grams to slope upward from south to north following the same trend of the sigma-t surfaces. This indicates that mixing and advection. Redacted for Privacy ...
AN ABSTRACT OF THE THESIS OF
SAUL ALVAREZ -BORREGO for the Master of Science Degree
in Chemical Oceanography presented on May 4, 1970 CHEMICO-OCEANOGRAPHICAL PARAMETERS OF THE
CENTRAL NORTH PACIFIC OCEAN
Abstract approved:
Redacted for Privacy
Data from the Surveyor 1968 Spring cruise were used to study
the vertical distribution of salinity, temperature, dissolved oxygen, apparent oxygen utilization, pH, alkalinity, specific alkalinity and percent saturation of calcite in two sections, one along 162°W from 35°N to 45°N and the other along 180°W from 35°N to 50°N.
Data
from this cruise and additional data from the Surveyor 1968 Fall
cruise, YALOC 66 cruise (summer) (Barstowetal,
,
1968) and
Boreas cruise (winter, 1966) (SlO reports, 1966) were used to study
the distribution of salinity, temperature, apparent oxygen utilization, preformed phosphate and depth on the sigma-t surfaces of 26, 8 and 27.3 in an area between 35°N and 52°N and 162°W and 155°E.
In both sections the vertical distribution of the physico-chemical
parameters is such that in general there is a tendency for the isograms to slope upward from south to north following the same trend
of the sigma-t surfaces. This indicates that mixing and advection
along the sigma-t surfaces play an important role on the distribution of these parameters. AOU data from YALOC 66 cruise (summer) compared to that
from Surveyor 1968 Spring cruise suggest that aeration by mixing, eddy diffusivity and conductivity takes place to more than 500 meters depth at about 50°N. It also suggests that the changes of organic
primary production at the euphotic zone during different seasons of the year may affect to a great extent the AOU distribution on the
26. 8 sigma-t surface and to a very small extent on the 27. 3 sigma-t surface. The direction of flow suggested by the AOU distribution on the
26. 8 and 27. 3 sigma-t surfaces was compared to that indicated by the acceleration potential contours on the ci' = 125 cl/ton and
=
80 cl/ton surfaces drawn by Reid (1965). The disagreements were
explained in terms of mixing and possible gradients of primary
production at the sea surface. On the 26. 8 sigma-t surface a southward flow connecting the westward flow south of the Aleutian
chain and the eastward flow farther south, between 175°E and 180°W
is suggested by the AOU distribution but not by the acceleration potential contours. If the circulation pattern at this density
surface is similar to that at the sea surface, this linkage is very likely to be real.
Chen-üco-oceanographical Parameters of the Central North Pacific Ocean by
Saul Alvarez-Borrego
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of Master of Science June 1970
APPROVED:
Redacted for Privacy Associate Professor of Oceanography in charge of major
Redacted for Privacy Chairnan of Departme4t of Oceanography
Redacted for Privacy Dean of Graduate School
Date thesis is presented
May 4, 1970
Typed by Suelynn Williams for Saul Alvarez-Borrego
With love to my parents
Pedro Alvarez-Ortega and Dolores Borrego-De-Alvarez
With affection and admiration to
Dr. Norris W. Rakestraw
ACKNOWLEDGMENTS
I thank my major professor Dr. P. Kilho Park for his guidance throughout this study. I also would like to express my thanks to the
Francis P. Shepard Foundation and the Instituto Nacional de la
Investigacidn Cientfica de Mxico for their support while working on my Master' s degree program.
I extend additional thanks to Dr. Felix Favorite for his helpful
criticisms. The discussions with Louis I. Gordon were very helpful. I also want to thank Stephen Hager, Milton C. Cissell, David S.
Ball, Jacques Pirson, Dennis Barstow, Peter Becker, the scientific personnel from the Pacific Oceanographic Research Laboratory at Seattle, Washington, and the officers and crew of the USC&GSS
Surveyor for doing all the necessary work at sea during the Surveyor 68 Spring and Surveyor 68 Fall cruises. I appreciate the help of Lynn Jones with the computer program and the comments of John Hawley and Charles H. Culberson regarding
the study of calcium carbonate saturation. I am indebted to Lynda Bar stow for her helpful comments
regarding the grammatical structure of this thesis and to Suelynn Williams for typing.
Finally, I want to express my sincere gratitude to my wife, Esthela Elsie Millan-De-Alvarez, for continuously encouraging me and for being patient while I was working on this thesis.
TABLE OF CONTENTS I,
II.
III.
INTRODUCTION. OBSERVATIONS
,
.
.
.
.
.
.
.
.
.
1
.
.
........... Temperature ...............
RESULTS
Salinity
.
.
.
.
.
,...... .
.
.
.
........... . Dissolved oxygen (oxyty) ........... Sigma-t
.
.
pH.................. ................ Alkalinity
IV.
DISCUSSION ................ Salinity, temperature and sigma.-t
9
12
12 15 19 19
24 26
30 30
Dissolved oxygen (oxyty), apparent oxygen utilization (AOU), pH, and preformed phosphate
.
.
.
Alkalinity and specific alkalinity .........
............ ........ ........ ................
42 61
Percent saturation of calcium carbonate with respect to calcite SUMMARY
.
.
.
.
.
.
.
.
63 75
SUGGESTIONS FOR FUTUIE WORK
78
BIBLIOGRAPHY
80
LIST OF FIGURES
Page
Figure 1
Location of the stations used in this study, and Ocean Station
PH.
1C
Vertical distribution of S%o (lefti and T°C (right' at 162°W.
13
3
Vertical distribution of
14
4
Distribution of S%o on the sigma-t
=
26.8 surface.
16
5
Distribution of S%o on the sigma-t
=
27.3 surface.
17
6
Vertical distribution of T°C at 180°W.
7
Distribution of T°C on the sigma-t
=
26.8 surface.
2C
8
Distribution of T°C on the sigma-t
=
27. 3 surface.
21
9
Vertical distribution of sigma-t (left) and oxyty
2
S%o
at 180°W.
13
(right) at 162°W,
22
10
Vertical distribution of sigma-t at 180°W,
23
11
Vertical distribution of oxyty at 180°W,
2S
12
Vertical distribution of pH at 162°W.
2&
13
Vertical distribution of pH at 180°W.
27
14
Vertical distribution of alkalinity at 162°W.
28
15
Vertical distribution of alkalinity at 180°W.
29
16
Temperature-salinity (T-S) diagram for a series of stations across the Subarctic Boundary (after Park, 1966).
17
30
Typical salinity (up) and temperature (down) structures at Ocean Station 'P" (after Dodimead etal. 1963). ,
31
LIST OF FIGURES continued Page
Figure 18
Depth of the sigma-t
=
26.8 surface.
37
19
Depth of the sigma-t
=
27. 3 surface.
38
20
Vertical distribution of AOU at 162°W.
45
21
Vertical distribution of AOU at 180°W.
46
22
Vertical distribution of AOU at one station of Surveyor 1968 Spring cruise and one of YALOC 66 (summer) cruise.
47
Preformed phosphate distribution with latitude on the sigma-t = 26. 8 and sigma-t = 27. 3 surfaces from YALOC 66 cruise (Barstowetal, 1968) and Boreas cruise (Boreas Data Report, Sb, 1966).
51
24
Distribution of AOU on the sigma-t = 26. 8 surface.
55
25
Distribution of AOU on the sigma-t = 27. 3 surface,
56
26
Acceleration potential on the surface where 125 cl/ton (after Reid, 1965).
58
23
,
27
Acceleration potential on the surface where 80 cl/ton (after Reid, 1965).
=
=
58
Two AOU isograms with the "suggested" and actual direction of flow indicated by arrows.
61
29
Vertical distribution of specific alkalinity at 162°W.
62
30
Vertical distribution of specific alkalinity at 180°W.
64
31
Vertical distribution of the percent saturation of calcium carbonate with respect to calcite at 162°W.
68
28
LIST OF FIGURES continued
Page
Figure 32
33
34
35
Vertical distribution of the percent saturation of calcium carbonate with respect to calcite at 180°W,
69
Vertical distribution of pH at four stations of Surveyor 1968 Spring cruise.
71
Vertical distribution of AOU at four stations of Surveyor 1968 Spring cruise,
72
Vertical distribution of the percent saturation of calcium carbonate with respect to calcite at four stations of Surveyor 1968 Spring cruise.
73
CHEMICO-OCEANOGRAPHICAL PARAMETERS OF THE CENTRAL NORTH PACIFIC OCEAN I, INTRODUCTION
The North Pacific Ocean has been subjected to extensive oceanographic investigations. Since the formation of the International North Pacific Fisheries Commission there has been an intensive investigation of the ecological factors that affect the distribution of the economically important marine organisms that have their habitat in this part of the ocean. A great part of these studies have dealt with physical oceanographic problems and have provided an excellent framework for any other type of study. Several authors (Dodimead, Favorite and Hirano, 1963; Reid, 1965; and others cited therein) have reviewed the literature concerned with the physical oceanography of the North Pacific Ocean, Sverdrup, Johnson and Fleming (1942) mentioned that in the North Pacific Ocean one encounters a Subarctic Water mass at about 50°N characterized by an average temperature between 2° and 4°C, According to them salinity at the surface may be as low as 32, 00%o but increases to approximately 34, 00%o at a depth of a few hundred meters and below that depth increases slowly to about 34. 65%o at the bottom,
On the basis of data collected in the Northwestern Pacific from 1929 to 1954 Hirano (1958) was able to obtain general information on distributions of temperature and salinity as well as the flows and their circulations in this region for spring and summer, Tully and Dodimead (1957), using data in the Northeast Pacific, identified Subarctic and Subtropic Waters, They showed that the
principal differences were in the properties and the structure of the upper layers. The Subarctic Boundary between these two water masses is generally identified by a nearly 'crertical isohaline of 34.
O%o
which
extends from the surface to a depth of about 200 to 400 meters (Dodimead, Favorite and Hirano, 1963).
North of the boundary in the Subarctic Region, the salinity is
at a minimum at the surface and increases with depth. The water column is characterized by a permanent halocline between approximately 100 and 200 meters depth above which a thermocline develops
in summer and vanishes in winter, South of the boundary in the
Subtropic Region, the salinity is at a maximum at the surface and decreases to a distinct minimum at about 500 meters depth, In
spite of this salinity distribution the water column is stable due to
the temperature structure (Dodimead etal. , 1963), The salinity minimum of the Subtropic Region is the core of the Subarctic Intermediate water, Favorite and Hanavan (1963) defined two fronts in the North Pacific: a temperature front associated with an almost vertical isotherm of 4°C, and a salinity front associated with the isohaline of 34, 00%o, They considered the area to the north of the temperature front to be the Subarctic Region, the area between the two fronts to be the Transition Region, and the area to the south of the salinity front to be the Subtropic Region, Subarctic waters are characterized by a temperature minimum and Subtropic waters by a salinity minimum at middle depths, But Transition waters do not have a temperature or salinity minimum, In the Western Pacific the fronts coincide and
3
form a sharp boundary, whereas in the Central Pacific they are about 300 miles apart. Reid (1965) published a monograph entitled Intermediate Waters
of the Pacific Ocean. He concluded that the Subarctic Intermediate
Water does not originate at the sea surface, because the density surface that closely corresponds to the salinity minimum zone only
occasionally intersects the sea surface in small areas off Kamchatka and the Kuril Islands. He pointed out that, even though the contact between the atmosphere and this density surface is limited, cooling, freshening and aeration are observed on it. He proposed that the
characteristics of the Subarctic Intermediate Water are formed in high north latitudes by vertical mixing through the pycnocline. That is, vertical eddy conductivity and diffusivity without convective
overturn to the depth of this density surface. According to him, this seems consonant with the known deep circulation of the Pacific Ocean which involves massive upwelling in the Subarctic Region
rather than overturn to intermediate depths. Dodimead etal. (1963) defined hldomainsu for the Subarctic
Region. Applying the geostrophic method they studied the system of
currents at the surface, ZOO-meter and 500-meter depths, with an assumption that a level of no motion exists at 1000-meter depth. However, they recognized that this level may be in appreciable motion in some parts of the region and recommended further studies on this problem.
McAlister, Favorite and Ingraham Jr. (unpublished manuscript) studied the influence of the Komandorskie Ridge on the surface and
4
deep circulation in the Northwestern Pacific Ocean. They stated that,
although transport in deep waters may be significant, the dynamic topography provides a good representation of surface flow and that
the direction of the subsurface flow to 2000 meters depth is generally
the same as at the surface. The surface circulation relative to 1000-meter depth in the
extreme Western Pacific consists of the warm saline Kuroshio Current which moves northward along the Japanese Islands with the main flow turning eastward at about 36°N. This water continues
eastward as the North Pacific Current to about 150°W where it
moves southward. Part of the Kuroshio continues northeast to about 40°N where it meets the cold southward-moving less saline
current, Oyashio, which is present along the eastern side of the Kuril and northern Japanese Islands. At the confluence of the two currents extensive mixing occurs both horizontally and vertically. These mixed waters continue eastward as the "West Wind Drift"
with a slight northerh component carrying it to about 45°N in the
vicinity of 180°E. From there it continues eastward to approxi-
mately 300 miles from the Washington-Oregon coasts. Here the
water divides--part turns south to form the California Current, and a small part intrudes into the area off the coast of Vancouver Island and then moves southward along the coast; the remainder
flows north into the Gulf of Alaska, The part of the Oyashio Current that does not actively mix with the Kuroshio Current moves northeastward to within 60 miles of the Aleutian Islands in the vicinity of
l80°E. Most of this water moves east as the Subarctic Current. It
5
eventually flows into the Gulf of Alaska and around the Alaskan gyre,
making its return in the strongly westward flowing Alaskan Stream along the southern side of the Aleutian Islands. The remainder of
the water forms a gyre centered at about 50°N, 165°E. The water at the edge of the gyre mixes with the water of the Alaskan Stream, moves westward to the end of the Aleutian chain and then a portion
of it enters the Bering Sea. While some of this water flows northward to the Arctic Ocean through the Bering Strait, the main branch forms a cyclonic circulation which flows southward along the Siberian
coast. One part of this main branch becomes the East Kamchatka Current and the other is absorbed into the cyclonic gyre present in the central Bering Sea (Dodimead etal.., 1963). Favorite (1965) concluded that the Alaskan Stream is
continuous as far westward as 170°E where it divides sending one branch into the Bering Sea and one southwestward to join the
eastward flowing Subarctic Current at about 165°E.
According to McAlister et al, (unpublished manuscript) the Komandorskie Ridge marks the westernmost extent of the Alaskan
Stream as a well-defined feature. The ridge appears to inhibit
any deep circulation. However, it does not seem to have an effect on the Kurashio-Oyashio flow, They also indicated that in a north-
south vertical section of temperature the deepening of the isotherms near. the. Aleutian Trench suggests that the Alaskan Stream extends
to 4000 meters depth. Although some studies have been accompLished in the North
Pacific Ocean with reference to its chemical oceanography, much
needs to be done. Detailed rationalized studies of the overall
patterns of vertical and horizontal distribution of physico-chemical
parameters are far from being complete. Trying to determine the direction of water motion between
1 000-and 2000-meter depths in the Northeast Pacific Ocean, from the coast of America to 150°W and from 20°N to the north, Pytkowicz and Kester (1966) used apparent oxygen utilization (AOU) and pre-
formed phosphate concentrations. Their results suggest a northward motion at low latitudes and southward motion at high latitudes with a
divergence off the California coast. Park (1967) studied chemical features in a section near 170°W, from 35°N to 50°N. In a4dition to the use of the isohaline structure
of 34. 0%o to locate the Subarctic Boundary, he found other surface
chemical parameters are also useful. Near the boundary, within a distance of one degree of latitude apart (60 miles) surface phosphate concentrations changed from 0.5 to 0.9 M, pH from 8.27 to 8.18,
and the silicate concentration from 3 to 19 pM. However, since these chemical boundaries were observed during summer, the same
may not be true for other seasons of the year. The surface distributions of phosphate and silicate from 35°N to the Aleutian chain and from 162°W to 180°W, had been studied
in spring (Park, Hager, Pirson and Ball, 1968). Both silicate and phosphate were higher at the northern part with a maximum of 2.0ii.M
phosphate and 30 p.M silicate at 49°N, 173°W. They did not give a
definite explanation of the mechanism responsible for this, mention-
ing the possibilities that the occurrence of phosphate and silicate
maxima may be either a product of the upward divergence of the
subsurface water or that the high nutrient area has a very late production in April-May, or both phenomena coupled0
Anderson, Parsons and Stephens (1969) studied the nitrate distribution in the Subarctic Northeast Pacific Ocean and suggested that the maintenance of high nitrate concentrations over much of the
area is due to the same factors that Park et al. (1968) mentioned, In the book entitled "Chemistry of the Pacific Ocean," the members of the Institute of Oceanology of the U. S. S. R, Academy
of Science discussed the distribution of temperature, salinity, oxygen and nutrients in the Subarctic Region. They included several
graphs of these parameters showing the overall picture, both vertical and horizontal, at different locations and depths. pH and specific alkalinity are also shown and discussed for the overall patterns at different depths.
Sugiura (1965b) studied the distribution of reserved (preformed)
phosphate in the surface waters of the Subarctic Pacific Region from about 45°N to the north and in the western part of the Bering Sea. He described a mechanism by which he believes the relatively high concentration of preformed phosphate is maintained in this region. Kester and Pytkowicz (1968) examined the degree of oxygen
saturation of surface waters in the Northeast Pacific Ocean, from about 20°N to the north and from the coast of North America to
180°W. They observed large differences between winter and summer conditions such as 97% in winter and 105% in summer for some parts of the Gulf of Alaska, and 101% in winter and 105% in summer for the
sea off Baja California. They related these differences to photosyn-
thesis, warming of the surface waters, and upwelling, To explain the distribution of the chemical parameters that are affected by the biological activity, it is very important to know how
the organic primary productivity changes with the seasons of the year. Parsons, Giovando and LeBrasseur (1966) described the spring phytoplankton bloom in the Eastern Subarctic Region from estimations
of the critical depth and the depth of the mixed layer. Their description was supported by the distribution of copepods in the region during April. Organic primary production data show values of up to 1100 mg
C/m2/day during the period May-June compared with values of 200 or
less mg C/m /day during March-April, at Ocean Station P located at 50°N, 145°W (McAllister, 1962).
The purpose of this thesis is to clarify to some extent the mechanisms that are responsible for the distribution of the physicochemical parameters in the central North Pacific Ocean, giving special attention to the characteristics of the Subarctic Boundary and
the salinity minimum zone of the Subtropical Water Mass. In trying to elucidate these mechanisms I have tried to give due importance to both the physical and biochemical processes for in Nature they are
inseparable. An investigation of either one of them separately requires a high degree of arbitrariness, for although frequently one of them seems to be the most responsible process, the action of the
other is always present. Thus, both create the actual chemicooceanographical structure of the water masses and their boundaries.
II. OBSERVATIONS In
1968
a chemical-oceanographical group from Oregon State
University headed by P. Kilho Park participated in two cruises aboard the USC&GSS Surveyor, the first in April-May and the second
in September-October. The positions of the hydrographic stations
from these cruises that were used in this work are shown in Fig. 1. Detailed data from the first cruise were obtained for two sections. Determinations were made for temperature, salinity,
dissolved oxygen, pH, alkalinity, nutrients and total carbon dioxide. Data from the second cruise were obtained for five sections but only three or four stations per section had dissolved oxygen, pH, alkalinity and nutrients determinations. pH was determined by a glass-electrode technique described by Park (1966). A Beckman pH meter, Model 7600, expanded scale, was used to measure the pH values. Dissolved oxygen and alkalinity were determined according to the manual of Strickland and Parsons (1965).
Salinity was measured by a Hytech inductive salinometer
manufactured by the Bissett-Berman Corporation, San Diego, California.
For plotting salinity, temperature, apparent oxygen utilization (AOU) and preformed phosphate on sigma-t surfaces, additional data were taken from YALOC Wyatt,
1968)
66
(Barstow, Gilbert, Park, Still and
and Boreas (SIO reports,
1966)
cruises. The location
of the stations from these cruises that were used in this work is also shown in Fig. 1, For the YALOC 66 and the Boreas cruises the
0 S
a.
500
A £
A
A A
0 0 0
ft
A A
A
LA
400.)
Sta. + Ocean lip"
0 A
A A A 0
.
0
Os
300
o YALOC66(Summer) 200
SURVEYOR 68 (Spring) A SURVEYOR 68 (Fall) A
BOREAS (Winter 66) 1500
1600
170°
I
180°
1700
160°
3.500
130°
Fig. 1. Location of the stations used in this study, and Ocean Station "P".
I] 3.20°
0
11
procedures from the Strickland and Parsons' manual (1965) were also used to determine dissolved oxygen concentrations and inorganic phosphate. Salinity was determined by a Hytech inductive salinometer
on Boreas cruise, and an inductive salinometer manufactured by
Industria Manufacturing Engineers Pty. Ltd., Sydney, Australia, was used on YALOC 66.
12
III. RESULTS Salinity
a) Vertical distribution From the section along 162°W (Fig. 2), it can be seen that the Subarctic Boundary exists at 40°30'N, if we use the 34. 0%o vertical isohaline to define it. At 180°W (Fig. 3) the boundary was found at 44°N. At 180°W the isohaline of 34. O%o is shown to be almost
vertical from the surface to a depth of 200 meters. It tends to be horizontal in deeper waters and forms a tongue of irregular shape southward into the Subtropic Region as far as about 36°30'N. At 162°W the 34.
O%o
isohaline is almost vertical from the surface to a
depth near 250 meters, This isohaline then moves northward where it forms a tongue that extends to about 42°30'N. It then turns south
to deeper waters. A very distinct salinity minimum is shown in both sections- along 162°W it was found near 300 meters depth at 45°N and near
600 meters depth at 35°N; at 180°W the minimum clearly begins to
appear near 45°N at a depth of about 200 meters and then irregularly increases in depth southward getting to 500 meters depth at 35°N. In general, the salinity minimum zone was found to be deeper at 162°W than at 180°W.
Between 600 and 1000 meters depth the isohalines show no
general trend south of the boundary in both sections, but they
gradually rise at the north as it has been observed in other studies.
.-
- I-'-
39°
'
410
37°
C
,
1°
390
:'
1OC
1OC
200
-
33.s--
20C
300
300
400
J400
34.9-..
500
600
500 SAL.MIN.
o 600
4-)
700
700
800
800
900
900
1000
1000
Fig. 2. Vertical distribution of
S%0
M&MI.
.
.
4
(left) and T°C (right) at l62°W.
4;3°
14
0
100 200
300
400 500
600
700
900 1000 1100
1200 1300
1400 1500
1600 1700 1800
Fig. 3. Vertical distribution of S%0 at 180°W.
I5
Below 1000 meters the isohalines show irregular distribution all the way from 35°N to 50°N at l80°W (Fig. 3). b) Distribution on surfaces of sigma-t = 26.8 and sigma-t = 27.3
On the sigma-t surface of 26.8 (Fig. 4), the salinity is shown to vary with latitude from 34. 0 %o at about 40 °N to 33. 6 %o at about 50°N.
The variation with longitude is very small, decreasing
slightly from east to west with exception of the northern part,
from about 48°N to the north, where the change is irregular. On the sigma-t surface of 27. 3 (Fig. 5) the salinity changes slightly with latitude, from 34. 3 %o at about 40°N to a minimum of about 34. 25 %o and increasing again to 34. 3 %o in the northern part
near 50°N.
Temperature
a) Vertical distribution An almost vertical isotherm of 11° C, sinking from the surface to 200 meters depth, is shown at the boundary in the section along 162°W (Fig. 2), and another of 9°C from the surface to 100 meters depth is shown at the boundary in the section along 180°W (Fig. 6).
In general the isotherms ascend from south to north--the farther
north, the greater the slope. Along 180°W near 48°N, the 4°C isotherm is almost vertical from the surface to about 500 meters, which is the extreme case in the two sections. Along l80°W a temperature minimum was observed from 48°N to the north, This minimum existed at a depth of 300 meters at 48°N and at 200 meters
600
500
400
300
20°
.';'J-
4.OV
Fig. 4.
JU
17O'
10'
1500
Distribution of S%0 on the sigma-t = 26.8 surface.
1400
1300
1200 0'
50°
F
I
