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Pacific wi,t~,I' ",,:'i,:,

Minimum ,~p¥:~r'

UNIVERSITY OF WASHINGTONDEPARTMENT OF OCEANOORAPHYSeattle, Washington 98195

Technical.Report No. 289

Some Chemical and Physical Properties of the Eastern TropicalNorth Pacific with Emphasis on the Oxygen Minimum Layer

by

Louis A. Codispoti

National Science FoundationContracts GA-I0084 and GA-24875

Office of Naval ResearchContracts Nonr-477(37) and

N-00014-67-A-Ol03-00l4Project NR 083 012

Reference M73-64October 1973

Francis A. RichardsPrincipal Investigator and

Assistant Chairman for Research

IT-

Reproduction in whole or in part is permittedfor any purpose of the United States government

-... t. ~,

iii

ABSTRACT

This report is basically an atlas presenting diagrams and charts oftemperature, salinity, oxygen, nutrient, and relative baroclinic currentdata for the eastern tropical North Pacific. Special emphasis is on theoxygen deficient layer in this region and a number of the charts constitutean isentropic study of this layer. Two of. the included properties,nitrate deficits and equivalent nitrate, are particularly appropriate fo!'investigations dealing with denitrification in these waters, and themethods for calculating them are described.

A temperature-salinity, temperature-oxygen diagram presents evidencefor significant respiration at depths of about 800 m.

iv

ACKNOWLEDGEMENTS

It is impossible to mention everyone who contributed to this report.However, those who made special contributions include the following: ShirleyPatterson, Dorothy Lowman, Susan Sugai, Dr. F. A. Richards, and MSsrs.J. Anderson, R. Cromoga, A. Devol, D. Doyle, and T. Owens.

Financial support was provided by the Office of Naval Research undercontracts NONR-477(3) and N-OOOl4-67-A-Ol03-00l4, and by the NationalScience Foundation under grants GA-l0084 and GA-24875-Al.

" I

v

TABLE OF CONTENTS

!

ABSTRACT . . · · . · · · · . · · · ·AC~iOWLEDGE}mNTS · · · · · · · · · . . · .LIST OF TABLES · · · · · ·LIST OF FIGURES. · · ;I· · · · · · ·i .~..

IliTRODUCTIONI

· · · · . . · · · · . . · .DATA SOURCES · · . . . . · · · . . · · · ·EXTENT OF THE OXYGEN DEFICIENT ZONE. •

VERTICAL AMMONIA DISTRIBUTIO~.

TEltPERATURE-SALINITY !A.l~D TE~1PERATUP.E-OA~r,EN DIAGRM1S •1

TE}1PORAL VARIATION DIAGRAJ.'1S.

iii

:tv

vi

vii

1

1

1

1

': 7

:J.O

VERTICAL SECTIONS••••••

f1ISENTROPIC" ANALYSIS CHARTS

· c... . . . . . . 15

NITRATE DEFICITS

REFEREi~CES • • •

..' .I

• • I.

!

.36!

139

vi

LIST OF TABLES

!

1. Cruises sponsored by the University of Washington. • • •

p~'geI I

'2

..

2. Cruises sponsored by agencies other than the Universityof lvashington • • • • • • • • • • .• • • • •

3. Surfaces chosen' for "isentropic" analysis.

3

2[4iii

I

:11

vii

LIST OF FIGURES

Pape

1. Extent of the oxygen deficient region in the easterntropical Pacific. . • • • • • • • • •

2. Dissolved oxygen distribution along l12°W

4

5

3. Vertical ammonia profiles•••.• 6

4. Temperature-salinity relationships in the study re~ion n

5. Temperature-salinity and temperature-oxygen diagram for the27.3 a surface. • • • • • • • • • • • • • • • • 9

T

6. Variables versus depth for three stations near the southernboundary of the oxygen deficient region • . • • • • • • • • • • 11

7. Variables versus depth for three stations in the interior ofthe oxygen deficien t region • • • • • •• ••••• • • 12

8. Variffi>les versus depth for two stations in the interior of theoxygen deficier. t region •••••• ••••••

•9.

10.

Variables versus depth for two stations near the northernboundary of the oxygen deficient re~ion • •• • .

:litrite distribution a1onp, 112°\01 •

I

• ! 13I

I

• 14

• 16

11. Nitrate deficit distribution along ll2°W • . • 17

12. (A) Temperature, (B) salinity, and (C) reactive silicatedistribution alon~ 112 oW. • • • • • • • • • • • • .'18

13. (A) Temperature and (n) salinity sections from data collectedduring Thomas G. 'l'honrpson. Cruise 1. • • • • • .• • • • • • 19

14. (A) Reactive phosphorus and (B) reactive silicate sections fromdata collected during Thomas G. Thompson Cruise 1 • 20

15. Relative baroclinic currents along l12°W . . . . . . · · 21

16. Relative baroclinic currents adjacent to Baja California • . . · · 22

17. Equivalent nitrate (A) and salinity (B) on the 25.5 a surface · · 26T

13. Equivalent nitrate (A) and salinity (E) on the 25.8 a surface · · 27T

19. Equivalent nitrate (A)9 and salinity and nitrite (B) on the26.1 a surface. . • • • • . • • ••.• . ••.... 28

1"

viii

Pa~e

20. Equivalent nitrate (A), and salinity ·end nitrite. (B) on the26.4 a surface. •• • • • • • • • • • 29

T

21. Nitrite on the 26.4 a surface.T • • 30

22. Equivalent nitrate (A), and salinity and nitrite (B) on the26.6 a surface. · · · · · · . . · · . · · · · · · · · 31

T

23. Equivalent nitrate (A) , and salinity and nitrite (B) on the26.8 a surface. · · · · · · . . · · .. · · · · · · · · 32

T

24. Equivalent nitrate (A) , and salinity and nitrite (B) all the27.0 a surface. · · · · · · · · . · · · · 33

T

25. Equivalent nitrate (A) and salinity (B) on the 27.3 a surface. · 34T

26. Equivalent nitrate (A) and salinity (B) on the 27.5 a surface. · 35T

27. NO; ANOH, NO; ANO~f II and Cline and Richards' (1972) nitrate

deficits versus depth at two selected stations · · · . . · · · 37

28. NO; ANOM versus Cline and Richards' (1972) nitrate deficits (A)

and ~O; ANOM II versus Cline and Richards' nitrate deficits(B~ 38

•

INTRODUCTION

The diagrams and charts comprising the bulk of this 'report areprimarily from a thesis on denitrification in the eastern tropical NorthPacific Ocean (Codispoti, 1973). Some of the less useful figures havebeen excluded, some have been updated, and a new figure showing therelative baroclinic currents in the region of the California Undercurrenthas been added. .

This report has been prepared because the included figures form auseful atlas for some'properties in the oxygen minimum layer of the easterntropical 'North Pacific Ocean. Due to space limitations, only a fractioncould appear in forthcoming publications dealing with the main results ofthe denitrification study.

DATA SOURCES

Except for Figure 1 which is redrawn from Reid (1965), the data sourcesfor this report are listed in Tables 1 and 2. Additional information on the~zomas G. Thompson cruises is available in Dugdale and Healy (1970), Universityof Washington (1970), and Lowman and Codispoti (1973).

EXTENT OF THE OXYGEN DEFICIENT ZONE

Most of the evidence indicates that oxygen concentrations must beless than ~O.l ~/liter (~10 ~g-atoms/1iter) before denitrification can beobserved in marine environments (Brandhorst, 1959; Richards, 1965; Thomas,1966; Fiadeiro and Strickland, 1968; Cline and Richards, 1972). If sulphatereduction has not begun but denitrification is ~roceeding, the term oxygendeficient is used to describe such environments. Figures 1 and 2 ~ive someidea of the horizontal and vertical extent of the oxygen deficient layer inthe eastern tropical North Pacific. The vertical extent also decreases withincreasing distance from the coast.

VERTICAL AMMONIA DISTRIBUTION

TIle purpose of Figure 3 was to present additional evidence in supportof Thomas' (1966) contention that ammonia does not appear to be the majorend product of Initrate reduction and denitrification in the eastern tropicalHorth Pacific.

-----------------To be rigorous, the ammonia concentrations should have been expressed asug-atoms/1iter of ammonia nitrogen instead of }.Ig-atoms/1iter of ammoni,a.The reader should note that this type of "shorthand" has been used through­out this report. For example, reactive silicate in }.Ig-atoms/1iter shouldreally be expressed as reactive silicate-silicon in lJg-atoms/liter~ nitratein ~g-atoms/1iter should be nitrate-nitrogen in }.Ig-atoms/1iter; etc.

2

Table 1. Cruises sponsored by the University of Washington.

Vessel and Cruise No. Year

R/V Thomas G. Thompson Cruise 1 1965

R/V Thomas G. Thompson Cruise 26 1968

R/V Thomas G. Thompson Cruise 35 1969 }}

R/V Thomas G. Thompson Cruise 37 1969 }}

R/V Thomas G. Thompson Cruise 46 1969-70}}

R/V Thomas G. Thompson Cruise 66 1972 }

Sources

University of Washington, Dept.of Oceanography, Tech. Report249, and the National Oceano­graphic Data Center

University of Washington, Dept.of Oceanography, Tech. Report250, and the National Oceano­graphic Data Center

University of Washington, Dept.of Oceanography, Tech. Report284, and the National Oceano­graphic Data Center

3

Table 2. Cruises sponsored by agencies other than the University ofWashington.

Vessel and Cruise No. orNODC Ref. No. Year Source

R/V Horizon

R/V Hugh M. Smi th

R/V D.S. Jordon

R/V D.S. Jordan

R/V D.S. Jordan

STEP-I 1960

C~tiise 1959T9.-S9-2I!

Cruise 12 1967

CALCOFI 1968Cruise 6804

i

CALCOFI 1968Cruise 6806

~Scripps In~titution of Oceanography

u.s. D~pt. of the Interior, Fish andWildlife Service

EASTROPAC (Natiqnal Uarine FisheriesService, Scripps Institution ofOceanogranhy, Inter-American TropicalTuna Commission)

California Cooperative OceanicFisheries Investigations (ScrippsInstitution of Oceanography)

California Cooperative OceanicFisheries Investigations (ScrippsInstitution of Oceanography)

~IODC 90-0589

NODC 31-1072

NODC 31-1166

1959 National Oceanographic Data CenterI

1966 National Oceanographic Data Center

1967 National Oceanographic Data Center

R/V Proteus Cruise 22 1970 Stanford University

R/V Proteus Time-Series 1969-71 Stanford UniversityStation

R/V Shoyo Maru Cruise 13 1963-64 Inter-American Tropical TunaCommission

"

R/V Te Vega

R/V Te Vega

R/V Te Vega

R/V Te Vega

C+"uise 13I

Cruise 14

Cruise 16

Cruise 17

1967

1967

1967

1968

Stanford University

Stanford UniverRity

Stanford Universiity

Stanford University

R/V Cayuse Cruise C7002D 1970 Ore~on State University

4

Figure 1. Extent of the oxygen deficient region in the eastern tropicalPacific. The shaded area indicates oxygen concentrations ofless than 0.25 ml/1iter on the 125 c1/ton thermosteric anomalysurface. This surface is at ~ 400 m (after Reid, 1965).

5

STATIONSOr-6_-,.7__of---_...,.IO__'r2 'r3 1_5---_17---_18~1 ....9-...:;.20.:........:2;;.;...'

--<5

~

\<5 " · '--- ....... \

· · · ..J-~--------------~~-~

.----- -40

100

600

,----, ...... ,1 )" 5

I I ,I <5 I >5 II · / I I, /~ /

, ,*"I I .,"

_ 400 i \" /~ II ...... *"Q) ,.tI,Q) "'"E 15001---........::~_I__--.l.__.L...- ......... 1____--L ___J_l.--_l-!...___J

:I:Ii: Or---T-"--,...---,.--y-------r----..-----..-----------lLJC

..

1500'---...L...---'-_---L__J.- --L .1...-__....J.. ---J"--L----J_--'

,wo

1200

I 1100

i6e7_a_

loe12-

13-

I~-I,.leeZo.21-

110·

100

Figure 2., 0

Dissolved oxygen distribution along 112 W. Concentrations arein ~g-atoms/liter and were determined by the colorimetric method(Broenkow and Cline, 1969). The data are from Thomas G. ThompsonCruise 46.

6

3

100011000°'--..........---..........--_...... ()D

90°

AMMONIA Lug-atoms/liter)I 2

°r~rr----;-~:::!ib;:t:.-'---I

1500 L......--...L...,.;:=-6-_....a....__.........__--L.__---'__--J

110° 1000 90°f/) 280~

G)-Q)

E

J:: 20~a..

wTGT CR .:

0STA 65

10°

Figure 3. Vertical ammonia profiles.

7

TEMPERATURE-SALINITY AND TEMPERATURE-OXYGEN DIAGRAMS

Figure 4 is a I conventional temperature-salinity diagram for the regioninvestigated in the denitrification study. Except for station 71 which isto the north of the: oxygen deficient layer, the diagram indicates considerableuniformity in the layers below 1\1200 meters and in waters with a values

Texceeding 1\126.0. Figure 5 is a temperature-salinity, temperature-oxygendiagram for the aTI- 27.3 surface. This surface is near the core of thesalinity minimum and is generally found at a depth of about 800 meters.When the above factors are considered, this diagram presents strong evidencefor significant in situ changes in non-conservative properties at the depthof the a m 27.3 surface.

T

8

••

800

• TE VEGA CR. 16OCT- NOV 1967

• TGT eR. I

1000 900

1100 800

J""l'T"oo;:-:r----,----,--------,3QO

•

4

16lLJa::::J

~a::lLJa..~lLJI-

uo-

2L...-------I.-------.........---------------~33.5 34.0 -34.5 35.0

SALINITY (%0)

Figure 4. Temperature-salinity relationships in the study region. Somesurface layer values have been excluded.

o

o

9

6.0 .....--...:..------,.....-------~--------,

4.0 --. .L- ..L- ~

34.4 34.5 34.6 34.7SALINITY (%0)I 2

OXYGEN (ml / liter)

Figure 5. Temperature-salinity and temperature-oxygen diagram for the27.3 a surface.

T

10

TE~ORAL VARIATION DIAGRAMS

These diagrams (Figs. 6-9) were designed to investigate temporalvariations in nitrate, nitrite, and dissolved oxygen in the oxygendeficient region. Often, the agreement appears to be within theprecision of the methods, particularly in the deeper layers. This suggeststhat a knowledge of the concentrations of non-conservative properties inthe deeper layers for a given area could provide a rapid means for estimatingdata quality.

I

.,

o

........

•o

TGT CR.ISTA 58 II NOV 65 TGT CR. 35

0••STA 28 8MAR 68TGT CR 26STA 44 12 FEB 68

NICARAGUA--="~

60L.- ..A

o

o

• 1309....5;...o_W -....__...;;,;85°

N

o

DISSOLVED OXYGEN (mg-atoms/liter)

0.1 0.2 0.3 0.4 0.5

NITRATE Lug-atoms/liter) NITRITE (ug-atoms /1 iter)

0 10 20 30 40 0 I 20

200

400

r· .?600

en'- t>.Q)-Q) 800 ~E

0

:I:1000 ? • ~~

a..w 00

1200 ~

0

"1400•

0

1600

1800

Figure 6.. Variables versus depth for three stations near the southern boundary of the oxygen deficientregion.

. MEXICO

I04°W19°'r.-·..;...~----------~N '.' .

-:.:::..: ..-.:.. : ... ~ .

TGT CR. I "'~;'''.;.:.:., .STA 65 3 DEC 65 . ···~':l ..:.. :.::-. . .. .

\\~~: ~R. :~:~~:~.;;:.\STA 75 27FEB 68

13°-------------........••

DISSOLVE D OXYGEN (mg-atoms / liter)

0.1 0.2 0.3 0.4 0.5

•,.•

0 •0

.,p0

• ·0

NITRITE tug-atoms /1 iter)

012

NITRATE Lug-atoms/liter)

a 10 20 30 40a

o·••200 e.tO

eo•• 00

400 -.00

101

600 •en •'- ••cv+-cv 800 ••E

•:I:

1000l- ••a..w •0

1200 ••

1400

1600

1800

Figure 7. Variables versus depth for three stations in the interior of the oxygen deficient region.

'.

...

....w

1000

..,. .-:.... : MEXICO·

..;:. ': ...:TGT CR. 37STA 27 18 MAY69

iTGT CR. 26STA 7 15 JAN 68

13°'------------.........

o•

DISSOLVE 0 OXYGEN (mg-atoms / liter)

0.1 0.2 0.3 0.4 0.5

.. 0

.. 0o ..

o •

NITRITE tug-atoms/liter)

2

NITRATE Lug-atoms/liter>

10 20 30 40 0

200~.fl

• 0.. 0·0

400 iD

6J

600 &>en'-OJ~

OJ 800 .0E

:I:1000 2I-a...

w0

.01200

1400 0A

1600

1800

Figure 8. Variables versus depth for two stations in the interior of the oxygen deficient region.

O'TGT CR. 46STA 8 20 DEC 69

18° ~

IISOW25Or-------.-~-w"'""---~~--

N

o•

•

•o

DISSOLVE D OXYGEN (mg-atoms / liter)

0.1 0.2 0.3 0.4 0.5

NITRITE (Jig-atoms/liter)

a I 2

NITRATE (Jig-atoms/liter)

a 10 20 30 40O-----,....-~--~---,----,

200

400 • 0

·0

600 ~fJ)~ 0Q)- •Q) 800E

0

:I: •I- 1000 0

Cl.W0 •

1200 0

•1400

0•1600

1800

Figure 9. Variables versus depth for two stations near the northern boundary of the oxygen deficientregion.

15

VERTICAL SECnONS

These sections (Figs. 10-16) give some idea of the distribution ofnitrite, nitrate deficits, temperature, salinity, reactive silicate,reactive phosphorus, and the relative baroclinic currents in portions ofthe region emphasized in the denitrification study (Codispoti, 1973).The nitrate deficit ,(Fig. 11) is an estimate of the amount of nitrateconverted to free nitrogen by denitrification. The calculation and validityof this term will be briefly discussed later on in this· report and in moredetail in a forthcoming publication (Codispoti and Richards, in prep.).

The relative baroclinic current sections (Figs. 15 and 16) appear topresent a reasonable picture of the currents. For example, nitrate deficittransports computed'with the aid of these currents (and the use of reasonableestimates for the vertical and horizontal diffusive transports) yielded adenitrification rate which compared favorably with an independent estimate(Codispoti, 1973). These currents are, nevertheless, subject to the normallimitations of such I representations. For example, the barotropic mode wasneglected; the net westward transport in Figure 15 seemed somewhat low(Codispoti, 1973); and some significant baroclinicity may remain at the depthsof the reference levels (Reed, 1970).

For the shallow area in Figure 16, Helland-Hansen's (1934) methodwas used to obtain the relative baroclinic currents. These values comparedreasonably well wit~ the currents obtained by using the deepest referencelevels possible in the water column.

Two shallow stations (maximum sampling depth = 370 m) were occupied tothe north of station 6 (Fig. 15). These stations were not included in theoriginal calculations, but a preliminary analysis indicates a strong netflow towards the east.

16

\8 19 20 2\17STATIONS

13 15121087

12()O

. .. .. ",:-- ........... _-~- ..._. .:.-----_._---- ... "",:- ............. "" • ..,. . 0.1_.. - - - • o' ...)-;::#:--.,.----.-- ...... - ...... . >0..l ... __ --r -- .14P'- --- - -:--~ - --.""

,. • iloilo :-- ."". __ ...; __ '" - ,:: •

• _Ol''''''~' I•.." - - . - - >2.0 : I. ..""",, >0.1' . . I·

/"" 0.49 1.0 2.0 . ,/ ;0.77 : 1

. ( I':', J\ I .... "",/ " /,..... '.... ",,"'". ~""-... ",,.;'.... ""...._-

6O--........--,.....-........----,....-------,,..------.----,.----......---T-......----,

1200

100

200

300

400fI)..Q)

Q)E 500

:I:....00-

W0

Figure 10. Nitrite distribution (in ~g-atoms/liter) along ll2°W. The dataare from Thomas G. Thompson cruise 46.

17

STATIONSo6;...._~__;.-_...:;_----:;- :.:;:13 ....:.:;: --T --:..r__........,r-~21

&>0

~~~...'-~~------~~ 4~-~:-•• • c;::::;....-. .. . . ...

110" 100"

6e7_e_

loe12-

13-

IS-I~

lee10· 20e 10"21-

120" 110· 100"

<4

Figure 11. Nitrate deficit (NO; ANOM II' in ~g-atoms/liter) distribution

along 112oW. The data are from Thomas G. Thompson cruise 46.

18

18 19 20 2117STATIONS

13 25 15128 25107

I -I

I 10- ! T I T

~~ · ! ! 12 --r 1· · · · · ·II ·· -10 · · · . ·· · · 9~ · -

· -... ...&.8 · · · -- 7 -l- · ... · · · · · -· · · -6-- • · • - · ·l- · · · · · · · -

· · · · · 5 · ·l- · · · · · · · · · --4 -l- · · · · · · · · · -

(A) -I- ...36 I .. I , I

6o

600

400

200

800

1400

1200

1000

0

34.80

34.6

-;n 0.50:~

Q,)

Q;EJ: 1000I-Q.

· (B)W 1200 ·0

1400

15e

1-'-

18e

10· 20e10021e

1200 110" 100·

Figure 12. (A) Temperature (OC), (B) salinity (%0)' and (C) reactivesilicate distribution (~g-atoms/liter) along ll2°W, ThomasG. Thompson cruise 46.

."

19

STATIONS71 70 69 68 67 16 • 64 63 62 61 60 ~ 51 57

14t--200 12

IIIi8 --76 --.5-

4

3 -3-

(A)110· lDO"' 90"

feua:;E~~Q.lL! 0" 0"0 110" 100" 90-

STATIONS72 71 70 69 68 fiT 66 65 64 63 62 61 60 !l9 3 56 57

0

>348·200

34.8 .--34.7-.:.----- . --

o ---346 • -a.-.-0o _ ....

800 0<34.6

1000

1200

1400

(B)

Figure 13. (A) Temperature (Oe) and (B) salinity (%0) sections from datacollected during Thomas G. Thompson cruise .1.

I

..

20

----------::-----..0.-3__.a---------:.._~

2.5-_-=- - -

60 !l962 61STATIONS66 ~ 64 6368 67

I

70 6971

1400

O"L---'--_L--....L...-...... O·110· 100" go.

60 !>962 61STATIONS66 6!l 64 63

=:-----=----:===--...:..-_--=---_._­-------".----.....:.-:==:---.--

...............--------~-.-':

~._-

~----..----:-----...t.___-a..--800

72 71 70 69 68 67

0~~~~~~~:::::r:~==r910200 • 30--....__:-----+---_....:.__ :400

I~

1200

1000

( B)

Figure 14. (A) Reactive phosphorus (pg-atoms/liter) and (B) reactivesilicate (pg-atoms/liter) sections from data collected duringThomas G. Thompson cruise 1.

21

" ~-~,. .7" ,.""-~.... /.

i' :'. (\. ,II· J

!.(I ,\. IV

400

1200

1000

Figure 15. Relative baroc1inic currents along ll2oW(lOOO decibar referencelevel). Contour lines are in em/sec. Solid lines indicateeastward flow and dashed lines indicate westward flow.

NN

-12

••

••

••••

•o

••

•••

•

•

•

•

STATIONSI 2 3 4 5 6 7 8 10 II

o,----j~-~.O::_...-.-~-[lT~--r--.......,,.-"""'w:-l~--t'--r- .........--r-:::,--......--~---:-.........,r:---r-r--~-...--+:;....- -44... . ...........@: .... /~E"2,,"""·~· ••••••• ° I .... '"'' 0o •• .",.", , ••· · .. eJ ° 11"n , ~ o.

: • •• 12- : II II ~ I '\ .' °

:. • • • 8 • : II 1\ \ ~~o, 1 ". ~ ~••• • •• : I \ ,'..7r6 I J.':

• ., \ \ I I , 0

•• • • • • : \ \ "-..; 12 I , :\ :\\ I,:. • •• : \ \. ;8 • I •; . \ ,/ ,:: \ - .1·•. \. I:: \ , .

.: ,. -4'· ~.o ..... _- 0

600

200

400

800

1000

.:...: .

: • 110° • • • :~ .

.. ' •••• • ••• 0· • • • • ~.. ' ..... ..... ...-... ... ... .1200 1......--_~_--_-I-_-~_-I-_-----'------~.....:..&.4_.......-I__---.!..--L.. -L-__----1...L_....L...J

:r:i­n.Wo

Ul~

Q)-Q)

E

Figure 16. Relative baroclinic currents adjacent to Baja California (1200decibar reference level). a Southeasterly flow.s Northwesterly flow. Speeds are in em/sec and the data arefrom THOMAS G. THOMPSON cruise 66.

•

23

"ISENTROPIC" ANALYSIS CHARTS

Although these charts (Figs. 17-26) were used primarily to develop amethod for estimating nitrate deficits and to assi~t in the determinationof denitrification rates, they reveal many other interesting features.Table 3 lists the a surfaces which were selected for the "isentropic"analysis and also gIves some idea of the depth range of each surface.Nitrite values were 'contoured whenever there was a distinct manifestationof the deep nitrite imaximum (the maximum associated with oxygen deficientwaters). However, at two locations values in excess of 0.5 ~g-atoms/liter

and associated with low oxygen concentrations were found on 25.8 a surface.T

The equivalent nitrate charts represent a property. defined as follmls~

l\NO~

l\02

where NO- = equivalent nitrate,3EQUIV.

NO; = the observed nitrate concentration,

NO; = the observed nitrite concentration,

°2 = the observed dissolved oxygen concentration, and

l\NO; the ratio of nitrate produced to oxygen consumed during~ =·aerobic respiration, 16/276 (by atoms) as suggested by

2 Redfield, Ketchum, and Richards (1963).

In other words,equivalent nitrate is an estimate of the amount ofnitrate which should be present in a water parcel when aerobic respiration

I

has reduced the oxygen concentration to zero. Within a given water parcel,this quantity should be nearly constant until denitrification begins,provided that the ratio for the ~NO;/l\02 term remains close to 16/276(by atoms). 2

I

2 Because of this property, equivalent nitrate values, like preformednutrient values, can often be used to assess data quality for aerobicsubsurface water masses .

24

Table 3

Surfaces chosen for "isentropic" analysis

a'f

Thermosteric Anomaly Approximate Depth Range inthe Study Region (Meters)

25.5 249.1 40 - 120

25.8 220.6 50 - 140

26.1 192.1 50 ,- 200

26.4 163.6 100 - 300

26.6 144.6 175 - 375

26.8 125.6 300 - 475

27.0 106.7 450 - 560

27.3 78.2 770 - 880

27.5 59.3 1100 - 1350

."

25

The consensus of most recent investigators is that free nitrogen is themain end product of nitrate during marine denitrification (Codispoti, 1973).Since free nitrogen appears to be essentially conservative below the surfacelayers, areas of low equivalent nitrate values do not necessarily indicateactive denitrification sites. For example, oxygen concentrations throughoutthe 25.5, 25.8 and 27.5 0 surfaces were generally too high to expect

Ldenitrification. Nevertheless, equivalent nitrate v~lues on these surfacesdisplay a minimum in the vicinity of the oxygen deficient region indicatingthe possibility of mixing with waters from denitrification zones.

26

-

300

80"

80°goo

35.0~- .:":"'

• • ~~'.' "" " O·>350

1200

100

200

Figure 17. Equivalent nitrate in lJg-atoms/liter (A) and salinity in0/00 (B) on the 25.5 0 surface. Expected nitrate for thissurface is 32.8 lJg-at~/liter.

27

<31

31

10"

(A)

120" 90"

. 0°

a

20"

10"

(8)

120"

35.0~···1• • ! \.

• • I • .......--.....: "

.. ~:l::' . _1

100"

80°

.~

30"

: 10"

I

Figure ~8. Equivalent nitrate in llg-atoms/liter i (A) and salinity in0/00 (B) on the 25.8 a surface. Expected nitrate for thissurface is 33.6 Ilg-ato~/l1ter. !

200

100

10"

(A)

1200

1200

120"

28

.~. . ...\:-...~ .... .• \~"('33 •33---....... .. ~,'~......., "...J •

<33 .......... <33. ...._--....--. --

900 800

·100

30

Figure 19. Equivalent nitrate in pg-atoms/liter (A), and salinity in °/0.and nitrite in pg-atoms/liter (B) on the 26.1 a surface.Expected nitrate for this surface is 34.6 pg-at6ms/liter.

100

29

10"

1200

110°

34.8--):>34.8 ... .

<34.8.

34.8

100°

34.9----

90° 80°

Figure 20. Equivalent nitrate in Vg-atoms/liter (A) and salinity in Q/ oo(B) on the 26.4 a surface. Expected nitrate on this surfaceis 35.4 ~g-atoms/liter.

100

120'

1200

30

1000 goo

ir:." .

800

100

Figure 21. Nitrite (~g-atoms/1iter) on the 26.4 a surface.'t

31

," 10°. .. .

34.8-----~ :... ... .....".,. .o .. \ 0 •••

.. 34.79... ...(8 )

130°

10°

10°

36 -_o_:z:::>0° ..?~~ 0 0°

(A))2 "'-:-',

130° 120° 110° 100° 90° 80°

130° 120° 110° 100° 90° 80°

SALINITY a NITRITE.. SALINITY ONLY

• NITRITE ONLY30' SALINITY 30°

NITRITE

30'

20°

130° 1000 900 80°

Figure 22. Equivalent nitrate in lJg-atoms/liter (A), and salinity in 0/00

and nitrite in lJg-atoms/liter (B) on the 26.6 a surface.Expected nitrate on this surface is 3604 lJg-ato~/liter.

32

30°

10"

100

(B)

1200

347

.. ~;'.~.346~••

30"

Figure 23. Equivalent nitrate in lJg-atoms/liter (A), -and salinity in 0/00

and nitrite in lJg-atoms/liter (B) on the 26.8 a surface.TExpected nitrate on this surface is 38.7 lJg-atoms/liter.

".

10"

10"

(A)

(8)

120"

120"

33

1000

~'" 38,---- _.....~

" 42

1000

1000

1000

goo

goo

800

80"

3

30"

.100

.~

"

Figure 24. Equivalent nitrate in ug-atoms/liter (A), and salinity in 0/00

and nitrite in ug-atoms/liter (B) on the 27.0 a surface.TExpected nitrate for this surface is 42.5 ug-atoms/liter.

34

100

..,

300

8001000

900

.. : .::.:~~;;",:,:: :',.3455~::~' ,':

, . ' )4.53', : " 3\4.5,4• .-34.53,.' •••

>34.55 -34512

<345

)\1....

. . ... . ...34.50 .• ,

1200

20"

100

300

Figure 25. Equivalent nitrate in lJg-atoms/liter (A) and salinity in 0/00

(B) on the 27.3 aT surface. Expected nitrate' on this surface is48.6 lJg-atoms/liter.

100

(A)

>49

1200

35

<49 ..

~...

49' • . ..~.

• ~8.6 •

49

>49

1000 800

•

10"

(8)

1200

120"

: '34.57

>34.58

1100 1000

3461/

300

,Figure 26. Equivalent nitrate in ~g-atoms/liter (A) and salinity in °/0 0

(B) on the 27.5 a surface. Expected nitrate on this surfaceis 50.7 ~g-atoms/liter.

36

NITRATE DEFICITS

By averaging equivalent nitrate values in the source waters for theoxygen deficient strata a term called expected nitrate (NO; ) was determined.

EXPNitrate deficits (N03 ),3 as shown above (Fig. 11), are then calculated

ANOM IIas follows:

/

NO- ~ NO; - NO- , and3ANOM EXP 3EQUIV

NO; = NO; x 1.094.ANOM II ANOM

A more detailed discussion of the development, the reliability and therational behind the method for computing nitrate deficits is given inCodispoti (1973). Here it is sufficient to note that the above equationsused in combination with the expected nitrate values given in the figurecaptions (Figs. 17-26) will yield useful nitrate deficit estimates for thestudy region. However, the reader should be aware that the method forcalculating nitrate deficits may be slightly modified when published in itsfinal form (Codispoti and Richards, in prep.).

(2)

(3)

Figures 27 and 28 give some idea of the agreement between the abovemethod and the method of Cline and Richards (1972). These comparisons weremade using the same data employed for developing Cline and Richards' method.One disadvantage of their method is that it requires reactive phosphorusdata and is sensitive to errors and systematic differences in these data.

3 As mentioned on page 15, nitrate deficits provide a measure of theamount of nitrate converted to free nitrogen during denitrification.

."

37

- ... _-- -----

800

400

400

200

600

a600 6

800-en...C»-C» (A)E 1000-:J:~a. 00 2 14LLJC

D A

200

1000---------------------....J

Figure 27. NO; ANOM' NO; ANOM II and Cline and Richards' (1972) nitrate

deficits versus depth at two selected stations •

•

38

20.00-..~~

.\......• 15.00 xE0-a ,I

~- 10.00!::0i&::w0

5.00w (A)~0:!:::z

0.00 SLOPE = 1.400:dS R2 = 0.930 R =0.97

-5.00-5.00 0.00 5.00 10.00 15.00

NITRATE DEFICIT (Jig-atoms lliter)

20.00

-..CD~

.......en 15.00e ~

0-0,0'1

~10.00....

5::!.....w0

w 5.00(B)

~0:!:::z

0.00SLOPE = 1.280:

ell R2 = 0.930

R = 0.97-5.00

-5.00 0.00 5.00 10.00 15.00

CORRECTED NITRATE DEFICIT tug- atoms Iliter) ,'"

Figure 28. NO; ANOM versus Cline and Richards' (1972) nitrate deficits (A)

and NO; ANOM II versus Cline and Richards' nitrate deficits (B).

)

39

REFERENCES

Brandhorst, W. 1959. Nitrification and denitrification in the easterntropical North Pacific. J. Cons. Int. Exp1or. Mer 25: 3-20.

Broenkow, W. W. and J. D. Cline. 1969. Colorimetric determination ofdissolved oxygen at low concentrations. Limnol. Oceanogr. 14: 450-454.

Cline, J. D. and F. A. Richards. 1972. Oxygen deficient conditions andnitrate reduction in the eastern tropical Nor~h Pacific Ocean.Limnol. Oceano~r. 17: 885-900.

Codispoti, L. A. 1973. Denitrification in the eastern tropical NorthPacific Ocean. Ph.D. thesis, Univ. of Wash., Dept. of Ocean •. 118 p.

Codispoti, L. A. and F. A. Richards. In prep. A new method for calculatingnitrate deficits in the eastern tropical North Pacific Ocean.

Dugdale, R. C. and H. L. Healy. 1970. Physical, chemical and productivitydata from an investigation of the northeastern tropical Pacific Ocean:RV Thomas G. T'l1ompson cruise 026 (PONCHO). Univ. \~ash., Dept. Ocean.,Technical Report 250. 162 p.

Fiadeiro, M. and J. D. H. Strickland. 1968. Nitrate reduction and theoccurrence of a deep nitrite maximum in the ocean off the west coastof South America. Deep-Sea Res. 26: 187-201.

Helland-Hansen, Fj. 1934. The Sognefjord section, p. 257-274. In JamesJohnstone Hemorial Volume. Liverpool.

Lowman, D. ~t. and L. A. Codispoti. 1973. RV Thomas G. Thompson cruises035,037,046, and 066. Univ. of Wash., Dept. Ocean., TechnicalReport 284, 15 p.

Redfield, A. C., B. H. Ketchum, and F. A. Richards. 1963. The influence oforganisms on the composition of sea water, p. 26-77. In ~f. N. Hill,E. D. Goldberg, C. O'D. Iselin, and W. H. ~funk (eds.), The Sea, Vol. 2.Interscience, London.

Reed, R. K.Ocean.

1970. Geopotential topography of deep levels in the PacificJournal of the Oceanographic Society of Japan 26: 331-339.

Reid, J. L. 1965. Intermediate waters of the Pacific Ocean. The JohnsHopkins Press, Baltimore. 85 p.

Richards, F. A. 1965. Anoxic basins and fjords_ p. 611-645. In J. P. Rileyand G. Skirrow (eds.), Chemical Oceanography, Vol. 1. Academic Press,London and New York.

40

Thomas, W. H. 1966. On denitrification in the northeastern tropicalPacific Ocean. Deep-Sea Res. 13: 1109-1114.

Univ. Wash., Dept. Ocean. 1970. Physical, chemical and, productivity datafrom a surv~ of the Caribbean Sea and the northeastern tropical PacificOcean: RV Thomas G. Thompson Cruise 001. Univ. Wash., Dept. Ocean.,Technical Report 249. 224 p.

UnclassifiedSECURIT' CLASSI FICATION OF THIS PAGE (When Dete Entered)

REPORT DOCUMENTATION PAGE READ INSTRl:CTIOSSBEFORE COMPLET!~GFORM

'1. REPORT NUMBER

Technical Report No. 289·2. GOVT ACCESSION NO. 3. IItECI~IENT'S CATALOG NuMBER

")

4. TITLE (and Subtitle)

SOME CHEMICAL AND PHYSICAL PROPERTIES OF THEEASTERN TROPICAL NORTH PACIFIC WITH El-fPHASIS ONTHE OXYGEN MINIMUM LAYER

7. AUTHOR(e)

Louis A. Codispoti

9. PERFORMING ORGANIZATION NAME AND ADDRESS

University of WashingtonDepartment of OceanographySeattle, Washington 98195

I I. CONTROLLING OFFICE NAME AND ADDRESS

Office of Naval ResearchLa Jolla, California

14. MONITORING AGENCY NAME 6 ADDRESS(II dillerent lrom Controllln, Oillce)

5. TYPE OF REPORT 6 PERIOD COVERED

INTERIM 1959-1972I. PE"'ORMING ORG. IItEPORT NU!ABER

M73-64I. CONTRACT OR GRANT NUMSER(eJ

Contract Nonr-477(37) andN-00014-67-A-Ol03-00l4

10. PROGRAM ELEMENT. pqOJECT. TASf(AREA 6 WORK UNIT NUMBERS

Project NR 083 012

12. REPORT DATE

October 197313. NUMBEIit OF PAGES

38IS. SECURITY CLASS. (01 t.~'. report)

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Approved for public release: distribution unlimited

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II. SUPPLEMENTARY NOTES

19. KEY WORDS (Continue on rove,.o .Ide II nece..ary end Identify by block number)

Oceanographic data rnomas G. Thompson cruisesPhysical oceanographic data Other agencies cruisesChemical oceanographic data Eastern tropical North PacificOxygen minimum layer

20. ABSTRACT (Continuo on rovo,ee .Ide "nec••eary end Identify by bloclc number)This report is basically an atlas presenting diagrams and charts of

temperature, salinity, oxygen, nutriEnt, and relative baroclinic current datafor the eastern tropical North Pacific. Special emphasis is on the oxy~en

deficient layer in this region and a number of the charts constitute anisentropic study of this layer. Two of the included properties, nitratedeficits and equivalent nitrate, are particularly appropriate for investi~a­

tions dealing with denitrification in these waters, and the methods forcalculating them are described. '.. ...- . -

DO FORM1 JAN 73 1473 EDITION OF 1 NOV 65 IS D.SOLETE

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20. (Continued)A temperature-salinity, temperature-oxygen diagram presents evidence

for significant respiration at depths of about 800 m.

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