RV Sonne Cruise Report Tonga Rift Cruise No

RV Sonne Cruise Report Tonga Rift

Cruise No. SO263

01.06.2018 – 27.06.2018, Suva, Fiji – Suva, Fiji

Haase, K.M., Beier, C., Bach, W., Kleint, C., Anderson, M., Büttner, H., Dede, B., Diehl, A., Ernst, D., Funganitao, C., Giguere, T., Gonzales Porras, M.A., Günther, T., Hüttich, D., Krumm, S.H., Leymann, T., Meierhoff, I., Moje, A., Monien, P., Murdock, S., Nowald, N., Peters, C., PlanerFriedrich, B., Ratmeyer, V., Reuter, C., Reuter, M., Rubin, K., Schade, T., Schleifer, B.K., Schönhofen, M., Sopke, S., Storch, B., Ücker, M., Türke, A., Wilckens, F.

GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg

2018

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018

Table of Contents 1 Summary 2 Participants 3 Research Program 4 Narrative of the Cruise 5 Preliminary Results 5.1 Underway Hydroacoustics 5.2 Remotely Operated Vehicle (ROV) QUEST 4000 5.3 Narrative of ROV dives 5.3.1 Igneous ROV dives 5.3.2 Geological mapping and description of hydrothermal sites 5.4 Petrology 5.4.1 Sampling and analytical methods 5.4.2 Preliminary results, petrological observations and interpretations 5.5. Geochemistry of fluids and plumes 5.5.1 Sampling methods 5.5.2 Analytical methods 5.5.3 First results 5.6 Biology 5.6.1 Hydrothermal Vent Macrobiology 5.6.2 Microbiology 5.6.3 Hydrothermal symbiosis 5.6.4 Colonization experiments and protist culturing 5.7 Hydrothermal plume detection by MAPRs and CTD 5.7.1 CTD and MAPR data – first results 5.8 Expected Results 7 Station List SO236 8 Data and Sample Storage and Availability 9 Acknowledgements 10 References 11 Appendices

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Summary The research program of RV Sonne cruise SO236 Tonga-Rift aimed at improving our understanding of the igneous, hydrothermal, and tectonic processes that occur during island arc and back-arc formation. During the cruise we focused on (1) the Niua arc volcano, (2) the seamounts south of Niua, (3) an arc and fore-arc stratigraphic profile, (4) the Niuatahi caldera, and (5) the North East Lau Spreading Centre as the main sampling and research targets. We performed 17 dives using MARUM ROV QUEST 4000, 62 TV grabs, 22 volcanic rock corers, 19 CTDs and performed 11 hydroacoustic surveys. Hydrothermal plumes were determined and investigated using the CTD and Mini Autonomous Plume Recorders (MAPRs) attached to selected TV grab, CTD and rock corer deployments. Hydrothermal activity was found at Niua North and South and at the southern and northern caldera rim of Niuatahi along the caldera ring fault and at the Maka volcanic edifice along the NELSC. Hydrothermal plumes and fluids were sampled using the CTD and isobaric gas tight (IGT) fluid samplers attached to the ROV Quest. The igneous and sulfide samples in the northern Tongan area display a unique variability of compositions ideally suited to address several scientific questions related to subduction initiation and the evolution and ascent of melts in subduction zones. Samples from the North East Lau backarc environment allow the determination of the processes of melting and the interaction between arc and backarc melting zones. Sulfides and their coexisting fluids will allow to quantify and investigate the elemental fluxes in hydrothermal systems hosted in island arcs. Biological investigations focus on the hydrothermal vent communities and the interaction with the host rocks and fluid sources. Zusammenfassung Das Arbeitsprogramm der FS Sonne-Ausfahrt SO263 Tonga Rift war im Wesentlichen auf das Verständnis der magmatischen, hydrothermalen und tektonischen Prozesse ausgerichtet, die bei der Bildung von Inselbögen und Backarcs eine Rolle spielen. Im Rahmen der Ausfahrt konzentrierten sich die Arbeiten auf (1) den Inselbogenvulkan Niua, (2) die Inselbogenvulkane südlich von Niua, (3) je ein stratigraphisches Profil der Inselbogen- und ‚Forearc’kruste, (4) die Niuatahi Caldera und (5) das North East Lau Spreading Centre. Es wurden insgesamt 17 Tauchgänge mit dem MARUM ROV QUEST 4000, 62 TV Greifer, 22 Vulkanitstoßrohre und 19 CTDs, sowie 11 hydroakustische Profile gefahren. Hydrothermale ‚Plumes‘ wurden mittels CTD und Mini Autonomous Plume Recorder (MAPRs) untersucht, die an ausgewählten TV Greifer-, CTD- und Vulkanitstoßrohrstationen mitgefahren wurden. Anzeichen für hydrothermale Aktivität wurden bei Niua Nord und Süd, am südlichen und nördlichen Calderarand Niuatahis und entlang des NELSC am Maka-Vulkan gefunden. Hydrothermale Plumes und Fluide wurden mittels CTD und IGT-Sampler beprobt. Die magmatischen und sulfidischen Proben aus dem nördlichen Bereich Tongas werden Rückschlüsse auf wissenschaftliche Fragestellungen erlauben, die sich im Wesentlichen um die initiale Bildung von konvergenten Plattenrändern und die Entwicklung und den Aufstieg von Schmelzen in 1

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 Subduktionszonen, sowie der damit einhergehenden hydrothermalen Aktivität dreht. Anhand der Proben aus dem Bereich des North East Lau backarcs können außerdem die Schmelzprozesse und die Interaktion zwischen Inselbogen und Backarc Vulkanismus untersucht werden. Die gewonnenen Sulfidproben und die koexistierenden Fluide werden zudem einen wichtigen Beitrag zur Bestimmung der Elementflüsse in Hydrothermalsystemen an Inselbögen geben. Die biologischen Untersuchungen werden sich auf die Zusammenhänge zwischen den hydrothermalen Vent-Communities und den Gesteinen und Fluiden konzentrieren.

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 2 Participants Name Prof. Dr. Haase, Karsten Prof. Dr. Bach, Wolfgang Dr. Kleint, Charlotte PD Dr. Beier, Christoph Dr. Günther, Thomas Dr. Krumm, Stefan H. Schleifer, Bernd K. Schönhofen, Milena Storch, Bettina Prof. Dr. Rubin, Kenneth Diehl, Alexander Dr. Monien, Patrick Sopke, Stefan Dr. Türke, Andreas Ernst, David Moje, Annika Wilckens, Frederike Peters, Christian Prof. Dr. Planer-Friedrich, Britta Meierhoff, Ingo Murdock, Sheryl Giguere, Thomas González Porras, Miguel Àngel Ücker, Merle Dede, Bledina Dr. Anderson, Melissa Dr. Ratmeyer, Volker Büttner, Hauke Hüttich, Daniel Leymann, Tom Nowald, Nico Reuter, Christian Reuter, Michael Schade, Tobias Funganitao, Cardinia

Discipline Chief Scientist Water-rock interactions Fluid and water chemistry Petrology/Geochemistry Petrology/Geochemistry Petrology/Geochemistry Petrology/Geochemistry/Technician Petrology/Geochemistry Petrology/Geochemistry Petrology/Geochemistry Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling Fluid/gas/water sampling (Micro)biology (Micro)biology (Micro)biology (Micro)biology (Micro)biology Hydroacoustics ROV ROV ROV ROV ROV ROV ROV ROV Observer

Institution GZN, FAU UB, MARUM JU GZN, FAU GZN, FAU GZN, FAU GZN, FAU GZN, FAU GZN, FAU UHawaii UB, MARUM UB, MARUM UB, MARUM UB, MARUM JU JU JU WWU UBAY UBAY UVIC UVIC MPI MPI MPI GEOMAR MARUM MARUM MARUM MARUM MARUM MARUM MARUM MARUM MLNR

GZN, FAU

GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany

WWU

Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Germany

UB

Fachbereich Geowissenschaften der Universität Bremen, Bremen, Germany

MARUM

Zentrum für Marine Umweltwissenschaften, Bremen, Germany

JU

Jacobs University, Bremen, Germany 3

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 UHawaii

School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Hawai‘I, USA

UBAY

Fakultät für Biologie, Chemie und Geowissenschaften, Universität Bayreuth, Germany

UVIC

University of Victoria, British Columbia, Canada

MPI

Max-Planck-Institut für Marine Mikrobiologie, Bremen, Germany

GEOMAR

Helmholtz-Zentrum für Ozeanforschung, Kiel, Germany

MLNR

Ministry of Land and Natural Resources, Kingdom of Tonga

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 Research Program The research program of SO263 Tonga Rift had the main objective of sampling fluids, rocks and biological specimen and mapping the northern Tonga arc and backarc volcanic edifices. During and after the cruise we aim to test the following hypotheses with our working program: •

The isotopic signature of the subducted Louisville seamount occurs north of the islands of Tafahi and Niuatoputapu and is introduced gradually at ~4 Ma. We will use the trace element and isotope geochemistry of samples from Niua volcano, the island arc volcanoes to the south, and the arc stratigraphic profile to determine, whether the unique Pb-isotope signature of the subducting Louisville seamounts is present in the northern Tongan arc samples.

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The basement of the Tongan arc consists of a series of sheeted dykes with a depleted geochemical signature comparable to that of normal mid-ocean ridge basalt. We will use trace element and Sr-Nd-Pb isotope data of samples from the fore-arc profile to test whether the fore-arc had evolved from a normal, depleted oceanic crust to a more depleted mantle wedge composition with enriched signatures in the fluid-mobile elements with time.

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The island arc displays a systematic temporal evolution with an increasing depletion of the High Field Strength Elements and enrichment in fluid mobile elements. The geochemistry of samples from the arc profile combined with data from the Niua volcanic edifice will be used to develop a stratigraphic history of the evolution of the arc. Much of the compositional change between Niua, the seamounts south of Niua, and the arc profile may also be related to rollback of the subducting slab to the east. This will be correlated with geochemical changes observed in the volcanoes situated at different distance to the active subduction.

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The Niua volcanic edifice displays a systematic temporal evolution from the more mafic samples exposed on the northern and eastern flanks and the silicic lavas exposed on the central edifice. Major element and trace element geochemistry of whole rocks, glasses and minerals will be used to determine the origin of the silicic melts and the timescales over which these changes occur.

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Silicic melts at Niua and Niuatahi form by fractional crystallisation and assimilation of material from deeper levels of the arc crust. Major element and trace element geochemistry of the whole rocks, glasses and minerals sampled will reveal whether the large volumes of dacites erupted at Niuatahi and the pumiceous silicic lavas at Niua form by similar processes and to what extent the eruption of the distinct lava types is controlled by their geodynamic setting, i.e. does the distance to the active subduction control lava composition? The assimilation of island arc crust will be evident from trace element, radiogenic and stable isotope geochemistry. The arc and fore-arc profiles will provide a unique dataset for potential assimilating endmembers.

•

The occurrence of As sulfides at Niua results from stronger degassing of magmatic fluids whereas less degassing leads to different sulfides and fluids at Niuatahi. We will use the geochemical composition of the As-rich sulfides sampled at Niua and the fluid 5

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 data of the co-existing fluids to determine the origin of these apparently extreme sulfides. By comparing the compositions of the Niuatahi and Niua sulfides and host rocks, we will be able to develop a model for the transport of As and other volatile elements by magmatic and hydrothermal fluids in the shallow island arc crust. •

Boninitic melts may not be representative for arc initiation but may also be present in the backarc and may thus provide constraints on the geodynamic interpretation of boninitic melts. Geochemical analyses of the samples from the stratigraphic profiles and the mafic Niua lavas will be used to determine whether these lavas are geochemically restricted to a certain geodynamic environment.

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Changes in melting regime along the North East Lau spreading center are correlated with distance to the propagating spreading axis in the south. We will use major element, trace element and U-series isotope geochemistry of glasses sampled along the NELSC and samples from diagonal ridge to determine whether changes in the regime of melting can be observed as a function of distance to the arc, i.e. can the impact from fluid-flux melting versus decompression melting of normal depleted mantle be quantified?

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Hydrothermal plume signals can be used to constrain the hydrothermal element input and exchange between the oceanic crust and hydrosphere. We will use the composition of fluids sampled in-situ using unique gas-tight fluid samplers (Seewald et al., 2002) and CTD to quantify the water-rock exchange ratios and contribute to the understanding of fluid chemistry in island arc environments.

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Disequilibria, which are critical for chemosynthetic life are strongly tied to mixing of chemical reduced hydrothermal vent fluids with ambient seawater, interaction of seawater with basement, volcanic degassing, or a combination of these processes. We will use computational simulations of the fluid and water data to understand how metal solubilities are affected by volcanic and hydrologic processes in island arcs.

•

Hydrothermal vent communities, e.g. scale worms are unique to the Tonga systems as opposed to those commonly observed in the Mariana arc system. Genetic investigations of scale worms sampled in the Niua volcanic field will reveal whether the Tonga and Mariana vent communities share a common ancestor or whether the two communities have evolved separately.

In general, the sampling strategy was based on the multibeam surveys of SO263 and previous cruises on a daily basis. The sampling was preferentially done by Remotely Operated Vehicle (ROV MARUM QUEST 4000) and TV grab to ensure consistent and accurate sampling as well as structural and geological control of the sampling. We also successfully performed volcanic wax corer (VSR) sampling in the vicinity of the NELSC. During the TV grab and CTD sampling we used Miniature Autonomous Plume Recorders (MAPR) devices provided by the Pacific Marine Environmental Laboratory of NOAA. These recorders of turbidity, EH and temperature were aimed at detecting potential hydrothermal plumes in the water column in the vicinity of northern Tonga.

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 4

Narrative of the Cruise (Haase, K., Beier, C.)

A delegation of scientists from the GeoZentrum Nordbayern of the Friedrich-AlexanderUniversität Erlangen-Nürnberg and the entire Remotely Operated Vehicle (ROV) QUEST 4000 team arrived on the 29th of May and started installing the ROV and the TV grab onboard RV Sonne on the 30th of May. The majority of the scientific party joined on the 30th of May 2018 and the entire scientific party boarded the vessel on Friday, the 31st of May 2018. During port stay the installations for the ROV, the TV grab (TVG) and the volcanic wax corer (VSR) were done and the labs were prepared for operations at sea. On Saturday the 1st of June, RV SONNE left the port of Suva at 9:10 am and reached the open sea through a coral reef only a few minutes later with moderate seas and wind (Fig. 1). Heading SW from Suva into the open sea through the Fijian islands we steamed towards the NW for 44 hours into the working area at ~173°W and ~15°S. The scientific program started with hydroacoustic profiles after leaving Fijian territory in the night from the 1st to the 2nd of June. Steaming through increasing swell and winds we arrived in the working area on the 3rd of June and started untangling the ROVs winch cable from 8 am into the early evening hours prior to running a water column CTD station and three successful TV grabs in the vicinity of Niua South volcano during the early hours of the 5th of June (Fig. 1 and 2). The TV grabs contained several ten’s of kg’s of pumiceous, young lava. A fourth grab was unsuccessful as a result of technical problems. The morning of the 5th of July was used for additional ROV winch cable operations before the CTD was used for a Tow-Yo followed by four successful TV grabs in the morning containing both pumiceous felsic and basaltic lava. We started a short hydroacoustic survey and an additional vertical CTD and Tow-Yo in the morning of the 6th of June. At 2 pm on the 6th of June the ROV (dive #428) was lowered to the ocean floor, unfortunately experiencing hydraulic problems shortly after reaching the bottom which was covered by inactive and active black smoker chimneys. After the ROV was back on deck for additional maintenance we performed a vertical CTD profile and further Tow-Yos before deploying four TV grabs along the western and northern rim of Niua volcano. These TV grabs contained both pumiceous felsic lava as well as mafic pillow lavas and glass. From midnight on the 7th of June we continued our hydroacoustic survey across Niua volcano before starting ROV QUEST operations (dive #429) on the morning of the 7th of June at the hydrothermal field of Niua South. The sampling of sulfide and hard rock samples, biological specimen, and hydrothermal fluids commenced during the daylight hours of the 7th of June, but had to be abandoned as a result of a hydraulic ROV failure. Four successful TV grabs from south to north at Niua volcano recovered numerous mafic and felsic samples. A hydroacoustic survey south of Niua was conducted followed by two CTD Tow-Yos in the early morning hours of the 8th of June. During the afternoon two very successful TV grabs recovered two large black smoker pieces along with numerous biological specimen. Three TV grabs in the vicinity of Niua volcano yielded large amounts of mafic lava blocks. The early morning of the 9th of June was used to perform a hydroacoustic survey of the area east of Niua before reaching the ROV diving position at Niua South. After minor technical ROV difficulties the dive #430 started after lunchtime and successful fluid, biological and rock sampling was carried out. During the early evening of the 9th we sampled a seamount SW of Niua using the TV grab. This sampling brought on deck a massive carbonate sample. A second grab in the vicinity failed due to technical problems and a 7

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 hydroacoustic survey was performed during the night hours until the morning of the 10th. During daytime of the 11th of June, we performed ROV dive #431 in the white smoker fields of Niua North with fluid, biology and rock sampling before testing the TV grab during the early evening hours. The TV grab was successful but further testing revealed that the issue of water impacting on the connecting box between the ship’s cable and TV grab had not yet been solved. Thus, we had to terminate further TV grabbing and continued with a hydroacoustic survey during the night. On the 11th of June, we revisited the Niua South hydrothermal field during QUEST dive #432 and successfully recovered the biological traps, sampled fluids, rocks and performed a photo mosaic of an almost ten-meter-high sulfide chimney for biological investigations. Two vertical CTDs during the evening at the Hades and Prometheus hydrothermal fields at West Mata volcano only revealed a weak hydrothermal plume signal. A hydroacoustic survey was performed in the early morning hours of the 12th of June at Niua North before starting ROV dive #433 at Niua North. The dive aimed at investigating the white smoker areas and performing biological sampling in the Mussel Mania field. During the night, we performed 5 TV grabs on the seamounts south of Niua and recovered a number of pumiceous and mafic lava samples before continuing a short hydroacoustic survey. During the 13th of June ROV QUEST (dive #434) performed a stratigraphic sampling profile west of Niua aiming at the temporal evolution of the island arc. The 20, mostly mafic samples recovered from this section will provide unique insights into the evolution of the island arc crust. The night and early morning hours of the 14th of June we finalized sampling of the seamounts south of Niua performing five TV grabs recovering igneous rock samples and sediments before heading to the southern part of Niuatahi caldera volcano (formerly referred to as ‘Volcano O’) where ROV dive #435 targeted the hydrothermal field. Successful sampling of black smoker fluids, biological specimen and sulfide samples along with few lava samples from the active smoker field continued during daytime of the 14th prior to commencing TV grabs on the southern rim of Niuatahi. These TV grabs variably recovered lava blocks hosted in sediments, fresh, glassy block and dacitic pillow lavas and volcanic sulfides. During the early morning hours of the 15th of June we performed a CTD on the southern edge of Niuatahi before heading to the North East Lau Spreading Centre (NELSC) where we successfully recovered volcanic glass samples from seven stations using the wax corer. ROV dive #436 was lowered during the early morning of the 16th of June and we continued our dive along the southern rim of Niuatahi in the hydrothermal field sampling fluids, biological specimen, sulfides and lava samples, interrupted by a short safety drill. The ROV dive had to be terminated during the early afternoon due to technical problems and we continued with four TV grabs on the western and northern flank of Niuatahi recovering numerous fresh, glassy dacitic lava samples. Three CTDs were conducted during the early night hours of the 17th of June prior to ROV dive #437 during the daylight hours targeting an additional hydrothermal smoker field on the southern caldera rim of Niuatahi. Following this RV Sonne headed to the northern caldera rim and volcanic ridge north of Niuatahi performing three successful TV grabs that yielded a number of fresh and glassy samples closer to Niuatahi and loose sedimentary material including pumiceous pieces some 10 km north of Niuatahi. During the night, we transited to the fore-arc North-East of Niua, where we performed dive #438 on the 18th of June and stratigraphically sampled 26 igneous rocks between 2295 m to 1530 m water depth before transiting back to Niuatahi. A TV grab was lowered during the night, but was aborted due to technical issues and we performed a CTD Tow-Yo at the northern part of Niuatahi volcano. On the 19th of June, we started ROV dive 8

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 #439 at lunch time at the northern caldera rim of Niuatahi after technical difficulties with the ROV winch system. During the dive, several active smokers were sampled for fluids and sulfides. During the night, five wax corer stations were conducted along the southern section of the NELSC and ROV dive #440 of ROV QUEST on the 20th of June targeted the hydrothermal vent field in the northern part of the caldera. Fluids, sulfides and biological specimen were recovered. During the night, we targeted the central part of the NELSC using the volcanic wax corer sampling fresh volcanic glasses on the six stations sampled. Dive 110_ROV (dive #441) on the 21st of June targeted the southern hydrothermal field of Niuatahi and the southern caldera wall of Niuatahi recovering fluid and geological sample material. During the night we performed four TV grabs along diagonal ridge a seamount east of the NELSC. A CTD was lowered during the early morning of the 22nd of June before the ROV (dive #442; 116_ROV) started diving close to Maka volcano along the NELSC. We sampled fluids, biological and geological samples prior to starting TV grabs along the NELSC and at two seamounts East and West of the spreading axis, respectively. During the early morning of the 23rd of June we performed an additional vertical CTD in the vicinity of the Maka hydrothermal field prior to commencing the final ROV dive (dive #443; 122_ROV) of cruise SO263 approaching the Maka hydrothermal field from a southern direction sampling a number of lava flow fronts prior to sulfide, fluid and biological sampling. During the night, four TV grabs on three of the southern seamounts were performed recovering a number of mafic igneous samples before the final wax corer stations were conducted during the 24th of June. During the afternoon of the 24th of June until the 25th of June midnight we conducted a final hydroacoustic profile west of the NELSC before heading to Suva. RV Sonne arrived at Suva, Fiji on the 27th of June 8 am at docked on the berth at 8:55 am. 176˚E

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Figure 1: Shiptrack of RV Sonne during SO263 Tonga Rift. Map kindly provided by the WTD of RV Sonne.

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Figure 2: Overview of working areas targeted during SO236. Squares refer to Figures 3-6.

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Preliminary Results

5.1

Underway Hydroacoustics (Anderson, M.O., Bach, W.)

Surveys with the hull-mounted KONGSBERG EM122 MBES multibeam echosounder system (MBES) in deep water were conducted as part of the night work program. The EM122 MBES deep-sea system operates with 11.25 to 12.5 kHz. On-board R/V Sonne, a beam width configuration of 1° (across-track) by 0.5° (along-track) is installed. A swath angle of up to 150 degrees and a maximum coverage of 5.5 times the water depth can be reached. During cruise SO263, the maximum swath width was set to 70 degrees to improve data quality, reduce the amount of noisy data at the outer beams, and increase the ping rate. Sound velocity profiles (SVPs) were calculated from results of a vertical CTD cast (station 001_CTD) and applied to the raw data during acquisition via the SIS software from KONGSBERG. Multibeam profiles during SO263 were recorded focusing on the area SW of Niua volcano, Niua volcano, the southern part of the NELSC and west of the NELSC. The bathymetry data were manually cleaned using and gridded to 30 m resolution using QPS Qimera and Fledermaus. Some of the bathymetry and backscatter details revealed in these maps will be used for regional geological and structural interpretations of the work sites. The details of the seafloor geology and petrology at these sites are presented in sections 5.4 of this report. Water column data were recorded from all surveys over apparently young volcanically active area. The data were screened with the Midwater module of the Fledermaus suite of programs to look for gas flares due to volcanic degassing. No obvious flares could be detected in the work areas. 10

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 5.2

Remotely Operated Vehicle (ROV) QUEST 4000

(Ratmeyer, V., Büttner, H., Hüttich, D., Leymann, T., Nowald, N., Reuter, C., Reuter M., Schade, T.) Technical Description and Performance during SO263 (Volker Ratmeyer, Hauke Büttner, Daniel Huettich, Tom Leymann, Nicolas Nowald, Christian Reuter, Michael Reuter, Tobias Schade) The scientific deepwater ROV (remotely operated vehicle) “MARUM QUEST 4000m” was used for the second time aboard the RV SONNE during SO263. The system is hosted and operated at MARUM, Center for Marine Environmental Sciences at the University of Bremen, Germany. The QUEST ROV is based on a commercially available 4000 m rated deepwater robotic vehicle designed and built by Schilling Robotics, Davis, USA. Since installation at MARUM in May 2003, it was set up as a mobile system specifically adapted to the requirements of scientific work aboard marine research vessels for worldwide operation. Today, QUEST has a total record of 443 dives during 37 expeditions, including this cruise. During SO263, QUEST performed 16 dives to depths between approx. 700 m and 2500 m. After initial turnout of the newly spooled umbilical during two 3800m dummy casts, dive tasks included rock and fluid sampling as well as biological sampling, high quality photographic and video documentation and online in-situ measurements of fluid temperatures around hydrothermal vents. QUEST was operated by a team of 8 pilots/technicians on a 12 hours daily basis. Close cooperation between ROV team and ship’s crew through all departments allowed a safe and routinely performed handling during deployment and recovery, as well as precise navigation, underwater positioning and data transmission during dives.

QUEST System description The total QUEST system weighs about 45 tons (including the vehicle, control van, workshop van, electrical winch, 5000 m umbilical, Launch and Recovery System, and transportation vans) and can be transported in four standard ISO 20 foot vans. Using a MacArtney Cormac electric storage winch to manage the 5000 m of 17.6 mm NSW umbilical, no hydraulic connections are necessary to host the entire handling system. The QUEST uses a Doppler velocity log (DVL, 1200kHz) to perform Stationkeep, Displacement, and other auto control functions. The combination of 60-kW propulsion power with DVL-based auto control functions provides exceptional positioning capabilities at depth. Designed and operated as a free-flying vehicle, QUEST system exerts such precise control over the electric propulsion system that the vehicle could maintain relative positioning hold within decimeters. Absolute GPS-based positioning is carried out using the shipboard IXSEA Posidonia USBL positioning system. The QUEST control system provides transparent access to all RS-232, network data and video channels. The scientific data system used at MARUM feeds all ROV- and ship-based science and logging channels into a real-time database system (DAVIS-ROV), a version of the database software commonly used aboard the German research vessels. During operation, data such as 11

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 the Sonar screen, DVL map and so forth plus most videos video including HDTV are distributed to the lab and ships Ethernet network in real-time to minimize crowding in the control van. Post-cruise data archival will be hosted by the information system PANGAEA at the World Data Center for Marine Environmental Sciences (WDC-MARE), which is operated on a longterm base by MARUM and the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven (AWI).

Scientific payloads During SO263, the following scientific equipment was used aboard MARUM QUEST: - ROV based standard tools, installed on vehicle: • • • • •

2 hydraulic manipulators for sampling and experiment handling 2 hydraulic drawers for probe and sample storage ROV starboard-side basket frame for rock sampling high temperature probe "T-Lance" with logger and online data various nets and shovels with T-handles

- SO263 specific payloads, installed on vehicle • • • •

up to 3 "Seewald" type gas tight fluid samplers with online temperature data a "Major" type titanium fluid samplers 3 5-liter Niskin bottles simple fluid pump

Telepresence Video Streaming during "Telepresence Testphase 1" Within a dedicated initiative to establish high bandwidth telepresence aboard RV Sonne and other German research vessels, advantage was taken of the ships new C-Band Antenna system together with a dedicated bandwidth of 3 and 10 Mbit upload rate booked for this cruise. A variety of tests was performed to gain experience in live video streaming of ROV underwater dive video to land, namely to a MARUM based ground station server. From there, as a successful result of the setup, finally two dives were live streamed to the public internet, with HD-ready (720p) resolution. Before the public access was allowed several dives and replays of dives could be successfully streamed on a nearly routine basis, using stable 1.5 Mbit uplink rate per stream. In addition to the streaming, a teleconference software package provided by the German research network DFN could be successfully tested for real-time audio conference in combination with live video. A delay of 3-5 seconds for both signal types was achieved, which was less than anticipated. Also, high bandwidth file-based data transfer could be tested up to 7 Mbit upload rate. We are grateful for the steady support and very close cooperation with the vessels WTD (electronics and system operator dept.) and see the success of the tests as a common result of good cooperation of all parties involved.

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 5.3

Narrative of ROV dives

5.3.1

Igneous ROV dives (Haase, K.M.)

SO263 061_ROV, Dive 434, Southern rift wall The dive started in a water depth of 1920 m at the base of the slope in thick light-coloured sediments with numerous black blocks of rock talus (Fig. 3a). The first sample (#01) recovered is a talus block at 1909 m depth consisting of fresh cpx-plag-phyric vesicular lava. The dive continued in thick sediments partly covered by gravel-sized lava talus and at 1895 m we sampled a volcaniclastic rock piece (#02) from the talus. More sediment occurs on the next portion of the slope and sample #03 at 1858 m is a loose plag-cpx-phyric basaltic lava piece. Soft light-coloured sediments continue to the next sampling site where a cpx-ol-rich lava piece (sample #04) was picked up at 1804 m from the sediment. The slope above this sampling site is gentle and covered by sediment with ripples and with occasional rock talus. At the basis of a steeper part of the slope at 1748 m depth sample #05 was recovered. This sample is a plag-cpxphyric andesite. The first apparent outcrop looked like a lava flow with slabs of rock on top and was observed at 1732 m depth. Here, sample #06 was taken and consists of dense plag-cpxphyric basalt in a grey groundmass. The slope becomes steeper and the next outcrop again looks like a lava flow where sample #07 was taken at 1726 m depth. This sample appears to be vesicular ankaramite with large ol and cpx and few smaller plag phenocrysts. More sediment covers the next portion of the slope but at 1695 m depth another lava flow was observed and sampled. Sample #08 is a fresh vesicular plag-cpx-ol-phyric lava piece. As the ROV moved further up the slope more sediments were observed until a thin platy lava flow occurred that was sampled at 1655 m depth. This sample #09 is a vesicular cpx-ol-plag-phyric basalt. After moving up another 30 m the ROV encountered the first large outcrop of lava cut by a dike. The host rock of the dike was sampled at 1626 m depth and we recovered fresh plag-ol-cpx phyric vesicular lava (sample #10). At 2015 m depth the rocks immediately next to the dike was sampled and vesicular plag-cpx-phyric lava was collected. The dike can be traced on a steep cliff to 1563 m depth where it was sampled (#12) and a relatively fresh dense plag-ol-cpxphyric piece of basalt was taken. The steep cliff continues with the angular surface of the dike in the smoother massive surface of the surrounding lava. Crevasses and larger embayments in the cliff are filled with sediments and talus but the cliff consists of a massive lava surface. Sample #13 from this surface at 1518 m depth is a vesicular ol-cpx-rich ankaramite. At 1503 m the dike was sampled (#14) again and a plag-ol-cpx-phyric dense basalt was recovered. The surrounding lava on the cliff has a rough massive surface and becomes more angular in some places. Sample #15 was taken at 1487 m depth and consists of vesicular plag-ol-cpx-phyric lava. Above the sampling site the cliff becomes a more gentle slope that is covered by thick light-coloured sediment. A massive outcrop in the sediment yields sample #16, a fresh vesicular plag-cpx-phyric lava at 1461 m depth. Large pillow lavas are observed on the slightly sedimented slope above the sampling site. More lava tubes and pillows occur higher on the slope and then a layered brownish volcaniclastic rock unit yielded sample #17 at 1449 m which consists of highly vesicular pumice. Further up the slope lava flows occur below the layered volcaniclastic unit and fresh vesicular plag-ol-cpx-phyric basalt (#18) was sampled at 1440 m depth. Above the volcaniclastic unit we sampled another ol-cpx-phyric vesicular basalt (#19) 13

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 at a depth of 1415 m. The last sample of this dive was recovered from a sediment-covered volcaniclastic unit at 1396 m depth and this rock is an ol-cpx phyric vesicular basalt (#20). (a) SO263, 061_ROV, Dive 434, Southern rift wall

(b) SO263, 094_ROV, Dive 438, Tonga fore arc

Figure 3: Overview of dive profiles 434 (061_ROV) and 438 (094_ROV) on the Southern rift wall and the Tonga fore arc, respectively.

SO263 094_ROV, Dive 438, Tonga fore arc The dive started at a depth of 2335 m (Fig. 3b) on slightly sedimented talus that was sampled (#01). The first outcrop of massive angular rock was observed and sampled (#02) at a depth of 2319 m. The appearance of this outcrop is that of dikes but the sample is gabbroic. Further up the slope became more sediment-covered but the rock (#03) recovered at a depth of 2300 m also was a dense plag-cpx-phyric dolerite. The dive continued up a slightly sedimented slope with angular rock outcrops often looking like dikes with massive appearance but often faulted and with slickensides. Sample #04 was taken a depth of 2269 m from angular massive rocks and is doleritic with an enclave of plag and cpx crystals and epidote in veins. Further up the slope numerous light-coloured veins were observed indicating hydrothermal alteration of the rocks. The next rock sample (#05) was recovered at 2248 m depth from an outcrop with massive angular rocks and is a plag-cpx phyric fine-grained dolerite, again with epidote in veins. The slope consists of massive rock with straight boundaries and dike-like appearance covered by light sediments. Sample #06 is from such an outcrop and consists of altered plag-cpx-phyric dolerite with epidote in veins. Angular rocks dominate the slope and the next sample #07 at 2181 m depth is another altered plag-cpx-phyric fine-grained dike basalt with epidote veins. More dikes with parallel strike, most likely sheeted dikes and samples #08 and #09 at 2139 m depth are plag-cpx-phyric dike rock with some hydrothermal alteration and epidote on veins. The dive continued on more dikes with angular massive surfaces and numerous white veins indicating hydrothermal alteration. Sample #10 is an altered dike rock containing plag and cpx phenocrysts. The slope is steep with thin sediment cover on angular rocks with frequent parallel boundaries typical of sheeted dikes. Also light-coloured veins of alteration are criss-crossing the rocks. The next sampled rock (#11) at 2054 m depth is an altered plag-cpx-phyric finegrained dike basalt. Light-coloured sediments with layering and abundant loose lava blocks were observed on a more gentle slope above the outcrop of sample #11. These could be either 14

RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 old talus material, heavily altered rocks or pelagic sediment. Loose material with large boulders of more massive-looking rocks was sampled above these sediments and two pieces of altered plag-cpx-phyric basalt (#12 and 13) were recovered at 2025 m depth. The slope above the sampling site consists of yellowish-white apparently heavily altered rocks. Above a distinct boundary with bright white colour we observed dark greenish-grey rocks with yellow veins of alteration. Sample #14 is from this boundary at a depth of 2007 m and is an altered grey basalt with cpx phenocrysts and calcite veins. Above the dark greenish-grey rocks with irregular and rounded surfaces (pillows?) we sampled a slope with loose rocks (#15) at 1977 m depth. Sample #15 is plag-cpx-phyric lava with crystal agglomerates to 8 mm diameter. Further up the slope we find yellowish sediments with numerous blocks of rock talus. No outcrop of lavas were found on this part of the slope and the next sample (#16) taken at 1940 m depth is an altered ankaramitic lava with large ol, cpx and smaller plag crystals. Light-coloured sediments with numerous black lava blocks continue up the slope and sample #17 is from a rounded rock that may have been in situ. This sample taken at 1915 m depth is an altered plag-cpx-phyric basalt. The dive continues across a more gentle slope covered with light sediments and rock talus. Sample #18 was taken from loose blocks in the sediment at 1873 m depth and is a moderately altered plag-cpx-phyric basalt. Large boulders of rocks in the sediment become more abundant as dive climbs up the slope and sample #19 was recovered at 1833 m depth from a talus pile. This sample consists of a grey-greenish volcanic breccia where the lava fragments contain plag and cpx phenocrysts. More yellow-greenish sediment occur further up the slope and lava blocks become more abundant. Sample #20 at 1773 m is a relativey fresh basaltic andesite containing plag, ol and cpx phenocrysts taken from what appeared to be in situ lava in the sediments. The slope is now terraced with several flat areas covered with light rippled sediments and steeper slopes with rock talus. Sample #21 of fresh dense plag-phyric dacite is taken at 1727 m depth from a talus pile of steeper portion of the slope. Above this the slope becomes more gentle and layers of cream-coloured horizontally bedded sediments, most likely of volcaniclastic origin were observed. Dark lava boulders and finer talus was sampled at 1708 m depth above the layered sediments and sample #22 is a fresh plag-cpx-phyric dike rock with fine- to mediumgrained groundmass. Above this portion with more abundant lava talus we found more sediment and then at 1695 m depth an outcrop of angular massive lava where we recovered sample #23, a plag-cpx-phyric vesicular lava. The slope continues with light sediment and lava talus, sometimes appearing to be in situ. Sample #24 was recovered from a pile of talus at 1646 m depth and consists of vesicular plag-phyric dacite. More light-coloured and often layered sediments occurred further up the slope. Another talus pile was sampled (#25) and a vesicular plag-cpx-phyric basaltic andesite was recovered. Talus on top of light-coloured sediments continued to 1530 m depth where the last sample #26 was taken. This sample is a plag-phyric dark and dense dacite with about 5% vesicles. The dive ended at this depth.

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 5.3.2

Geological mapping and description of hydrothermal sites (Anderson, M.O., Rubin K., Bach. W.)

Niua Niua is an the northernmost discrete edifice on the Tofua sector of the Tonga Arc. It is roughly rectangular in shape, with several prominent ridges and a shallow point in the north at about 650 mbsl. Although it lacks a distinct volcano shape, prior workers have samples exclusively volcanic rocks from the edifice.SO263 visited two locations on Niua with the MARUM Quest ROV.

Niua South The Niua South hydrothermal vent site is centered in a large crater complex, ~350-m wide and ~80-m deep, located at ~15°9.9’S, 173°’34.4’W (Fig. 4). It was first observed in detail on a 2012 NOAA-NSF expedition guided in part by observations provided by Nautilus Minerals Inc. (see: https://oceanexplorer.noaa.gov/explorations/12fire/logs/summary/srof12cruisereport-final.pdf). Our expedition was lucky enough to have maps, ROV dive tracks, and detailed observations from that expedition, as well as those of a subsequent expedition to the site on R/V Falkor in 2016. Several smaller craters occur both within the main crater at Niua South, and on its flanks. Geological maps were created during ROV dives 428 (Fig. 5 and 6), 429 (Fig. 7 and 8), and 432 (Fig. 9 and 10). Dive 430 was not mapped. The crater itself is dominated by ash and pebble- to boulder-sized volcaniclastic pumice (Fig. 10a), with a few outcrops of a coherent pumice forming a carapace (Fig. 10b). Hydrothermal activity occurs over a large area on the floor of the crater at a depth of ~1160–1180 mbsl, dominated by variably-oxidized sulfide chimney talus forming several large mounds rising ~10–20 m above the surrounding seafloor (Figs. 6b and 10c). The tops of the mounds are characterized by inactive chimneys up to ~10 m in height (Fig. 8a), and minor diffuse venting of lowtemperature fluids (shimmering water; Fig. 8b). High-temperature chimneys are mostly restricted to the flanks of the mounds, perhaps because there is a permeability contrast that promotes fluid flow. These chimneys range in size up to ~15 m in height, with measured vent temperatures up to 318°C (Fig. 8c). The chimney morphologies include beehive diffusers (Figs. 6a,c, 8c) and multi-spired chimney complexes (Fig. 10d). The active chimneys are colonized by microbes (forming white mats), snails, shrimp (large and small), crabs, and scale worms. Widespread low-temperature diffuse venting has resulted in cementation of the volcanic talus in the immediate vicinity of the chimney mounds, revealed by local collapse features (Fig. 8e).

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Figure 4: Geological observations made during Dives 428, 429, and 432 (Niua S), with contours from unpublished AUV bathymetry courtesy GEOMAR.

Figure 5: Geological observations made during Dive 428, station 021_ROV (Niua South), with contours from unpublished AUV bathymetry courtesy GEOMAR.

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Figure 6: Photos of geology from Dive 428, station 021_ROV (Niua S): (a) beehive diffuser chimney with putative bacterial matting and snails; (b) chimney talus; (c) black smoker diffuser chimneys. Copyright: MARUM, University of Bremen.


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Figure 8: Photos of geology from Dive 429, station 029_ROV (Niua South): (a) large inactive chimney; (c) diffuse venting of shimmering water with snails and crabs; (d) beehive black smokers that vent boiling fluids at a temperature of 318°C; (e) collapse feature in indurated crust. Copyright: MARUM, University of Bremen.


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Figure 10: Photos of geological features from Dive 432, station 050_ROV (Niua S): (a) talus slope with pumice clasts and blocks; (b) pumiceous lava with joints/striations; (c) angular chimney talus; (d) 3-spired chimney complex with minor venting of black-grey smoke. Copyright: MARUM, University of Bremen.

Niua North The Niua North vent site is located at ~15°4.8’S, 173°’34.7’W (Fig. 11). It was discovered in 2011 by dredging of molten sulfur on KM1029a, a University of Hawaii expedition funded by Nautilus Minerals Inc. (K. Rubin, pers. comm.). The site was subsequently studied by ROV in 2012 on the aforementioned SROF’12 expedition. Maps, observations, and dive tracks were generously provided to our group. Geological mapping of this site was undertaken during transects on dives 431 (Figs. 12–14) and 433 (Figs. 15 and 16). These dives were designed to cover essentially the same tracks as the SROF’12 dives. The site is currently characterized by two small pits at a depth of ~750 mbsl, associated with vigorous venting of S-rich gas (Fig. 13). In 2012, the site was venting more vigorously (including CO2 venting), and had several active pits, including one that looked to contain molten sulfur (K. Rubin, pers. comm). The substrate at the site is primarily unconsolidated volcaniclastic, consisting of pebble- to bouldersized clasts of rhyolite pumice and lava (Figs. 14a,b, 16a), based on compositional analysis at the University of Hawaii. The proportion of visible lava appears to increase near the pits, with a wall of exposed lava on the eastern margin of the southern pit. Currently, the southern pit is a nested crater, ~16 m wide and ~10–12 m deep (Fig. 13a). Beginning ~70 m downslope of this pit, there are large blocks of native sulfur, and a few patches of mussels and tube worms (Fig. 16b). On the northern and western flanks of the pit, in-situ slabby yellow sulfur flows are exposed (Fig. 14c). Venting in the pit occurs both along the top bench and within the central crater, consisting of several vents of vigorous S-rich yellow and white smoke at temperatures of up to 112°C, issuing directly from the volcanic substrate (Fig. 14d). Liquid sulfur occurs

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RV Sonne, Cruise SO263 Tonga Rift, Suva, Fiji – Suva, Fiji, 01.06.2018-27.06.2018 over a small area at the bottom of the pit (Fig. 16c). The northern pit is ~30 m wide and ~7 m deep (Fig. 13b). This pit is associated with less vigorous venting of S-rich white smoke. Sampling the fluids was not possible at this location due to poor visibility inside the crater. Adjacent to this pit is a large field of mussels, known as “mussel mania” (Fig. 16d), extending ~30 m to the north and east. Surrounding this pit are poorly-sorted, subangular to subrounded clasts of primarily pumice with minor lava, as well as white (S-rich?) sediment. Active sulfur flows were not observed at this location, unlike prior observations in 2011 and 2012.

Figure 11: Geological observations made during Dives 431 and 433 (Niua North), overlain on ship-based multibeam bathymetry.

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Figure 12: Geological observations made during Dive 431, station 047_ROV (Niua North), overlain on shipbased multibeam bathymetry.

Figure 13: Screenshot of the ROV forward-looking sonar (Kongsberg Mesotech MS1000) at Niua North: (a) ~16 m wide pit in the southern map area; (b) ~30 m wide pit in the northern map area. Field of view is 40 m, line spacing is 8 m.

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Figure 14: Photos of geology from Dive 431, station 047_ROV (Niua North): (a) clasts of rhyolite and pumice; (b) in-situ rhyolite; (c) in-situ slabby sulfur flows on the wall of the southern pit; (d) bench within the southern pit with vigorous venting of S-rich white smoke. Copyright: MARUM, University of Bremen

Figure 15: Geological observations made during Dive 433, station 054_ROV (Niua North), overlain on shipbased multibeam bathymetry.

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Figure 16: Photos of geological features from Dive 433, station 054_ROV (Niua North): (a) large block of Mncoated pumice; (b) tube worms, sulfur blocks, and pumice talus downslope of the southern pit; (c) liquid sulfur (center) and sulfur vents in the southern pit; (d) large “Mussel Mania” field near the northern pit. Copyright: MARUM, University of Bremen.

Niuatahi Niuatahi (previously known as Volcano O) is a large caldera structure in the back-arc, characterized by a down-dropped basin surrounded by a circular ridge structure and extensive dacite lava flows both within and around the caldera (Park et al., 2015; Embley and Rubin, 2018). Prior work has shown that it has a young resurgent volcanic cone in south-central part of the caldera named Motutahi (not visited on this expedition), as well as several hydrothermal vent sites discovered by Nautilus Minerals Inc. in 2007.

Niuatahi (‘Volcano O’): South-Central Hydrothermal Site This unnamed vent site located in the south-central part of the Niuatahi (formerly ‘Volcano O’) caldera occurs at ~15°23.2’S, 173°’59.9’W (Fig. 17). Geological mapping of this site was undertaken during dives 435 (Figs. 18 and 19), 436 (Figs. 20 and 21), and the first half of dive 441 (Figs. 22 and 23). The hydrothermal vents are located on the western flank of a large cone (possibly volcanic) at a depth of ~1600 mbsl, within a small offset (