south to north, can be divided into (i) polar ice plateau, (ii) the piedmont zone of polar ice sheet, (iii) the mountain barrier, dissected by outlet glaciers, and (iv) the ice shelf (Srivastava et al., 1988b). The Wohlthat Mountains show a conspicuous difference in relief between the southern and northern faces. In the Gruber and Petermann Ranges, the southern faces are about 600 m above the present ice surface and show periglacial effects. The northern face, on the contrary, exposes a mature alpine relief (2800 m above sea level). Horns and serrated ridges form characteristic features of Gruber and Petermann Ranges (Fig. 2.8). Studies of recessional moraines indicate that the deglaciation in the eastern part of Wohlthat Mountain has taken place in three stages leading to the formation of dry valleys. The presence of ice sheet at 2000 m above sea level is indicated by polished surfaces and striations. These striations imply northwesterly flow of the glaciers.
Fig. 2.8: Horns and ridges of Wohlthat mountains
The Wohlthat Mountains also forms a barrier to the northern flow of continental ice sheet and glaciers. The ice tongues emanating from the ice sheet in the form of outlet glaciers dissect Wohlthat Mountain chain into independent blocks. Each of these blocks supports an independent network of glaciers and exhibit different flow regimes. Norwegian topographical map (1:250,000) and Landsat imageries in band 4 and 7 along with some vertical/oblique aerial photographs were used as the base map for this inventory. A glacial inventory of the Wohlthat Mountains was prepared as per the guidelines of the Manual of Temporary Secreteriat (TTS) of World Glacier Inventory (Muller, 1977, 1978). The Wohlthat Mountains has been divided into four blocks as (i) Gruber, (ii) Petermann, (iii) Humboldt and (iv) Orvin. There are total 122 glaciers in Wohlthat mountain chain. Out of this, more than 50% of the glaciers are oriented in NW and W directions. Most of the glaciers are smaller than 1 sq km. In general the glacier elevation varies between 700 to 2600 m above sea level. The glaciers are of mountain glacier type occurring in the form of ice aprons or flowing in simple basin. The general elevation of outlet glacier ranges from 1900 metre above sea level (masl) in the north in the Gruber block. Within the ambit of glacierisation of Gruber, 19 glaciers of different orientation and dimension were identified. The general elevation of the outlet glacier is 2300 masl in the south to 1000 masl in the north in Petermann block. There are 45 glaciers in this group. In Humboldt group the general elevation of outlet glacier (and ice sheet) is 2100 masl in the south to 1000 masl in the north. There are 41 numbers of glaciers in this group. In the Orvin group there are 17 glaciers and the general elevation 2100m to 1700m from south to north (Srivastava et at., 1988a).
2.7 Study On Fast Ice A study on Fast Ice near India Bay region has shown that since April onwards, the firm base develops and gets connected to the shelf with a gradual slope in May (Singh et al., 1988). The hinge line between ice shelf and fast ice does not show any tensional and compressional cracks till the end of austral winter. The thickness of fast ice varies between 0.61m and 3.17m with average density, ranging between 0.4 and 0.65 gm/cc.
Fig. 2.8: Ice core drilling on ice shelf by electro-mechanical drill.
2.8 Collaborative Studies Antarctic ice sheet is an exceptional repository of the climatic record of the past. The proxy indicators are preserved within the icy layers as air bubbles, gases, pollen, dust, volcanic particles and pollutants. The initial attempts of ice core recovery were limited to the hand auger drill in the ice shelf area., Ice cores were raised along a transect between the ice shelf and polar ice sheet in a collaborative programme with National Centre for Antarctic and Ocean Research (NCAOR) and were analysed for drawing inferences on the palaeoclimatic history of the region. The motorised electromechanical drill (Fig. 2.8) was first used in 1993 and in subsequent years shallow ice core drilling up to a depth of 100 m was undertaken in few more expeditions (Chaturvedi and Asthana, 1996a, 1996b; Chaturvedi et al., 2001). Ice sheet dynamics with the help of global positioning system (GPS) has also been studied in a collaborative programme was with Indian Institute of Geomagnetism (IIG). Data was recorded for two successive austral summers on Polar ice sheet to the south of Schirmacher Oasis and used for interpreting annual movement patterns, velocity, direction and stress of the ice sheet.
Dakshin Gangotri Glacier
he Schirmacher Oasis extends in a WNW-ESE direction depicting an ice free terrain consisting of small hillocks and valleys. The Dakshin Gangotri (DG) Glacier (70°45.566'S & 11°34.614'E - 70°45.406'S & 11°34.289'E), lies in the western part of Schirmacher Oasis and forms a prominent glacial tongue of the East Antarctic Ice Sheet (Fig. 3.1) (Kaul et al., 1985a & b). The snout of this glacial tongue (Fig. 3.2) is being observed since 1983 for assessing the fluctuation of the polar ice margin in this part of Antarctica.
Fig. 3.1: Map showing locations of Dakshin Gangotri (DG) glacier and its western flank along with research stations in Schirmacher Oasis.
3.2 Methodology DG Glacier was being monitored from a fixed survey point since 1983. Another fixed reference point was added in 1993. With a view to further refine the observations, 19 more points were added along the periphery of the snout in 1996. Afterwards 18 more points were fixed in 2001 along the western flank of the glacier (Fig. 3.1). Every year, the position of snout and the western flank of this glacier are measured with reference to the fixed observation stations on ground to record the secular movement of the continental ice sheet overriding the Schirmacher Range. During the years 2003 and 2005 the movement of the ice sheet was also measured with GPS fixed on the ice surface further south of the study area. The meteorological data required for further elaboration of climatic control on the glacier is obtained from the website of the neighbouring Russian Station Novolazarevskaya and from Maitri station assuming that the climatic condition around these research stations and the DG Glacier, that is located about 5 km and 9 km west of it respectively are nearly the same.
3.3 Trends Observed The DG Glacier receded by 7 m during the period 1983-1993 (Asthana et al. 1996). The rate of average annual retreat varied widely during 1996 to 2014 (Table 3.1). Perusal of the uninterrupted annual recession data since 2 1996 shows that about 4800 m area has been vacated by the snout of Dakshin Gangotri Glacier between 1996 3 and 2011 due to disappearance of about 672 X 103 m of ice. After considering the length of total snout and its 3 western extension, it is estimated that about 576 X 103 m of water has been lost in this period. Taking the recession of snout and the western flank together into consideration, the total volume of water would be more than 10 times the above stated figure. Between 1996 and 2014 the glacier retreated at an average of 0.72 m per annum (Table 3.1.a and 3.1.b). It has been observed that, the western flank is showing both recession and advancement which is different to the recessional trend of the DG Glacier snout (Fig. 3.3 and 3.4). On an average, the western wall has shown four advancements between 2007 and 2014. Within the western wall, the eastern portion has retreated less than the western side.
Fig. 3.2: Observation points on the snout of DG glacier and their positions in 1996, 2001 and 2011.
Fig. 3.3: Retreat of the snout of Dakshin Gangotri glacier along different observation points
Fig. 3.4: Retreat of the western flank of Dakshin Gangotri glacier along different observation points.
3.4 Meteorological Parameters The meteorological data of past few years from Novolazarevskaya station shows fluctuations in average annual parameters like surface air temperature (Fig. 3.5), ground temperature (Fig. 3.5), wind speed, summer temperature and in winter temperature (Table 3.3). However, there had been a cyclic pattern in the precipitation rate in the earlier years (1996-2003). Between years 1996 and 2009, the snout of the Dakshin Gangotri (DG) glacier has shown that every major recession is preceded by higher average annual surface air temperature (Chaturvedi et al. 2009; Shrivastava et al. 2011). The same relationship has been observed with average annual ground temperature, average annual winter temperature and to some extent with average annual wind speed and average annual summer temperature. In order to understand this cyclic pattern of the recession of the DG glacier snout more observations in conjunction with additional meteorological parameters like albedo, El Nino etc. would be required in the coming years.
Fig. 3.5: Average annual fluctuation in Surface Air (SA) Temperature and Ground (G) Temperature as recorded at Novolazarevskaya station.
Fig. 3.6: Cyclic pattern of average annual recession of DG snout.
Figure 3.7: Average diurnal temperatures in Schirmacher oasis (Source IMD)
3.5 Glacial Parameters The average annual recession of the DG snout shows no correlation (Gupta and Kapoor, 2002) with average annual meteorological parameters including surface air temperature, ground temperature, maximum surface air temperature, relative humidity, precipitation, wind speed and total cloud cover of the same year (Table 3.4) but a better correlation with these data of previous year (Table 3.4). These observations indicate that meteorological parameters exert some control on the recessional pattern of the DG glacier with a time lag of one year. The topographic elevation, incident sunlight angle and duration are other influencing factors that require further investigations to ascertain the causative factors of the observed recession of DG glacier. However, a sense of cyclicity in the recession pattern of the glacier is observed (Fig. 3.6). During the period 1996-2013, the DG glacier showed major peaks of recession in every five years (1998, 2003, 2008 and 2013). For ascertaining a link between the factors responsible for recessional patterns in the DG Glacier snout and its western flank a graph of three hourly temperature variation during summer period in Schirmacher Oasis shows, that temperature gradually rises after 0600 hour GMT and attains maxima at around 1200 hour. After 1800 hour temperature declines and reached the lowest at around midnight (Fig. 3.7).
Fig. 3.8: E-W Topographic cross section of part of the Schirmacher Oasis along DG snout and the western wall (Shrivastava et al., 2011)
Thus, the western wall receives maximum solar radiation between 0600 hour and 1800 hour GMT during austral summer. A cross section across the snout and western wall (Fig. 3.8) reveals that DG glacier snout lies in a small valley portion whereas the western wall occupies higher elevation. This topographic setting allows lesser duration exposure of sun light to the glacier snout in comparison to the western flank. The temperature difference and topographic disposition thus seem to be the main causative factors for the difference in recessional behaviour of glacier and its western flank and greater ablation of western flank than the glacier snout (Fig. 3.3, 3.4). Similar trend is also noticed in Himalayan glaciers where north facing glaciers are reportedly healthier in comparison to south facing ice bodies as the latter receive more solar energy per year. Continuous monthly monitoring of DG glacier snout for five years (1995-2000) shows that most of the points show multiple advances and retreat cycles in a year. Mostly, the peaks of advance coincide with the culmination of winter in September-October when the glacial front advances to its maximum limits. There are many minor corresponding cycles of retreat, except those which coincide with breaking of the escarpment.
3.6 Data Interpretation The minor correlation between surface air temperature anomaly of Schirmacher region along with global (southern and northern hemisphere) temperature anomaly pattern provides space for some other factors such as effect of ocean current, albedo, isostacy and solar cycle, which may be contributing to the recession of this snout. Hence, the observations indicate very intricate relationship between recessions of DG glacier snout and with the meteorological parameters and needs further study by incorporating other parameters like southern ocean currents, El Nino Southern Oscillation, solar cycle and anthropogenic influence.
Table 3.1.a Recession of the Dakshin Gangotri (DG) glacier (in m) upto 2004-05 Serial No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Avg.
Obs. Pt. 1 2 2A 3 4 4-A 4-B 5 5-A 5-B 6 7 8 9 10 11 12 13 14A 14 15
Original 1996 200 450
199697 66 43
199798 69 247
100 200 200 250 700 110 110 150 150 500 200 400 200 350 100
28 -20 19 20 16 39 32 -14 22 9 149 10 9 151 84
62 103 41 25 94 2 63 44 138 131 101 33 157 114 141
72 191 48.74
188 169 101.16
1998- 1999- 2000- 2001- 200299 2000 01 02 03 -33 68 -14 -34 69 170 170 30 15 94 This point buried in ice fall. 30 13 36 41 60 57 32 29 34 31 25 25 36 44 37 5 40 34 31 38 60 60 -98 21 3 41 -42 49 31 79 55 40 4 41 63 16 12 84 118 96 74 40 91 85 214 -20 78 0 98 75 106 98 71 110 217 4 157 57 -2 173 5 75 74 -37 63 53 33 32 66 95 101 89 68 2 214 This point buried in ice fall. 196 196 132 66 332 103 102 57 66 340 55.16 67.68 40.63 41.89 120.68
2003- 200404 05 89 301 175 171 50 67 18 -10 319 -1 29 191 130 -71 -51 13 84 94 -13
66 30 20 -18 -10 27 2 158 151 115 91 60 -5 91 229
258 132 79.11
20 154 87.00
Table 3.1.b Recession of the Dakshin Gangotri (DG) glacier (in m) upto 2013-14 Serial No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Avg.
ObsPt. 1 2 2A 3 4 4-A 4-B 5 5-A 5-B 6 7 8 9 10 11 12 13 14A 14 15
Original 1996 200 450 100 200 200 250 700 110 110 150 150 500 200 400 200 350 100 150 650
2005- 2006- 2007200806 07 08 09 14 10 357 43 21 -136 335 -98 This point buried in ice fall. 58 128 39 18 66 23 28 12 18 41 39 21 112 -7 43 4 -35 18 -40 334 75 -20 14 13 65 -49 108 3 243 57 280 35 150 45 120 123 37 83 74 13 151 7 47 34 66 49 74 138 21 144 62 14 55 81 221 77 116 120 171 84 This point buried in ice fall. 261 503 8 1094 130 48 111 122 85.47 60.26 110.05 109.68
2009- 2010- 2011- 2012- 201310 11 12 13 14 This point buried in ice fall. 8 37 -19 102 -24 44 21 21 25 78 -9 54 9 2 38 15 21 -2 37 52 16 75 39 47 55 10 120 44 -22 66 25 72 5 28 40 5 71 15 39 56 14 88 60 93 59 -42 230 20 -18 38 90 80 73 0 14 -28 79 -15 153 53 46 26 -10 342 ---18 -104 -120 71 91 21 -50 220 28 4 7 -267 161 32 125 46 620 187 67 65 103 2 86 171 87 73 214 238 131 26.00 80.63 33.00 92 29
Table 3.2 Recession of the Western flank of Dakshin Gangotri Glacier during 2001-2011 (in m). Fixed Point s XX 2
110 26.390 ’
XX 3 XX 4 XX 5 XX 6 XX 7 XX 8 XX 9 XX 10 XX 11 XX 12 XX 13 XX 14 XX 15 XX 16 XX 17
700 44.621’ 700 44.729’ 700 44.797’ 700 44.879’ 700 44.932’ 700 45.225’ 700 45.268’ 700 45.300’ 700 45.417’ 700 45.428’ 700 45.407’ 700 45.403’ 700 45.424’ 700 45.436’ 700 45.631’
110 26.529 ’ 110 27.660 ’ 110 28.147 ’ 110 28.562 ’ 110 28.905 ’ 110 31.120 ’ 110 31.401 ’ 110 31.614 ’ 110 33.135 ’ 110 33.289 ’ 110 33.478 ’ 110 33.619 ’ 110 33.733 ’ 110 34.022 ’ 110 34.739 ’
0.95 0.78 1.53 2.67 2.53 2.50 1.72 3.30 1.84 1.08 1.58 1.02 4.06 0.53 0.94
21.83 16.28 30 18.45 11.76 16.93 4.96 19.73 10.94 11.55 9.21 13.52 4.86 Not Available
22. 86 13. 44 13. 66 13. 78 20 6.1 21.8 13 15. 92 8.63 5.04 5.48 Not Available
21.05 14.75 27.33 15.92 9.26 15.21 1.66 17.89 9.86 9.97 8.19 9.46 4.33 Not Available
XX 18 2.87 Annual average recession (2010-2009) Annual A verage recession (2001-201 3)
22.08 11.91 10.99 11.25 17.5 4.38 18.5 11.16 14.84 7.05 0.98 4.95 Not Available 12.7 11.3
Table 3.3 Meteorological parameters (annual average) as recorded at Novolazarevskaya Station (source online data) AAR- average annual recession, AAST- average annual surface air temperature, AAGT- average annual ground temperature, MSAT- maximum surface air temperature, AARH- average annual relative humidity, AAP- average annual precipitation, AAWS- average annual wind speed, AATCC- average annual total cloud cover. Year
2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996
92 33 80.63 26 109.68 110.05 60.26 85.47 87 79.11 120.68 41.89 40.63 67.68 55.16 101.16 48.74
-9.8 -10.3 -9.6 -11.1 -10.2 -10.6 -9 -10.6 -10.1 -10.8 -9.9 -8.8 -10.3 -11 -10.3 -10.7 -10.1 -9.2
-8.1 -8.8 -7.8 -9.6 -8.5 -9.4 -7.3 -8.7 -8.1 -10.2 -7.8 -7.7 -8.7 -8.9 -8.1 -8.9 -9 -8.3
-7.1 -7.6 -6.9 -8.1 -7.3 -7.8 -6.5 -7.7 -7.3 -7.6 -7 -6.4 -7.7 -8.2 -7.6 -7.9 -7.4 -6.6
46.7 48.6 50.9 42.8 50.9 46.4 44.8 47.1 48.5 44.8 45.9 47.4 47.7 47.5 47.8 50.3 50.4 49.5
17.7 15.6 22.1 7.3 31.5 17.6 6.7 24.1 8.2 27 28.2 27.9 9.9 10 14.6 27.6 14.3
9.9 10.2 10.6 7.9 10.1 9.4 9.4 9.6 9.8 9.8 10.5 10.9 10.4 9.6 10.3 10 10.3 11.3
5.7 5.4 5.5 6.5 6 6.3 6.3 6.5 5.5 6.4 6.8 6.4 6.4 6.1 5.6 6.1
Table 3.4 Statistical correlation of recessional pattern of Dakshin Gangotri glacier with meteorological parameters (abbreviations as per table 3.3)
AASAT (°C) AAGT (°C) SMAT (°C) AARH (%) AAP (mm) AAWS (m/s) AATCC (tenths)
Correlation coefficient of AAR during same year
Correlation coefficient of AAR during preceding year
-0.1 0.03 0 0.3 -0.12 0.2 0.03
0.39 0.46 0.3 0.39 0.17 0.52 0.43
4.1 Introduction The ice shelf surrounding the Antarctic continent is dynamic owing to continuous supply of ice by glaciers and precipitation and wastage due to calving of icebergs as well as basal melting. Mass balance studies provide useful information on the status of various components of the cryosphere in the Polar Regions and a realistic assessment on the impact of climate change. Indian Station "Maitri" in the Schirmacher Range is ideally located for such studies on polar ice sheet and ice shelf (Fig. 4.1).
Fig. 4.1: Ice Shelf and an Iceberg near India Bay region, Princess Astrid coast, East Antarctica.
Systematic measurements on the ice shelf were started in 1985-86 during the fifth Indian Expedition by establishing a stake farm (Fig. 4.2) about 1 km ESE of Dakshin Gangotri Station (Singh et al., 1988). The annual net accumulation is measured using the exposed height of the stake over the ice surface. The stake farm lies in an accumulation zone (70°4'16.1"-70°4'35.4"S and 12°1'27"-12°2'31.6"E) and is being maintained by fixing additional stakes as required to ensure continuity in observations. In the earlier expeditions, the stakes were being monitored on fortnightly or monthly basis due to their proximity to the DG Station. After the station was abandoned, measurements are being made annually. Seasonal / monthly patterns of accumulation/ablation were studied during the austral winter of 1995-96. Discussions on the studies carried out during the last 18 years (1996 - 2014) have quantified the rate of snow accumulation and the average annual net accumulation on the ice shelf follows.
Fig 4.2: Fixed stake network over ice shelf.
4.2 Discussion Due to Long hours of sunlight during the polar summer (November to March), results in higher temperatures with maxima in January (Ravindra et al., 1994a, Singh and Kulandaivelu, 1994, and Koppar, 1995). This phenomenon results in higher humidity and initiates precipitation in coastal areas. Data on annual snow accumulation on ice shelf between 1996 to 2014 shows widely variable range (Table 4.1). The average annual accumulation of snow over ice shelf shows a cyclic pattern in every 5 to 6 years. When compared with the average annual surface air temperature of Schirmacher region (Fig. 4.3), snow accumulation over ice shelf shows correlation in the year 1996-97, 2001-02, 2003-04, 2006-07, 2007-08 and 2008-09, but still perfect correlation could not be established between them. Likewise, average annual wind speed also shows correlation with average annual snow accumulation in the years 1996-97, 2001-02, 2003-04, 2007-08 and 2008-09.
Average annual accumulation patterns appear to be non uniform (Fig 4.3). Plots of average annual temperature and wind speed (Table 4.1), (recorded at Novolazarevskaya station) shows that higher temperatures in the year 1996-97, 2001-02 and 2006-07 are marked by higher accumulation. Similarly, decrease in average annual surface air temperatures in year 1999-2000, 2003-04 and in 2007-08 are marked by less accumulation (Fig. 4.3). The average annual wind speed could not show correlation with snow accumulation except in the years 2001-02 and in 2008-09. The average snow accumulation or ablation (Table 4.1) has been calculated using data of all the exposed stakes during the period 1999-2014 (Fig. 4.2). The data so obtained is cumulated for the entire period, taking March 1996 as the base to determine the absolute accumulation or
Fig. 4.3: Average annual wind speed and snow accumulation / ablation on ice shelf.
the actual rise in the surface level of the ice shelf. The cumulative rise in the surface level of the ice-shelf has been plotted against time (year) on an X-Y scatter plot (Fig 4.4). The progressive rise in ice shelf is shown by second order polynomial best fit curve with R2=0.978 (measure of reliability) for the above mentioned period. The curve in (Fig. 4.4) highlights a cyclic pattern suggesting that the rate of growth is not uniform. It is apparent from the pattern that the periods of higher accumulation are followed by periods of lesser accumulation resulting in a non uniform growth of the ice shelf. Though the main cause of reduction in the total ice is formation of icebergs due to calving at the shelf edge (Fig. 4.5), the high variability in snow mass balance can also be attributed to ablation processes driven by katabatic winds. A few strong wind events can greatly decrease the mass through snowdrift sublimation, especially during the summer. This phenomenon can be visualized through the plots of average annual accumulation/ablation and wind Fig. 4.4: Cumulative plot of average accumulation / ablation of snow on ice shelf. speed. In addition, the drift snow plays an important role in altering the surface profile of the shelf ice (Mukerji et al., 1995).
Fig. 4.5: Calving of ice shelf in the India Bay Region, Princess Astrid coast. Table 4.1: Average annual wind speed, accumulation and cumulative accumulation of snow over ice shelf.
2013-14 2012-13 2011-12 2010-11 2009-10 2008-09 2007-08 2006-07 2005-06 2004-05 2003-04 2002-03 2001-02 2000-01 1999-2000 1998-99 1997-98 1996-97 1995-96 1994-95 1993-94
Avg. Surface Air Temp (C°)
Avg. Wind speed (m/s)
-9.8 -10.3 -9.6 -11.1 -10.2 -10.6 -9 -10.6
9.9 10.2 10.6 7.9 10.1 9.4 9.4 9.6
-10.1 -10.8 -9.9 -8.8 -10.3 -11 -10.3 -10.7 -10.1 -9.2 -10.3 -9.4
9.8 9.8 10.5 10.9 10.4 9.6 10.3 10 10.3 11.3 9.7 9.9
Annual Accum. (cm) 22.9 74.07 93.35 33.5 32.2 6.2 65.6 55.9 4.92 14.4 52.2 45.2 22.14 22.14 60 66.5 -
Cumulative accumulation 544.72 521.82 447.75 354.4 320.9 288.7 282.5 216.9 161 156.08 141.68 89.48 44.28 22.14 -
Icebergs-Observation and Classification
he importance of icebergs as bulk carriers of fresh water is known for quite some time. There have been proposals for towing the icebergs from various ice shelves of Antarctica to different destinations in order to address the water scarcity. The Antarctic ice sheet continuously flows down from southern high altitudes under the gravitational forces and internal dynamics of ice towards the sea. On reaching the ocean, a combination of various factors causes disintegration of the glacial ice into icebergs of different dimensions. The waters encircling the Antarctic continent are replete with icebergs and between Antarctic coast and Antarctic convergence these are driven westward by the Antarctic Coastal Currents (ACC), till they reach under the influence of Weddell Sea Gyre (Fig. 5.1). From here, the journey is reversed and the icebergs travel towards east.
Fig 5.1: Simplified Antarctic map showing surrounding ocean currents. (source: The Encyclopedia of Earth).
Ice shelf around the Antarctic coast is the mother of majority of icebergs (about 80%). It would be pertinent to mention here that an iceberg with 50 - 60m length and 10-15 m height above the water level may weigh up to 1 megaton and drifting of such a huge ice mass in the circumpolar Antarctic waters requires meticulous monitoring. Between one-quarter and one-seventh of an iceberg's mass appears above the sea surface. The rest is below the water and this is the part of the iceberg that is most dangerous to passing ships. Besides the navigational significance, the data on the frequency, size and shape of icebergs provides us significant insights into the long-term and short term changes in Southern Ocean environment.
5.2 Observation Programme During the Indian Expeditions to Antarctica, iceberg positions are monitored along the voyage route within a radius of 24 nautical miles using ship's Radar. The morphological features of the icebergs are recorded through binoculars when the ship is in the proximal position. The icebergs observation recorded is prepared as per the guidelines of the Norwegian Polar Institute (NPI). The first sighting of icebergs during successive Indian Antarctic Expeditions is an important feature of the iceberg monitoring
Fig. 5.2: Latitudinal positioning of first sighting of icebergs during subsequent expeditions.
programme (Table 5.1). The first iceberg was seen at 58°50'S latitude during the First Indian Antarctic Expedition (1982) whereas during 23rd Indian Antarctic Expedition (2003), the first iceberg was sighted as closer as 44°47'S latitude. The plot of first appearance of iceberg indicates a northward latitudinal shift (Fig. 5.2) over the years. Observations show drifting of icebergs in ENE direction between latitude 50° to 54°S.
5.3 Classification Based on Shape On the basis of the shape, icebergs are classified into tabular, pinnacled, serrated and weathered type. The tabular type (Fig. 5.3) is almost rectangular in shape, flat topped and shows characteristic horizontal layering. Such icebergs are generally observed in the proximity of ice shelf, are white in colour with rare development of caves and a characteristic lustre due to higher content of entrapped air (Kaul et al., 1985b, Ravindra et al., 1994a).
Fig. 5.3: Tabular Iceberg
All icebergs disintegrate over time as they float over the relatively warmer ocean water. The large icebergs can exist for many years. As a function of time spent in the ocean, the icebergs become progressively irregular in shape and show various stages of disintegration. Wedge (Fig.5.4), blocky (Fig.5.5), dome (Fig.5.6) and pinnacle (Fig.5.7). Shapes in these icebergs develop as a result of continuous action of waves and wind. Weathered icebergs show pronounced effect of erosional agents with serrated surfaces (Fig.5.8) and muddy yellow to greenish colour depending on the density of ice. Near the coast, some icebergs come in contact with sea floor with restricted movement and occasionally get trapped in the sea ice are called Grounded icebergs. Large icebergs at times tilt and overturn due to wave and wind action.
Fig. 5.4: Wedge shaped iceberg
Fig. 5.5: Blocky iceberg
Fig. 5.6: Dome shaped iceberg
Fig. 5.7: Pinnacle shaped iceberg
5.4 Classification Based on Size Icebergs are classified as per the visual estimates of their longest dimension into the following; Class I
II III IV
50m – 200m – 500m –
50m 200m 1000m
Fig. 5.8: Weathered iceberg
5.5 Distribution Pattern A case study done during 2004 showed that Class-I icebergs constituted about 25% of the total icebergs sighted and were generally localized in the northernmost zone. The Class-II icebergs were more frequent between latitudes 550 and 660 S and constituted about 35%. The Class-III type icebergs were noted between latitudes 550 and 600 S and constituted about 31% while Class-IV and V types of icebergs constituted about 8% and less than 1 percent, respectively. The Class-V icebergs (largest ones) are frequent in the vicinity of the Antarctic Shelf. It has been observed that the icebergs generally do not survive beyond latitudes lower than 440 S. Majority of icebergs are observed to be concentrated in two prominent zones separated by an iceberg free zone (Ravindra et al., 1994b; Mukerji et al., 1995; Gaur et al., 1996; Jayapaul et al., 2000, 2001) (Fig. 5.9). The red and green circles represent iceberg concentrations as recorded in 24th (2004) and 28th (2008) Expeditions, respectively (Table 5.2). These zones occur between latitude 49°and 69° S with variable positions in different years. The concentration of icebergs in these two zones and their overall distribution pattern can be attributed to the prevailing ocean currents in this area.
5.6 Implications on Climate In recent years the global surface air temperature (SAT) has shown a warming trend (Alley et al. 2003) along with a rise 0.5°C in ocean water temperature surrounding Antarctica (Jacka and Budd, 1998). The re-analysis of data (NCEP-NCAR: National Centre for Environmental Prediction-National Centre for Atmospheric Research) has also reflected similar increase in the linear SAT trends over 1979 2004 (Kalnay et al., 1996). Moreover, it has been observed that since 1950, the Southern Ocean is warming faster than other oceans in the world (Gille, 2002). The average global ocean temperature in the upper 1000 m has increased by 0.1°C between 1955 and 1995, whereas the mid depth Southern Ocean temperature has risen by 0.17°C (Levitus et al. 2000). Although satellite observations between 1982 and 1998 show cooling over parts of the Antarctic continent, a general warming occurred in the surface temperature of the peripheral seas (Kwok and Comiso, 2002, Zhang, 2007). The latitudinal shift in the position of first sighted iceberg towards the lower latitude along the voyage route of Indian Antarctic Expeditions may be related to the overall change of surface air temperature in this sector of Indian Ocean. Significant impact of climate change has been observed in the southern ocean adjacent to Antarctica since last few years. The role of Antarctic Circumpolar Current (ACC) that circulates around Antarctica is important in controlling the temperature of the Southern Ocean and the climate of Antarctica. As the ACC flows eastward through the southern portion of Atlantic, Indian and Pacific Oceans it transports more water than any other currents and thus have aprofound control on Antarctic climate (Pickard and Emery, 1990) encircling Antarctic continent (Klinck and Nowland, 2001). Its vast cross-sectional area of influence with large volume of water affects the distribution pattern of icebergs in this region. The eastward flow of the Sub-Antarctic Front (SAF) located between 48°S and 58°S in the Indian and Pacific Oceans defines the ACC's northern boundary whereas a region of upwelling called The 'Antarctic Divergence' was considered to be its southern boundary (Klinck and Nowlin, 1986). However, the southern boundary of ACC has shown further poleward shift upto 65°S in this part of southern ocean (Orsi et al. 1995). Iceberg drifts have been used to obtain information on the coastal current and its variation (Tchernia and Jeannin, 1980; Ohshima et al., 1996; Gladstone et al., 2001). Holocene records of sea-surface temperature (SST) and sea-ice duration (SID) from the Southern Ocean demonstrate strong regional / latitudinal heterogeneity (Bianchi and Gersonde, 2004; Nielsen et al., 2004; Crosta et al., 2007). Any change in SST and SID is well reflected in icebergs and their distribution pattern. The present analysis shows that the eastward shift of icebergs, as observed in the Indian Expedition voyage route, can be correlated to the Sub-Antarctic front (SAF) and Antarctic Circumpolar Current (ACC) and the northward shift in the concentration zones of icebergs as well as the distribution pattern in the past two decades were affected by the rising Surface air and ocean temperatures.
Table5.1 Positions of first and last sighted icebergs during different expeditions.
Year Exp editio n
Latitu dinal p ositio n o f Latitu din al po sit io n of last first sigh ted iceber g sighted iceb erg °S (retu rn °S (o nwar d jou rney) jo ur ney)
I II III IV V VI VII VI II IX X XI XII XIII XIV XV
1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995
58°50 ’ 59° 55° ----------------55°41 ’ 55°42 ’ 52°29 ’ 51°23 ’ 60°19 ’ 51°12 ’ 50°19 ’ 47°22 ’ 57°44 ’ 53°45 ’
57°32’ ------------------------------------56°15’ -------55°15’ 55°30’ 64°42’ --------47°30’ 53°24’ 56°56’ 53°16’
XVI XV II XVIII
1996 1997 1998
53°28 ’ ---------53°51.06’
XIX XX XXI
1999 2000 2001
44°47 ’ 49°11.7’
XXV XXV I XXVII XXVIII
2005 2006 2007 2008
-------50°52 ’ -------59°52.71’
ermafrost can be defined as a layer of soil, any other surficial deposit, or bedrock lying at variable depths where temperature below freezing has existed continually for a long time (Muller, 1947). The properties of permafrost zones depend on local climatic, morphological and hydrogeological conditions (Huge and French, 2007). The presence and thickness of snow-cover also affects the permafrost behavior.
Fig. 6.1 Different components of permafrost layers.
A permafrost comprises of various components (Fig. 6.1) such as Active layer, Permafrost table, Isothermal permafrost, frost-free soil etc. The red dotted-to-solid line depicts the average temperature profile with depth of soil in a permafrost region. The trumpet-shaped lines at the top show seasonal maximum and minimum temperatures in the "active layer", which commences at the depth where the maximum annual temperature intersects 0° C. The active layer is seasonally frozen. The middle zone is permanently frozen as "permafrost". And the bottom layer is where the geothermal temperature is above freezing. Note the importance of the vertical 0° C line: It denotes the bottom of the active layer in the seasonally variable temperature zone and the bottom limit of permafrost as the temperature increases with depth.
6.2 Classification Black (1954) has classified permafrost on the basis of water content into super-saturated, saturated and undersaturated types. Most of the studies on permafrost have been done on wet soils that represent saturated and super-saturated types. The under-saturated type has pore spaces and lack visible ice-content. Davies (1967) examined the permafrost in dry areas of northern Greenland and concluded that permafrost conditions in extremely dry areas are markedly different from areas carved with wet soils.
6.3 Methodology A large part of the Antarctic continent depict arid climate of a cold desert and falls in the zone of continuous permafrost. Formation of soil in such regions is poor and it generally confined to morainal areas. Schirmacher Range is a rocky-oasis surrounded by polar ice sheet and ice shelf. The ice sheet has retreated, leaving behind a thin and sporadic cover of soil on an undulating terrain. The present observations are based on the study carried out at a location about 50 m north of Maitri station over a morainal soil of about 1 m over the bedrock (Chaturvedi and Asthana, 1996b). The prevalent high velocity winds do not permit the formation of any snow cover in the study area. The absence of snow cover and non-proximity to any water body ensures that the soil is undersaturated. The altitude of the study site is about 110 m above the mean sea level. A small pit was made to reach the bedrock at one metre depth. Five calibrated thermistors (PT-100) were installed in the pit at a uniform depth interval of 20 cm from the surface. The thermistors have a range of -40° C to +20° C and an accuracy level of ±0.1° C. The pit was filled up with the scooped out material to replace the original medium. A sixth thermistor was calibrated to record the ground surface temperature. Since the diurnal variations do not affect the sensors at a depth of one metre (Chaturvedi and Asthana, 1996b), observations were taken everyday in the afternoon, except on days when the blizzards prevented visit to the site. Data has been statistically analysed adopting the models of Davis (1986), Rock (1988), Cooley and Lohnes, (1971). Following relationship has been applied to estimate the temperatures at depths using the surface temperature data of 10 consecutive days, T = [Y+(X0*T0)+ (X1*T1)+ (X2*T2)+ (X3*T3)+ (X4*T4)+ (X5*T5)+ (X6*T6)+ (X7*T7)+ (X8*T8)+ (X9*T9)+ (X10*T10)] where T is the temperature at depth; Y, X0 ….. X10 are constants, and T0…… T10 are temperatures at the surface for day-0 to day-10.
6.4 Observations A total span of 691 days spreading across two polar winters (11th March 1996 to 30th January 1998), is covered by the present study. The constraints due to Antarctic weather conditions permitted observations on 358 days (Table 6.1). On each observation day, thermal data from 6 thermistors were recorded. However, late in August 1997, the bottom-most thermistor (at 100 cm depth) developed some mechanical fault and its data could not be recorded afterwards. The day-to-day observations are presented in Table 6.2.
6.5 Outcome During the period under observation, the temperature rose to positive values for nearly one-third duration (31%). However, the observed and calculated temperature values for the entire depth of 1 m show that it had attained the freezing point. The average surface temperature over the observation period ranged between -29.3°C and +16.3°C but at 100 cm depth the range is limited between -16°C to +2°C. The mean minimum temperature (calculated) for two consecutive years shows a slight difference only in the shallow layers at 20 cm, whereas the mean maximum temperature (calculated) shows fluctuation in the top and bottom layers. The observed as well as calculated minimum temperature increases with depth gradually. The observed as well as calculated maximum temperature increases with depth gradually the same pattern in two successive years. It is seen that the difference in temperature of surface to the 20 cm depth is more drastic in comparison to that between successive layers at depth that might indicate more stable thermal properties. Interpretation based on bulk daily data, as depicted in Fig. 6.3 shows that at 20 cm depth, 29 percent days show positive Fig. 6.2: Comparison of minimum and temperatures, while at 80 cm depth, this is reduced to 10 maximum temperatures in two polar seasons. percent. At 100 cm depth, the percentage of such days is about 3 percent, although the data at this depth is only for one polar summer. Analysis of bulk data also shows that thawing of ice starts from middle of November to first week of December every year and it takes almost a month's time for complete thawing from 20 to 80 cm. It is observed that the dates on which summer thawing sets in varies considerably on and near the surface, but at depth, it takes place within a week. It is apparent from Fig. 6.2 that, the mean temperature decreases with depth (Fig. 6.2). However, the difference between mean temperatures at 60, 80 and 100 cm depths is very small. It is observed that the deviation from the mean temperature is less with respect to the increase in depth, ie the thermal properties become more stable with depth. Therefore, the immediate change (same day correlation) with respect to the surface is maximum at the first level and becomes less with depth. It is also seen that there is nearly a perfect correlation between 80cm and 100 cm levels with respect to immediate surface influence. So with increasing depth, the differences in effectivity of surface temperatures taper out. The amplitude of temp fluctuations (Table 6.2, Figure 6.3) also shows a gradual declining trend with the depth. The overall surface temperatures ranged from 29.3° C to +16.3° C, but at 100 cm depth the range was only from -16° C to +2° C. It is also interesting to compare the minimum and maximum values for two different polar summers and polar winters. The values are almost similar, confirming the thermal limits of these active layers. The temperatures remained below the freezing point most of the time. However, it rose above the freezing point at all the recorded depth levels, indicating that the entire observation zone of 1 m thickness is within the active layer of permafrost.
Data for thawing of ice in two successive years shows that; It starts from middle of November to first week of December It takes almost a month's time for complete thawing from 20 to 80 cm.
The cross-correlation series (Fig. 6.2) show that there is a distinct lag in the maximum effect of surface influences as depth increases. The 20 cm depth has a lag of 1 day, 40 cm depth has a lag of 2 days, 60 cm depth shows a lag of 3 days, while both 80 cm and 100 cm depth levels display a lag of 5 days. Regression coefficients have been calculated for different depths. It is observed that the calculated temperatures for 60 cm and 80 cm deep layers fairly match with the observed average temperature, while those for the uppermost layers of permafrost are similar in trends but not very reliable. Thus, it may be stated that a predictive relationship with the surface temperature can be formulated for deeper levels of permafrost, while the near-surface levels are influenced by surface fluctuations to permit accurate estimation.
Fig. 6.3: Percentage of days with positive temperature at different depths. Table 6.1 Number of days showing temp above freezing point & Minimum and maximum temperatures during two polar seasons Depth i n cm
Total Number of Observ atio n Days
Days wit h Positi ve tem p
Per cent age of Day s with +ve temp (+ve temp %) 31.28
Observed Mini mum Temp (°C)
O bser ved Maximum Tem p (° C)
mi ntemp 96-97 (°C)
m intemp 97-98 (°C)
maxtemp 96-97 (°C)
m ax t em p 97-98 (°C)
Thawin g 96-97
16.11.9 6 7.12.96
24.12.9 6 29.12.9 6
31.12.9 7 7.1.98
Ground Penetrating Radar: Applications on Antarctic Cryosphere
7.1 GPR Technology
raditionally, drilling, echo sounding and microwave radar measurements were employed to gain information on the character of englacial and subglacial structures (Paterson, 1994). The technological advancement in the field of remote sensing had been useful in providing information on the nature of ice shelf and its relationship with the continental ice sheet. Over the last three decades, radio-echo devices and radar systems are being utilized to study a variety of large scale glaciological measurements. These systems are bulky (up to 40 m in length) and operating them in the rugged terrain at the glacier terminus is difficult. Radar systems operated from aircraft have provided some subsurface data, but the strong reflection from the air/ground interface limits the amount of energy entering the subsurface and affects the depth of penetration. Though the upper part of the snow/ice surface could be traced from the satellite imageries, the delineation of actual grounding line required information on the subsurface features beneath the ice.
Fig. 7.1: Schematic representation of the components of GPR system.
Ground Penetrating Radar has emerged as an important geophysical tool for assessment of the state of ice shelf and identification of subsurface features beneath in the Polar Regions. The main appeal of this tool is its non-destructive nature, low cost and time effective operation. GPR produces an accurate picture of the subsurface in two and three dimensions. Ground Penetrating Radar (GPR) system comprises a Subsurface Interface Radar (SIR) with a recording device (laptop / notebook), GPS, Survey wheel, connecting cables and high frequency antennas with centre frequency varying from 3000 to 15 MHz. All these components draw power from a 12 V battery. The system sends electric signals and received by its antennae (Fig 7.1). In this process, different dielectric properties of different media have been identified using following equations, Er=[c/v]2
Where Er is dielectric constant, c is velocity of light and v is velocity of electromagnetic wave passing through the medium. D = (2.32t)/ √Er
Where D is depth of target in cm, t is wave travel time in nanosec, 2.32 is a constant incorporating speed of light and conversion units and Er is dielectric constant of the medium.
Fig. 7.2: A) -100 MHz antenna attached to the snow vehicle using 'D' shackle. B) Survey wheel attached to antenna assembly for ground control. C) Control unit and recording laptop arranged within the heated cabin of snow vehicle. D) 200 MHz antenna attached to the front bracket after removing the bucket.
As batteries drain out quickly in the extreme cold conditions of Antarctica, power was drawn directly from the vehicle battery using suitable fabrication done at the Maitri station. During the surveys carried out between 2008 and 2012, MLF antennas (35 MHz and 80 MHz centre frequency) along with 200 MHz frequency shielded antenna were used. A Y-shaped bar was fabricated and connected behind the vehicle using a D-shackle for dragging the antennas on the ice surface (Fig 7.2A). A calibrated survey wheel was attached to the structure for acquiring exact control over distance travelled by the antenna (Fig 7.2B). The SIR-20 control unit and the toughbook are kept inside the heated cabin of the vehicle, so that desired operating temperature is maintained (Fig 7.2C). The control unit and the antennas were connected by a 30 m long control cable. The Multiple Low Frequency (MLF) antenna is unshielded and has separate Transmitter and Receiver systems requiring additional power for transmission. A four meter long wooden platform was prepared for keeping the transmitter and receiver spacing at 1, 2 and 3 meters according to requirement. The spacing was dynamically changed during the surveys depending on the targeted depth and desired resolution. The frequency of the MLF antenna was modified by varying the length of the telescopic elements on either side of the main unit. All antennas were tested on snow surface near the station before commencement of the work. In order to make the system efficient, weather proof and effective, some modifications were done to mount the entire system on to different types of snow vehicles. During the 29th expedition (2009-10) an extendable steel arm of 3.5 m length was fabricated for mounting the 200 MHz antenna on the Pisten Bully-300 after removing the front bucket (Fig 7.2D). The system was run in continuous static mode generating a continuous subsurface profile along the traverse line. When running in continuous mode, the antennas were dragged at a constant speed and the profiles were pegged to ground surface using calibrated survey wheel as well as a handheld GPS unit. Common parameters used during the data collection are given below. Table : 7.1 Parameters used during the data collection Antennafrequency
Samples / scan
Scans / sec
12 - 20
The dielectric constant for polar ice was kept at 3.0. This value of dielectric constant was calculated during 28th ISEA by velocity analysis using the common midpoint survey. During the course of survey, the range (time for which the radar listens for reflected signals) was changed depending on the location of survey and target depths. About 100 linear km of profile data has been collected from 2008 to 2012. The acquired data was processed using the RADAN software (6.0 and 6.5 versions). GPR signals propagate extremely well through ice and produce long diffraction tails from point-source reflectors. The use of digital enhancement techniques was kept to a minimum while processing the GPR profiles since excessive use of such artificial enhancements tends to mask actual signals. Variable gain and a high/low pass frequency filters were applied to the data.
Fig. 7.3: Composite of about 20 km GPR profile northward from Baalsrudfjellet to shelf revealing the ice-bed rock interface from 0 m to about 380 m below surface.
7.2 Scope of The Work The Antarctic ice sheet is dynamic and continuously moving towards north under the influence of gravity. The portion of ice sheet, which floats over the sea, is called ice shelf. The loci of points along which the ice sheet starts floating over ocean is called grounding line or hinge line. The three media viz: Land-Ice-Sea (LIS) meet along the grounding line. The grounding line is not fixed but keeps shifting in response to changes in glacial dynamics as well as climate change. The location of grounding line is important in order to evaluate the dynamic processes affecting the surface mass balance of ice sheet. The present study carried out during the years 200811 has provided significant inputs to the mass balance of Antarctic ice and in estimating the vulnerability of the ice shelf to calving which affects the land cargo routes between Maitri Station and the docking area of the ship carrying the supplies for Indian and Russian Stations. Lake Untersee is a large subglacial freshwater lake in the northeastern parts of the Gruber Mountains of central Dronning Maud Land (cDML) in East Antarctica. It is about 100 km southwest of the Schirmacher Oasis. The lake is bound by the Anuchin glacier in the north and Grubber Mountain from all the rest three sides. It has gained significance due to its unique nature such as presence of highly alkaline water content, anoxic conditions and presence of methane gas in parts (Wand et al, 2006). Ground Penetrating Radar (GPR) survey was carried out in the austral summer of 2011-12 over Lake Untersee to decipher the depth profile of the lake.
7.3 Mass Budget Of Ice Shelf The density of Antarctic ice over continental sector is 0.65 gm/cc at the surface and becomes nearly constant at 0.93 gm/cc below 30 m (Chaturvedi et al, 1999a). For volume calculations, it is assumed that the ice thickness is uniform for the study area and that the average density of Antarctic ice is 0.85 gm/cc. GPR surveys from south to north (Schirmacher Range to coast) could reach to a point where the maximum ice thickness was observed to be 700 m whereas while proceeding from north to south (coast to Schirmacher Range) maximum thickness of ice was estimated at 125 m. For the left over length of about 38 km a uniform thickness of 500 m (based on the trend of ice thickness as recorded by GPR) is assumed. The volume of shelf ice in India Bay Region is calculated as 6900 cubic km. The volume of ice in the ice cap area is calculated to be 340 cubic km. Thus the total volume of ice for a stretch from Ballsrudfjellet Nunatak to the shelf edge is about 7240 cubic km. Assuming an 3 uniform density of 0.85 gm/cc for the ice, this volume of ice amounts to about 6154 km of water equivalent.
7.4 LAND-ICE-SEA (LIS) Interface The Antarctic ice sheet together with the ice shelf, plays an important role in influencing the global climate. Antarctic ice sheet is thickest in the central part and constantly flows outwards mainly under the influence of gravity. There is a continuous build up of ice in the interior of the Antarctic continent and simultaneous destruction at the periphery along the ice shelf. Differential GPS measurements on the velocity and principal strain rates of polar ice sheet south of Schirmacher Range show an average velocity of 6.21 + 0.01 cm per annum towards the north-northeast (Sunil et al., 2007, 2010). Ice shelf varies in size and shape depending on the mass balance of the ice-sheet in a particular region. It is cantilevered on one end at the triple junction of land-ice-sea while TFig. 7.4: Surface elevation profile of the line along which GPR data the other end floats over the sea. The was collected from Princess Astrid coast. loci of this triple junction (L-I-S interface) are referred to as the grounding line. The principal objective of the present work was to identify the grounding line east of the Schirmacher Oasis and to locate subsurface features such as sub-surface mounds that may act as pillars supporting the ice shelf. Quantification of the total ice mass (variation in thickness) in the India Bay region for long term monitoring was also attempted.
The contrast between the dielectric permittivity of ice, bedrock and ocean water provides the basis for use of GPR to delineate the interfaces below the ice cover. The northern margin of Schirmacher Oasis manifests a steep escarpment and forms the grounding line exposed on the surface. This contention is supported by the presence of pressure ridges on the ice surface to the north of the escarpment. These pressure ridges have formed due to tidal pressure that forces the ice mass towards the rigid boundary of the continent. Another indication of the grounding line along the northern margin is the existence of epi shelf lakes which are connected to the ocean as indicated by the rise in water level during high tide. Schirmacher Oasis tapers off below ice cover in the east and west but the exact location of the grounding line is unknown in both directions.
Fig. 7.5: The 12 km GPR profile with 35MHz antenna configuration showing ice-bedrock interface picked up at a depth of 360m below polar ice on the Polar ice-cap and continues upto 500 m depth
Making optimum use of the logistics available during the austral summers from 2008 to 2012, GPR profiles were collected in a north-south stretch (about 40 km east of Schirmacher) to constrain the L-I-S. During the course of work in 28th ISEA, it was observed that the ice thickness increases rapidly from 0 m near the northern edge of Baalsrudfjellet Nunatak (where rocky outcrops are exposed) to 380 m near the reference point A-12 (of convoy route) (Fig. 7.3). This location is about 20 km from the edge of Baalsrudfjellet Nunatak. The surface elevation profile (Fig. 7.4) shows that the topographic height also decreases rapidly from 457 m above mean sea level (MSL) to about 100 m above MSL at A-12. The vertical resolution of the 35 MHz antenna is 3 m and the radar generated profile is a cumulative of the subsurface layers (Moore, 1988). Absence of many prominent reflectors in this zone points towards the cold and stable ice condition. Larger (3 m) vertical resolution for the antenna (35 MHz centre frequency) as well as long trace of the wave prevents the antenna to pick up weaker reflectors (Sinisalo et al., 2003). The subsurface data obtained during 29th expedition shows that the ice thickness increases from 380 m near A-12 to about 500 m near G-30 (70° 44.979' S: 12° 29.121' E) that lies between convoy reference points B1 and B2 and is located about 12 km northeast of A-12 (Fig. 7.5) with variation in the ice thickness in between these.
Fig. 7.6: GPR profile obtained on India Bay shelf using 200MHz antenna. The observed Ice-Sea interface varies from 28 m near the seaward end of shelf to about 60m inward.
Fig. 7.7: GPR profile showing Land-Ice-Sea interface, (hinge line or grounding line).
GPR survey in the ice shelf area in India Bay Region using 200 MHz antenna has shown that the ice thickness increases rapidly from 28 m, near the coast, to 60 m about 2 km inland (southwards) (Fig. 7.6). Topographic profile suggests average height of 22 m above MSL in this area (Fig. 7.4). This shows that more than 40 m thickness of the ice remains submerged below sea level in this area and it rapidly increases southwards. The data collected during 31st expedition using 80 MHz antenna shows that the ice thickness ranges from 30 m near the shelf edge to 125 m at a location 30 km inland towards south. The corresponding surface elevation varies from 10 m to 41 m above MSL (Fig 7.4). A prominent reflection at 25 m observed throughout the profile possibly marks the transition from firn to ice. Other minor reflections represent isochronous ice layers (Sinisalo et al., 2003). Absence of many prominent reflectors in this zone points towards the stable ice conditions. A possible loci for L-I-S was detected at latitude 70°51.090'S and longitude 12°14.429'E that gets expressed as a steeply sloping land-ice interface juxtaposed against gently sloping sea-ice interface (Fig. 7.7). This juxtaposition is observed at 340 m below the ice sheet that was later confirmed in a closely spaced profile line generated during 30th expedition. Convex nature of the bedrock has been observed in one profile (Fig. 7.8) north of the grounding line during 29th expedition. This structure is about 500 m long and 30 m higher than the background in this part. However, this structure could not be termed as subsurface mound due to its smaller dimensions.
Fig. 7.8: Low convex mound in the bedrock below 300 m as revealed by GPR profile
7.5 Lake Untersee Lake Untersee (Fig. 7.9) is a large subglacial freshwater lake in the Gruber Mountains of central Dronning Maud Land (cDML), East Antarctica. It is situated approximately 100 km to the southwest of the Schirmacher Oasis. The lake is approximately 6.5 km long and 2.5 km wide and is surrounded by Gruber Mountains on east, south and west. It is bound by the Anuchin glacier in the north, which topographically dips towards the lake. The lake is divided in to two sub-basins by a morainal ridge (Wand et al, 1997). It has gained significance due to the presence of highly alkaline water, methane gas in parts and anoxic conditions (Wand et al, 2006). Recent investigations by the TAWANI group of scientist were successful in locating rich benthic biota in the lake bottom (Andersen et al, 2011). The Untersee Lake has presumably formed during the last glacial minima and is perennially covered by ice under subglacial environmental conditions.
Ground Penetrating Radar (GPR) survey (Fig. 7.10) was carried out in the austral summer of 2011-12 during 31st Indian Scientific Expedition to Antarctica (ISEA) over Lake Untersee, to decipher the depth profile of the lake and its surroundings. The vertical as well as lateral variations in the frozen surface of the lake are delineated using the GPR profiles. The data was collected using SIR 20 GPR system with 400MHz antenna in a free run mode. The frozen upper surface of the lake shows high degree of lateral and vertical variations mainly reflecting variable compaction of different ice layers. The surface ice layer over Lake Untersee is found to vary from 1.5m to 4.5m. At least two to three interfaces can be deciphered within a depth of 35m of GPR profile which probably result due to vertical stratification in the lake owing to contrasting physical and chemical properties. The longitudinal (Fig. 7.11) and transverse (Fig. 7.12) GPR surveys over the Lake Untersee show that this huge lake has two sub-basins separated by a NW-SE trending ridge at a depth of 45-50 m below the lake surface. The northern sub-basin of the lake is very deep and thus the water column bedrock interface could not be picked up upto a depth of 150-190 m. The deepest part of the southern sub-basin could be probed upto 100m, below which clay is present. The peripheral part of the southern sub-basin shows the presence of bedrock at a depth of 5-27m. The bedrock shows undulating topography. The perennial ice cover of the lake has a variable thickness ranging from 2.5m in the southwestern part to 4m in the eastern part. The Anuchin glacier damming this lake towards north shows its extension into the lake below the visible surface. Several visible cracks on the lake surface have probably formed due to continuous movement of the glacier towards the lake and have also given rise to a series of Push ridges near the contact.
Fig. 7.9: Map showing Lake Untersee with GPR traverse lines. Red markers show sounding depths of the lake as measured by TAWANI scientists.
Fig. 7.10: GPR survey in Lake Untersee, East Antarctica.
Fig. 7.11: Longitudinal GPR profile up to 30m of Lake Untersee from north to south using 400 MHz antenna.
Fig. 7.12: GPR profile across the Lake Untersee up to 30m of Lake Untersee from west to east using 400 MHz antenna.
SI has collaborated with National Centre for Antarctic and Ocean Research (NCAOR) Goa to decipher the palaeoclimatic history by analyzing the ice cores raised from Central Dronning Maud Land area of East Antarctica. In the same line GSI has collaborated with Indian Institute of Geomagnetism (IIG) to study the movement patterns, stress and velocity of ice sheet, south of Schirmacher Range with the help of Global Positioning System (GPS).
8.1 Ice core studies Antarctic ice core studies have provided useful information on past climatic changes. Drilling of ice core in Antarctica was initiated by GSI in 1992-94 with the help of hand held auger drill. Since then, seven shallow boreholes have been drilled (Fig. 8.1) in Antarctic Ice within an area of about 200 km2 in different locations of coastal ice shelf and continental ice sheet. The total length of ice cores recovered is 477m. The glacio-chemical and stable isotope data of shallow ice cores from the coastal Dronning Maud Land, East Antarctica is used in the present study for reconstructing the coastal Antarctic environmental variability during the past.
Fig. 8.1: Different locations of drilled ice cores in East Antarctica.
Ice sheets represent the most high-resolution (seasonal/ annual/ decadal/ centennial) and truthful time machines. The data generated from these studies can provide useful insights into the response of East Antarctic environment to the changes in global temperature, circulation and extreme events including volcanic eruptions during the past few centuries. Ice gets accumulated over a period of time and preserves the history of atmospheric temperature and records of atmospheric gases, wind-blown dust, ash, or even radioactive particles. Shallow ice core drilling, in East Antarctica was started for understanding the nature and variability of the soluble, insoluble, and isotopic components of the material induced by atmosphere and the ocean in annual to decadal scale. The proxies used for the interpretations are as follows:
1. Tephra / Micro-tephra- Proxies for volcanism and as a dating tool 2. Trace elements- Proxies for environmental change 3. Stable isotopes of O & H - Proxies for air temperature & humidity 4. Pollens & Diatoms- Proxies for environment and wind transport 5. Major ions (SO3, NO3, F, Ca,) Proxies for dust and volcanism The generated cores were physically logged in the field and the recovered length was properly packed, labeled in clean LDPE rolls and safely stored in Expanded Poly Propylene (EPP) boxes and transported to the subzero reefer containers (-20˚C) to Cold Lab of NCAOR, Goa for further processing. Samples for chemical analysis were prepared after allowing sampled ice cores to melt down at room temperature. Major ionic concentrations were analysed by Ion Chromatography, trace elements by ICPMS and oxygen isotopes by SIRMS.
8.2 Thermal and Density Profiling of glacier in vertical section Thermal profiling for the boreholes was done during 15th IAE (1995-96), It was observed that the variations in the polar cold front penetrated up to a maximum depth of 25m. Beyond this depth, the temperatures remained uniform throughout the year (Chaturvedi et al., 2001). The highest temperatures were recorded at the bottom (75m) of the glacier. Ice core from the first drill hole (IND-2) that touched the bed was subsequently utilized for recording thermal profiling of the glacier (Fig. 8.2). The overall average thermal variations in this borehole from surface to bedrock were confined to a small thermal band of -7.50C to -11.50C with lowest average temperature at 4m depth. The zone of temperature-inversion was observed between 25m and 30m depth. Beyond this zone, the temperature gradually kept on rising till the borehole reached the bedrock.
Detailed density profiling and extensive core photography was carried out in the field. The ice core from the bore hole shows almost a uniform density of 0.88-0.90 g/cm3, as upper fern is absent In the second borehole, the density of topmost layers of firn is around 0.4g/cm3. The first appearance of the blue ice shows a density of 0.86g/cm3. At the deeper level blue ice has an average density value of 0.91 g/cm3. So the overall variation of density in the column ranges between 0.4 g/cm3 to 0.9 g/cm3 (Nijampurkar et al., 1985) (Fig. 8.3). The mean annual rate of accumulation calculated to ~19 cm per annum in the last 200 years.
Fig. 8.2: Thermal profile of ice sheet in East Antarctica, south of Schirmacher Oasis showing point of thermal inversion.
The proxy indicators of palaeoclimatic record are preserved as atmospheric air, gases, pollen, dust, volcanic emissions and pollutants in the Antarctic ice sheet. The 18O content of ice shows a general linear relationship with prevalent surface air temperature, making it possible to establish a palaeotemperature-isotope relationship. The spontaneous explosion of the ice core obtained from the bottom of this borehole could be due to compression under severe strain at the depth, which disintegrated after surfacing. Alternatively, this could be a case of comparatively “warm” ice core from the depth receiving a colder thermal shock on the surface, which caused its disintegration.
Figure 8.3: Density profiling of ice core drilled during 15th IAE
8.3 Marker horizons for volcanic and extra-terrestrial activities in ice cores The depth profiles of electrical conductance, 18O, 210Pb and cosmogenic radio isotopes 10Be and 36Cl have been measured in a 30m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using 210Pb and18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ~150 years. Using these accumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical conductance measurements. The fallout of cosmogenic radio isotope 10Be compares reasonably well with those obtained from other stations (73°S to 90°S) in Antarctica and higher 36 latitudes beyond 77°N. The fallout of Cl calculated during the present work agrees well with the mean global 210 production rate estimated earlier by Lal and Peters (1967). The mean accumulation rate of ice based on Pb 18 (20 + 2 cm/yr), O (21 + 0.02 cm/yr) and conductance (17 + 0.05cm/yr) has been estimated to be ~19cm/yr in polar ice near the Indian station in East Antarctica for the past 150 years. A major marker horizon of mega-volcanic signatures of 1815 AD was identified ('Tambora' in Indonesia at 10°S latitude) at a depth of 30 m from the 60.46 m ice core that was raised from the continental ice sheet (70°47'S, 11°44'E) in central Dronning Maud Land, East Antarctica during winter period of 1993. Another sharp peak of a volcanic eruption of 1963 ('Augung' at 10° S latitude) was identified at 5 m depth in this ice core. These marker horizons consist of acids and micro particles. The mean accumulation rate deducted from the marker horizon of 'Tambora' is ~17 cm per annum. Isotope studies of 36Cl indicate that the cosmogenic fall-out in Greenland in the Arctic is higher by a factor of ~6 compared to the present site in Antarctica. The accumulation rate, however, shows significant interannual and decadal variations. The mean annual surface air temperature (MASAT) data observed during the last 150 years showed that the beginning of the 19th century was cooler by about 20C than the recent past and middle of 18th century. It is intriguing that, unlike in Greenland, 36Cl bomb pulse during the nuclear testing period (1940-1980 AD) is missing in the present 36 10 location of the ice core in East Antarctica. The mean Be/ Cl ratio of 7 for the last ~40 years may be used as the initial value to date older ice from east Antarctica (Nijampurkar et al., 2002).
8.4 Origin and characterisation of microparticles Polar ice cores are important natural archives of paleoclimatic changes, as they indicate large variations in atmospheric dust load in association with the past climatic changes. This deposition acts as fingerprints of significant geological events such as glacial weathering, volcanic eruptions, cyclones and tsunamis (Petit et al. 1999; Laluraj et al. 2006). Some of these dust particles are exclusively of aeolian origin, carried by wind that blows long distance across the continents. Large volcanic eruptions may also be detected in polar ice cores by the associated ash and cryptotephra particles (de Angelis et al. 1985; Palais et al. 1990; Silva and Zielinski 1998; Zielinski et al. 1997; Davis et al. 2004). Volcanic emissions lead to fallout of both gaseous aerosols and solid (tephra) components, which can travel great distances.
A 62.20 m long core (IND-22/B4) was collected from the continental ice sheet during the 22nd Indian Antarctic Expedition (Table). The selected samples from 0.50, 2.50, 9.40, 19.50 and 41.70 m revealed signatures of major volcanic events during 1991, 1963, 1883, 1815 and 1600 A.D (Thamban et al., 2006). Among these, two intervals of recent and well known volcanic eruptions of Augung (1963) and Krakatau (1883) were studied in detail to decipher the microbial cells attached to volcanic particles. The microparticles which included siliceous, carbonaceous and certain biological forms were observed attached or dropped on the surface of siliceous particles. The SEM observations indicate that the smooth particles resembled glass shards with sharp features, whereas the rough particles have undergone weathering during their transport. This variability could an intrinsic feature derived from their provenance or reworking during transport. The chemical composition and morphology shows that the smooth-surfaced particles are homogeneous as compared to the rough-surfaced particles and their formation may be attributed to fragmentation of quenched magma as a result of quick chilling during hydration (Heiken, 1972). The particles containing high silica and resembling glass shards could be the primary fallout of volcanic eruptions (Bjorck et al., 1991; Narcisi et al., 2005; Pattan et al., 2002), whereas the particles having rough surface indicate signatures of weathering and transport from the continental dust. This is further substantiated by a ternary plot of smooth and rough particles with CaO, FeO and K2O as end members showing a distinct difference in composition, thereby suggesting its difference in provenance through volcanic and continental dust. The volcanic particles (tephra) at the site are stratospherically transported, whereas the crustal dust particles could be wind transported and could have been from a local source in the ice-free areas of Schirmacher Range and the Tallaksenvarden nunatak. The EDS analysis showing particles rich in carbon are represented as carbonaceous particles. These particles are further classified into two groups; one enriched in both carbon and calcium and the other containing 100% carbon (purely organic). These bodies do not represent any individual microbes, but might have been derived from organic detritus or pieces of larger multicellular organisms. Some of the strange forms resembling cotton balls or coiled coir do not represent a new organism, instead their age and habit might have resulted in their unusual shapes.
8.5 Inferences on Antarctic climate change using Ice Core Proxy Records Temporal records of ionic concentrations and stable isotope ratios in the ice cores from coastal Antarctica provide excellent proxies of recent Antarctic climatic variability and the factors influencing the changes. The ice core raised during 22nd Expedition was used in this study. Sea salt ion data indicates a significant additional contribution of chloride ions compared to sea water values, possibly through atmospheric scavenging. The nitrate (NO3) profile exhibits significant temporal shifts than that of the sulphate (SO4) with a major shift around 1750 AD. The changes in NO3 record are synchronous with the proxy record of solar activity (10Be profile from a South Pole ice core), suggesting enhanced NO3 values during periods of reduced solar activity like the Dalton Minimum (~1790-1830 AD) and Maunder Minimum (~1640-1710 AD). The δ18O records reveal that the more negative δ18O values were coeval with several events of increased NO3 concentrations, suggesting enhanced preservation of NO3 during periods of reduced air temperatures. The δ18O and δD records of the core also suggest significant short-term and long-tem variability with more negative values indicating relatively lower air temperatures prior to 1715 AD. The δ18O records also revealed a significant warming of 2.7°C for the past 470 years, with a warming of ~0.6°C per century.
8.6 Inferences on Climate change from Nitrate records of shallow Ice Cores 18
High-resolution records of nitrate (NO3−), oxygen isotope (δ O) and non-sea salt sulphate (nssSO4−) were studied using an ice core collected from central Dronning Maud Land in East Antarctica to identify the influence of environmental variability on accumulation of NO3− over the past 450 years. The results confirmed that multiple processes were responsible for the production and preservation of NO3− in Antarctic ice. Correlation between No3− and nssSO4− peaks revealed that sulphate aerosols released during major volcanic eruptions might have activated the production of nitric acid, which was scavenged by ion-induced nucleation in polar ice sheets. The correlation between the nitrate and δ18O records further suggest that enhanced NO3− preservation in the ice occurred during periods of lower atmospheric temperature. Major shifts in the NO3− record of the ice core presently studied and its comparison with 10Be record from a core collected from South Pole suggest that a reduction in solar activity influenced the NO3− accumulation in Antarctica through enhanced production of odd nitrogen species. Nitrate records along with sulphate and oxygen isotope records in the ice core revealed that the temporal variability in nitrate records in Antarctic ice core are influenced by complex processes of production, accumulation and preservation of atmospheric odd nitrogen species. It is proposed that the scavenging of nitric acid in atmosphere by the non sea-salt sulphate forming multi-ion complex could be a mechanism influencing the deposition of nitrate in Antarctic snow. The relatively cooler periods (more negative δ18O values in ice core) were characterized by high nitrate deposition in the ice core, suggesting a temperature control in the accumulation of nitrate in snow/ice. The prominent variations in NO3− profile before and after ad 1750 correlate well with the 10Be records from Antarctica, suggesting the influence of solar activity on the No3− accumulation in snow (Laluraj et al 2011).
8.7 Inferences on climatic teleconnections from temporal isotopic variability Significant relationship between δD and δ18O in ice cores and the temperature at the precipitation site is observed at mid and high latitudes. Though the association of δ18O -T seems to be linear (Dansgaard et al., 1973), there are numerous factors such as temperature of source from which the moisture evaporated, subsequent cycles of condensation and evaporation, change in moisture source region, seasonality of precipitation etc., that make the interpretation of temperature from water isotopes difficult (Jouzel et al., 1997; Reijmer and Van den Broeke, 2001; Helsen et al., 2005). Most of these factors could be resolved using a second order isotopic parameter called deuterium excess (d = δD - 8 *δ18O) which depends on the temperature and relative humidity of the evaporative source which, in turn contains information about conditions prevailing in these source regions (Ciais et al., 1995; Jouzel et al., 2003). However, there are large-scale atmospheric circulations that influence diverse sectors in Antarctica to different extents (Turner, 2004). On an interannual to decadal timescale, tropospheric Antarctic circulation is known to be driven primarily by the El Niño Southern Oscillation (ENSO) and Antarctic Oscillation or Southern Annular mode (AAO/SAM) (Thompson and Wallace, 2000; Bertler et al., 2006). The AAO provides a means of coupling the Antarctic climate with that of lower latitudes, and changes in ENSO undoubtedly affect the AAO, but in a highly non-linear way (Turner, 2004). Combined, the two forcings have the potential to partially off-set or enhance their influence on each other and the Southern Hemisphere as a whole (Bertler et al., 2006). This study shows the extent to which the temporal isotopic variability represents prevailing temperatures and to evaluate the influences of large-scale climatic cycles such as ENSO, AAO and IOD existing in this region of central Dronning Maud Land.
During the 25th Indian Antarctic Expedition (2005-06), a 65 m long ice core (IND-25/B5) (Table) was recovered from the continental ice sheet. The El NiñoSouthern Oscillation (ENSO) is one such phenomenon which leads a pattern of warm and cold sea surface temperature (SST) anomalies in the central and eastern equatorial Pacific with coupled atmospheric changes. The ENSO is known to have a signature that extends to the mid and high latitudes in the Southern Hemisphere in the winter and summer. The ENSO effect on a seasonal and interannual timescale is monitored by the Southern Oscillation Index (SOI), which is the normalized pressure difference between Tahiti (17.5oS, 149.6oW) and Darwin (12.4oS, 130.9oE). Using the time series data and numerical analyses, several studies have shown that statistically significant teleconnection exist between atmospheric conditions in the tropical Pacific and those at extra-tropical latitude areas of the Southern 18 Hemisphere (Kwok and Comiso, 2002a & b). The δ O profile from the ice core shows resemblance to the Southern Oscillation index (SOI) for the period from 1986 to 2006. This relation seems to be negative, with 18 negative SOI values corresponding to higher δ O values and vice versa. The closest resemblance is found at the anomalous 1997-1998 negative peak in SOI which is also seen in the δ18O profile with values reaching as high as -20‰. The year 1997-1998 is known for the strong El Niño event which commenced in December. Negative SOI trends indicate warm ENSO events whereas positive trends indicate cool ENSO events or La Niña events 18 (Turner, 2004). High δ O values correspond to highly negative SOI peaks. Therefore there seems to be a possible positive correlation between the δ18O values in the analysed icecore and warm events during ENSO. Annual correlations show no significance for the period of 1986-2006. The seasonal cycle is important when considering the effects of ENSO. Seasonal correlations were made for austral spring [September-November (SON)], austral summer [December-January (DJF)], austral fall [March-May (MAM)], and austral winter [JuneAugust (JJA)]. The SON and DJF are the peak seasons for ENSO. A statistically significant (95% level) correlation was found between surface air temperature at the core site and Nino 4 during austral summer with 'r' value better than 0.4 at the 95% level. The correlation is noticed only during the summer period. There could be some other factors which lead to this behavior and need to be determined. A positive AAO/SAM index indicates a lower pressure over Antarctica. Kwok and Comiso (2002a) demonstrated that during times of high AAO index, most of east Antarctica experiences a cooling while the Antarctic Peninsula experiences a warming. At times when the AAO index is said to be in its positive phase, the westerlies are at their strongest. Over the last 50 years it has shifted to its positive phase during the summer and autumn, intensifying the westerlies over the Southern Ocean, warming the Antarctic Peninsula and cooling East Antarctica by a small amount (Thompson and Solomon, 2002). Van den Broeke and Van Lipzig (2004) argued that the winter cooling over east Antarctica during high AAO index is caused by a greater thermal isolation of Antarctica due to decreased meridional flow and intensified temperature inversion on the ice sheet due to weaker near-surface winds. During austral summer (DJF), we find that both SOI and AAO are anticorrelated with respect to surface air temperature of the study site. This observation that the ENSO warm events influence the surface air temperature only in summer at the study site may be due to the combined forcing of ENSO and AAO. The connections between the ENSO and AAO appear only in the season when the ENSO phases reach their mature stage and forcing is particularly strong, namely, the austral summer (Fogt and Bromwich, 2006). During this period, the negative phases of the AAO are dominant (Carvalho et al., 2005). It was also shown that AAO's influence is strongest during spring and winter (Van den Broeke & Van Lipzig, 2004). Over the last two decades, a trend towards more negative SOI and positive AAO has been observed, but summer SOI and AAO indices are slightly positively correlated since
1979 (Bertler et al., 2006). L'Heureux and Thompson (2006) found a significant correlation between ENSO and the AAO from 1979 to 2004 during austral summer. Such significant relation during 1980's and 1990's has also been observed by Fogt and Bromwich,(2006). To assess the combined influence of SOI and AAO on the central DML summers, we added to the summer SOI, the summer AAO and compared their combined index (SOIDJF+AAODJF) with the summer (January) 18 temperature at 'Novo' station, and with the δ O record over the common time period of 1986 to 2006 (Fig.5). The correlation between SOIDJF+AAODJF and Novo January temperatures results in a negative relationship (r = 0.34) and that of the January temperatures with annual mean δ18O with a weak positive correlation of r = 0.22. This relation implies that the annual oxygen isotopic content is influenced by the summer temperatures at our coring site which in turn responds to the joint forcing of SOI and AAO during austral summers. The in-phase relationship between the SOI and AAO modes during DJF probably amplifies the height and pressure anomalies in our study region and produces the teleconnections seen in the correlation analysis. White and Peterson, (1996) suggested that the ocean circulation could play a role in the transmission of ENSO signals to high southern latitudes via the Antarctic Circumpolar Wave (ACW). They suggested that the ACW in SST originated in the western subtropical South Pacific, and then spread south and east into the Southern Ocean, where subsequent eastward propagation took place via the Antarctic Circumpolar Current (ACC). However, the instantaneous correlation found in recent studies (Martinson and Iannuzzi, 2003) suggest that the propagation proceeds much faster, implying an atmospheric mechanism. During the high-index polarities of the AAO, an anomalous strong cyclonic circulation in the southeast Pacific leads to an anomalous equatorward (poleward) mean heat flux at the surface in the Ross/Amundsen Sea (the Bellingshausen/Weddell Sea), which encourages (limits) sea ice growth (Liu et al, 2006). The present study thus suggest that jointly the SOI and AAO influence summer temperatures in the CDML region which leads to the observed variations in oxygen isotopic content of the snow. In terms of AAO influence on climate in our study area, it is observed that negative (positive) AAO peaks are associated with warming (cooling). During conditions of AAO positive polarity (strong large scale westerly circulation), an eastward shift occurs in the position of the south Atlantic storm centre (Genthon and Cosme, 2003). This cuts off the atmospheric branch of the Weddell Gyre, causing surface temperatures in the Weddell Sea and over the Antarctic Peninsula to rise by up to 8°C. Compared to this a cooling of up to 5°C occurs locally in East Antarctica in places where near-surface easterly winds have decreased over the perennial ice. Most intriguingly, accumulation rate and temperature both are correlated up to the 1997 period after which both are anticorrelated. Such contradictory changes have been noted for the western DML and have credited to seasonality in precipitation, changing trajectories of cyclones and changing moisture sources (Isaksson et al., 1996). At places, the d-excess also shows large peaks which correspond to some of the major ENSO events during the last two decades. These maybe caused due to the cyclonic activity which are known to increase during the ENSO events. Wind speed is known to influence the d-excess though not in a linear way (Ciais et al., 1995). The influences of cyclones could create a substantial influence on the air parcel paths in this region. Again, high accumulation in the CDML seems to be associated with strong El Niño events. The annual accumulation record at our site shows that high accumulation occurred during the strong El Niño's of 1987, 1993 and 1997-98. The δ18O record from the ice core from the central Dronning Maud Land region, used in the present study and covering a period of past two decades does not show a significant relation to the annual temperature record, which seems to be related to the cyclonic activities occurring in this region. Interestingly, the temperature in this region is seen to be under the influence of joint forcings of ENSO and AAO during the austral summer which
in turn influences the annual δ18O variations. Furthermore, the ENSO and AAO forcing are found to be strongest during the summer period at the study region. The exact mechanism controlling the coupling between the two modes needs further study, and many questions remain unanswered. We also observe that the signatures of the IOD are not apparent in the air temperature and the annual δ18O variations at the study region. Snow accumulation for the last two decades illustrates a significant decreasing trend that could be related to a change in cyclonic trajectories and also demonstrates a varied relation with the summer temperatures. The correlation between temperature and accumulation before 1997 and anticorrelation more recently is attributable to changing source regions. Deuterium excess for this core suggests that prior to 1997 the moisture was derived from the colder polar waters. Also, d-excess values reveal the substantial influence of cyclones on the air parcel paths in this region. During the El Niño events there is an associated strong upper level advection which brings in moisture and heat from the mid-latitudes into the CDML region causing larger accumulation and atmospheric conditions warmer then the local mean which predominantly influence the summer temperature and hence the δ18O record. We suggest that it is difficult to envisage the regional climatic signals using single records in this area influenced by large cyclonic disturbances. Consequently, to obtain a reasonably detailed climatic account it is necessary to average several cores, possibly in close proximity to one another. This analysis serves to illustrate the importance of the circulation changes in determining the spatial pattern of oxygen isotopes and surface temperature anomalies (Naik et al., 2010a).
Fig. 8.4: The δ18O profile from ice core shows some resemblance to the Southern Oscillation index (SOI) for the period from 1986 to 2006
8.8 Climate variability in cDML based on stable isotope records Stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core, in order to reconstruct the coastal Antarctic climate variability during the last century and its relation to the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). The δ18O records showed a significant relation to the SAM (Fig. 8.4) with dominant 4 years variability, except during specific periods (19181927, 19381947, and 19892005) when ENSO teleconnection was established through the in‐phase relation between SAM and Southern Oscillation Index (SOI). An ice core, IND 25/B5 (Table) was used to understand the influence of two major modes of climate variability, Southern Annular mode (SAM) and El Niño Southern Oscillation (ENSO) on the isotopic variability as well as the
relationship between oxygen isotopes and surface air temperatures in this region. The δ18O record of the ice core, covering a period from 1905 to 2005, revealed a relation to SAM, which varied in time as observed in the annual as well as seasonal correlations between the two. An intermittent influence of ENSO was observed from the relationship between annual and seasonal Southern Oscillation Index (SOI) index on the δ18O record at specific intervals (19181927, 19381947 and 19892005). It was further observed that during these specified intervals, the SAM and the SOI indices were in‐phase, which indicates that the teleconnection of ENSO to the central DML occurs through the combined influence of SAM and ENSO (Naik et al., 2010b). A significant negative relationship between SAM and the ice core δ18O record was observed only when the ENSO years occurring within the above mentioned intervals (19181927, 19381947 and 19892005) were eliminated. This negative relationship between SAM and the ice core δ18O indicates that the negative polarity of SAM leads to less negative δ18O and warmer temperatures in the central DML, similar to the records from the East Antarctic region. On a decadal scale the SAM was seen to override the influence of ENSO on the δ18O record. As revealed by the NCEP reanalysis of the data for the period 19892005, the SAM and SOI indices show a significant negative relationship with surface air temperatures, during the austral summer. This relationship between SOI and surface air temperature suggests that during an El Niño year within the period of 19892005, warmer air temperatures prevailed over the central Dronning Maud Land (cDML). These evidences further support the finding that both the SAM and ENSO cause a combined influence on surface temperatures during austral summer in the central Dronning Maud Land. The deuterium excess record of the ice core showed a significant relation to the relative humidity record from adjacent Novolazervaskaya station. The presence of major shifts in deuterium excess record for the years when the ENSO influenced the d18O record was observed. This may indicate shifts in moisture source regions during the periods of stronger ENSO teleconnections. A significant warming trend of 1°C for the entire century was seen in the Surface Air Temperature (SAT), which was estimated from the d18O record. This is also corroborated by the instrumental data from the 'Novo' station as well as earlier ice core records (Naik et al 2010b).
Fig. 8.5: Fluctuations in δ18O value. The sudden increase in δ18O value over the minimum indicates a warning and delaciation phase
8.9 Inferences from Oxygen Isotope data from Ice Shelf 18
Analysis of oxygen isotope data shows sudden increase in δ O value over the minimum at different levels, which indicates a warming and deglaciation phase. At least four such events have been observed in the first ice core at 5, 17, 34 and 47 m depth, respectively (Fig. 8.5). These fluctuations in oxygen isotope data show climatic fluctuations through the length of the ice core. The physical observations of this ice core show the presence of layers of blue ice and snow indicating seasonal melting induced by temperature fluctuations in that area.
8.10 Ice sheet dynamics around Schirmacher Oasis Schirmacher Oasis in central Dronning Maud Land is a part of Antarctic rift system that has evolved in different stages since the Gondwana break up in Jurassic time (Lawver et al., 1992). The study area is divided into three distinct topographic units. These are the southern continental ice sheet, elevated nunataks and ice shelf in the north of Schirmacher Range. This region is characterized by gentle to steep gradient surface slopes with few sub-glacial highs and lows above mean sea level (Damm and Eisenburger, 2005; Meyer et al. 2005) along with criss-cross fractures and crevasses. Prior to 1970, ice flow velocity were measured using astronomical positioning techniques and stake readings. Now a days several space borne geodetic techniques including Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), Ice Cloud and Land satellite (ICESat) etc are available to monitor the glaciers. During 22nd (2002-03) and 24th (2004-05) Indian Antarctic Expeditions, study was carried out to understand the movement of glacier surrounding the Schirmacher Range in collaboration with Indian Institute of Geomagnetism (IIG), Mumbai. The GPS network in the south of Schirmacher Range with 21 sites (Fig. 8.6) having 5 km interspace networking was established to measure the horizontal movement of ice sheet. The base station (MAIT) was set up on exposed bedrock on Schirmacher Oasis. The GPS receivers in the field were powered by specially sealed 12V, 72 Ah charged batteries enclosed in non conducting boxes. All the sites were observed continuously for 48-72 hours duration with 30 s sampling interval and 15° elevation mask. The recorded GPS data organized into 24hrs segments, covered a Universal Time Coordinated (UTC) day and were analysed in three steps. In the first step the GPS carrier phase data were processed with the precise ephemeris from the International GPS Service (IGS) stations to produce Fig. 8.6: Different locations of GPS stations, south of Schirmacher position estimates. In the next step Oasis with the directions of glacier's movement (after Sunil et al., 2007). these data have been standardize with the help of daily solutions for station positions using GPS analysis Massachusetts Institute of Technology (GAMIT) and software (King and Bock, 2002). In the third step station position and velocity vectors at each site were obtained.
For a complete description of the flow field of a glacier, both the horizontal and vertical components of the velocity are required. However, this study was confined to calculate the horizontal velocity components only by imposing tight constraints (1 cm/a) on the horizontal components of the base station. Horizontal velocities of the glacier sites lie between 1.89±0.01 and 10.88±0.01 m a-1 to the north-northeast, with an average velocity of 6.21±0.01 m a-1. The principal strain rates provide a quantitative measurement of extension rates, -3 -1 which range from (0.11±0.01) × 10-3 to (1.48±0.85) × 10 a , and shortening rates, which range from (0.04±0.02) × 10-3 to (0.96±0.16) × 10-3 a-1. The velocity and strain-rate distributions across the GPS network in the ice sheet, south of Schirmacher Oasis are spatially correlated with topography, subsurface undulations, fracture zones/crevasses and the partial blockage of the flow by nunataks and the Schirmacher Oasis (Sunil et al. 2007). In a related study, the movement of ice sheet was also observed on year long basis through one polar winter. The vector movement of the glacier helps in bulging forward in the snout area of Dakshin Gangotri glacier. These extra bulged parts of the snout break down and melt away from the main glacial body during the polar summer resulting in a net retreat of the glacier (Chaturvedi et al. 1999c, 2003 and 2004).
Implications on Climate Change
laciological studies conducted in the area around Schirmacher Oasis during the last three decades were helpful in deriving some meaningful patterns and charting a cause for future work. Some of the significant observations in this context include continuous recession of snout of the Dakshin Gangotri Glacier and temporal variations in the accumulation parameters of snow on ice shelf. Bimodal distribution pattern of icebergs, relationship of the surface air temperature with active layers of permafrost and movement of polar ice sheet in the NNE direction are few other interpretations explained through the present compilation. The annual recessional pattern of Dakshin Gangotri Glacier snout indicates that major recession follows a peak 2 in every five years. Since 1996, nearly 4800 m area has been vacated by the shrinking snout of this glacier. This 3 3 recession has led to the disappearance of about 672 X 103 m ice, which is equivalent to 576 X 103 m of water. The average annual recession of Dakshin Gangotri Glacier does not show any linear correlation with average annual surface air temperature, average annual ground temperature and average annual wind speed. snow accumulation and ablation over ice shelf in proximity to the Schirmacher region, shows cyclic fluctuations. The accumulation and ablation patterns are fairly dependent on temperature variations in ice shelf region. Other local factors, including albedo and global parameters, which affect regional climate may also contribute in the snow accumulation patterns. Icebergs exhibit considerable variation in their morphological characters including size, shape and disintegration pattern. A general northward shift of first sighted icebergs is observed in the last three decades. The northward shift appears to match with the trend of overall increase in surface air temperature along this part of Southern Ocean. Icebergs that have covered longer distances are highly weathered and distributed between 49°S to 66°S latitudes whereas tabular ones occurring close to Antarctic coastal area / shelf. There are two distinct zones of iceberg concentration, separated by an iceberg free zone. Continuous shift in the position of icebergs towards NNE direction between 50°S to 54°S latitudes has been concluded. Studies were carried out in the permafrost region of Schirmacher Oasis with the entire observation zone of 1 m thickness lying within the active layer. it is observed that the mean temperature decreases with depth and the range of temperature at 100 cm depth varies between -16° C and +2°C during the period of observation. However, the difference between mean temperatures at 60, 80 and 100 cm depths is very small. The immediate change (same day correlation) with respect to the surface is maximum at the upper level and becomes less with depth. The amplitude of temperature fluctuations also shows a gradual declining trend with the depth. A predictive relationship with the surface temperature can be formulated for deeper levels of permafrost, while the near-surface levels were observed to be influenced by surface fluctuations too quickly to permit any prediction.
It has been established that the ice thickness over the sea near new India Bay in the northernmost part of the cDML, varies from 28 m to 125 m within a distance of 30 km. Towards the east of Schirmacher Oasis, the ice thickness varies from 0 m to 700 m and grounding line was detected at a depth of 340 m. Maximum ice thickness in this area has been detected to be 900 m. A subsurface elevated rocky structure of about 500 m length and 30 m height has been observed. The total volume of ice in the new India Bay region is calculated to 3 3 be 7240 km which is equivalent to 6154 km water Iassuming 0.85 as uniform density of ice. The interface along the northern
margin of the Schirmacher is established knowing its continuation towards the east and west of this Oasis was more crucial for this study. The Antarctic ice sheet acts as a repository of past climatic transformations and together with the ice shelf. The study of thermal profiling shows that the variations in the polar cold front penetrated up to a depth of 25m. Beyond it, the temperatures remained uniform throughout the year. The warmest temperatures were recorded at the bottom of the glacier. The density profiling of the glacier shows that the density of topmost layers of firn is around 0.4g/cm3 whereas the blue ice in its first appearance shows a density of 0.86g/cm3. At the deeper level blue ice has an average density value of 0.91 g/cm3. The zone of temperature-inversion is observed between 25m and 30m. Beyond this depth zone, the temperature gradually rises. The δ18O values from the ice core showed clear summer maxima and winter minima throughout the length of the core, with values ranging from −20 to −37‰ whereas δD values ranged from −150 to −293‰. Annual accumulation rates at the core site calculated based on the summer peaks in δ18O record (19052005) and density of snow at respective section, ranged from 110 kgm−2 a−1 to 528 kg m−2 a−1. The (SEMEDS) study revealed several siliceous and carbonaceous microparticles, showing variation in shape and composition. The volcanic particles are enriched in silica, compared to the continental dust particle. The morphology and major element chemistry of the particles suggest their origin from volcanic eruptions as well as continental dust. The occurrence of organic and inorganic particles which bear relation to volcanic eruption and continental dust implies significant environmental changes in the recent past. It is reported that tephra related to Augung (1963) and Krakatau (1883) volcanic eruptions harbor microbial cells. Sea salt ion data indicate a significant additional contribution of chloride ions compared to sea water values, possibly through atmospheric scavenging. The δ18O records reveal that the more negative δ18O values were coeval with several events of increased NO3 concentrations, suggesting enhanced preservation of NO3 during periods of reduced air temperatures. The δ18O records also revealed a significant warming of 2.7°C for the past 470 years, with a warming of ~0.6°C per century. Comparison of NO3 and 10Be data of the South Pole ice core suggested that temporal changes in NO3 are controlled by fluctuations in solar activity in the past. Nitrate records along with sulphate and oxygen isotope records in the ice core revealed that the temporal variability in nitrate records in Antarctic ice core are influenced by complex processes of production, accumulation and 18 preservation of atmospheric odd nitrogen species. The δ O data suggests the influence of El Niño Southern Oscillation (ENSO) in this region. During the El Niño events there is an associated strong upper level advection which brings in moisture and heat from the mid-latitudes into the cDML region causing larger accumulation and atmospheric conditions warmer than the local mean which predominantly influence the summer temperature and hence the δ18O record. The combined influence of El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) was seen on surface air temperatures in this region mainly during the austral summer seasons from 1989 to 2005. Analysis of oxygen isotope data from ice cores shows sudden increase in δ18O value over the minimum at different levels, which indicates a warming and deglaciation phase. At least four such events have been observed. GPS data were collected at different sites and analyzed to estimate the site coordinates, baselines and velocities. Horizontal velocities of the glacier sites lie between 1.89±0.01 and 10.88±0.01 ma-1 to the northnortheast, with an average velocity of 6.21±0.01 ma-1. The principal strain rates provide a quantitative measurement of extension rates, which range from (0.11±0.01) x 10-3 to (1.48±0.85) × 10-3 a-1, and shortening rates, which range from (0.04±0.02) × 10-3 to (0.96±0.16) × 10-3 a-1. In a related study, the movement of ice sheet was also observed on year long basis through one polar winter. The vector movement of the glacier helps in bulging forward in the snout area of Dakshin Gangotri glacier. These extra bulged parts of the snout break down and melt away from the main glacial body during the polar summer.
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