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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

,



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