Oxygen Consumption in the Ocean: Measuring and Mapping with

10 Oxygen Consumption in the Ocean: Measuring and Mapping with Enzyme Analysis

Downloaded by TUFTS UNIV on October 23, 2016 | http://pubs.acs.org Publication Date: August 1, 1985 | doi: 10.1021/ba-1985-0209.ch010

T. T. PACKARD Bigelow Laboratory for Ocean Sciences, M c K o w n Point, West Boothbay Harbor, M E 04575

The chemical basis of oceanic oxygen consumption originates with enzymatic reactions in plankton. This chapter discusses the measurement of the reaction rate of the enzyme systems that control 90 % of the planktonic oxygen consumption. The reaction rate then gives the potential rate of oxygen consumption, from which oxygen consumption rates can be calculated in upwelled sewage, upwelling ecosystems, and abyssal waters. The use of an automated enzyme analyzer for mapping rates of oxygen consumption is also described. These maps show association between upwelled seawater and low oxygen consumption rates and between mature, seasoned upwelled seawater and high oxygen consumption rates. Deepwater oxygen consumption was associated with enhanced surface productivity and was used to calculate age and currents in the deep ocean. For waters 3000 m below the Peruvian Current, an age of 685 years and a current speed of 0.6 mm/s were calculated. MAPPING C R I T I C A L W A T E R Q U A L I T Y I N D I C E S I N R E A L T I M E is necessary for the development and verification of realistic mathematical models of the ocean. The advent of automated chemical analyses and computer mapping (1-4) has made real-time mapping of static chemical properties a reality. But these static properties, for example, nutrient salts, chlorophyll, and salinity, are not sufficient to describe the state of a system, nor can they be used to predict the recovery of a perturbed system. The dynamic properties, especially those that control the remineralization and oxidation of organic matter to C 0 and N 0 , namely oxygen consumption, denitrification, and nitrification, must be measured (5-8). These processes are 2

3

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Zirino; Mapping Strategies in Chemical Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1985.

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M A P P I N G STRATEGIES I N C H E M I C A L

OCEANOGRAPHY

normally measured by time-consuming incubation techniques that, although useful for experimental small-scale studies, are too slow to ensure the rapid information feedback required for mesoscale oceanographic studies. This chapter focuses on measuring and mapping the rate of oxygen consumption i n surface and deep ocean waters, examines the biochemical basis of oxygen consumption, and demonstrates how knowledge of this biochemistry can be used to calculate and map oxygen consumption in the sea.


The Chemical

Basis of Oxygen

Consumption

Oxygen consumption, i n contrast to oxygen production, occurs at all depths and regions of the ocean where oxygen and organisms are present. Without the organisms oxygen consumption would cease because nonenzymatic utilization of oxygen is negligible (9). Because marine microorganisms are ubiquitous, oxygen consumption always proceeds at some finite rate. This rate of consumption reflects their metabolism, which in turn reflects the oxygen consumption of many enzyme-catalyzed reactions. These reactions fall into two groups: those associated with oxidative phosphorylation—the production of adenosine triphosphate (ATP) (JO, 11)—and those associated with nonphosphorylating oxygenases i n the microsomes and cytoplasm (12, 13). In the first group are the reactions coupling the oxidation of organic matter by glycolysis: C H e

1 2

0

6

+ 2NAD + + 2 P 0 3

2CH COC0 3

2

+ 2ADP

2

+ 2 N A D H + 2H+ + 2 A T P + 2 H 0 2

(1)

and the tricarboxylic acid cycle: CH COC0 3

+ 2H 0 + F A D + 4NAD+-*

2

2

3C0

2

+ FADH

2

+ 4NADH + 4 H

+

(2)

with the oxidative phosphorylation of the electron-transport system (ETS): NADH + H

+ 5ADP + 5P0 ~-+ N A D + F A D + 2 H 0 + 5ATP (3) A reaction associated with nonphosphorylating oxygenases is shown in Reaction 4, an example of a minor oxygen-consuming reaction in biological systems. The oxygen consumption by cytochrome P-450 occurs in the microsomes of animals and the "mierobodies" of plants. +

+ FADH

2

+

+ 0

2

3

+

RH + 0

2

+

2

2

+ N A D P H + H - * R O H + H 0 + NADP+ +

2

(4)

where R represents substrates such as natural lipids and foreign lipophilic substances.



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Both groups of reactions are found i n bacteria (14), all higher animals (15), and plants (16); however, oxidative phosphorylation is responsible for 90 % of the oxygen consumed (17). Oxidative phosphorylation is driven by the respiratory electron-transport system that is embedded in the lipoprotein inner membrane of eukaryotic mitochondria and in the cell membrane of prokaryotes. It consists of four complexes (Scheme I). The first is composed of nicotinamide adenine dinucleotide ( N A D H ) oxidase, flavin mononucleotide ( F M N ) , and nonheme iron-sulfur proteins (18,19), and it transfers electrons from N A D H to ubiquinone. The second is composed of succinate dehydrogenase (SDH), flavin adenine dinucleotide ( F A D ) , and nonheme iron-sulfur proteins (20), and it transfers electrons from succinate to ubiquinone (21, 22). The third is composed of cytochromes b and c, and nonheme iron-sulfur proteins (23), and it transfers electrons from ubiquinone (UQ) to cytochrome c (24). The fourth complex consists of cytochrome c oxidase [ferrocytochrome c : 0 oxidoreductase; E C 1.9.3.1 (25)] which transfers electrons from cytochrome c to 0 (26, 27). 2

2

These four complexes together are often referred to as the respiratory chain, but their organization is better described as a multienzyme system than as a chain (28). Accordingly, these four complexes w i l l be called the electron-transport system (ETS) throughout this chapter. At the terminal end of the E T S , cytochrome oxidase is the ultimate mediator between intermediary metabolism and oxygen; however, its rate-limiting role has been preempted by the flavoprotein end of the E T S (17). Chance and W i l liams (29-31) demonstrated this preemption by calculating first-order rate constants for each step in the E T S . They showed that flavoprotein oxidation occurred at one-half the reaction rate of the cytochrome oxidase reaction. Therefore, the consumption of oxygen by mitochondria can only proceed as fast as the maximum velocity of the flavoenzymes, that is, the N A D H - u b i q u i n o n e ( E C 1.6.5.1) and the succinate-ubiquinone oxidoreductase ( E C 1.3.99.1). Oxygen Consumption: The Basis of Energy Production The purpose of oxidative phosphorylation is to generate A T P . Because all living systems are in a nonequilibrium state, they require this energy to maintain themselves against the constant tendency to degrade and deteriorate according to the second law of thermodynamics. Furthermore, if these living systems are to grow, reproduce, or pursue an aggressive existence they require additional energy. Therefore, they first developed the substrate-level phosphorylation reactions, such as those i n glycolysis, and second, they developed phosphorylating membranes that utilize the free energy of succinate and N A D H oxidation to produce A T P . The oxidation is carried out by the four complexes of the E T S embedded i n these membranes. Thus, oxygen consumption and A T P production are coupled. The four electron-transport complexes generate and maintain a proton differential (ApH) and an electric-charge differential (an electromotive force



H

k

E T S according to Chance ,(1977)

UQ-Cytb -b

(Fe-S)s-2

f

m Cyt c , ( F e - S ) C y t c

3

Cu-Cu

Cyt a - o

t

Abbreviations: FAD, flavin adenine dinucleotide; Fe-S, iron-sulfur proteins that can be identified in separate clusters by electron paramagnetic resonance analysis (the s-1, s-2 subscripts identify these iron-sulfur proteins as part of the succinate dehydrogenase complex); His, the histidine linkage between FAD and the large (70,000 daltons) protein moiety of the enzyme; FMN, flavin mononucleotide; N-la, N-2 subscripts identify these iron-sulfur proteins as part of the NADH-dehydrogenase complex; UQ, ubiquinone; Cyt b and Cyt by cytochrome b-566 and b-563, respectively.

Scheme I. The electron flow pattern between the electron donors (succinate and NADH) and the electron acceptor (oxygen) in the mitochondrial respiratory ETS. The diagram shows the organization of the ETS into four isolatable enzyme complexes.

NADH-

His

I

FAD ( F e - S ) s - i ( F e - S ) s - 3

(Fe-S)N-ib (Fe-S)N-s F MN (Fe-S) N-ia-(Fe-S>N-4-(Fe-S)Va (Fe-S)N-s

Succinate -


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181

symbolized as A ^ ) across the mitochondrial inner membrane or across the bacterial plasmalemma. The sum of the p H and charge differentials produces the protonmotive force (P), which is the source of energy for mitochondrial A T P synthesis: P = A * - 2.3[HT(ApH/F)]. The synthesis is actually carried out by the enzyme, A T P synthase, that discharges the proton differential and simultaneously phosphorylates A D P (15, 17, 32, 33).


Topology of the Complexes in the Mitochondrial Membranes The subunits of the respiratory electron-transport system can be isolated and studied independently of each other. Hackenbrock (28) presented data supporting the argument that these complexes (see Scheme I, 34) are not arranged i n linear sequence as i n a chain, but are randomly distributed in the "plane" of the inner membrane. They are oriented with their long axis perpendicular to the plane of the membrane with 70-83% of their mass extending into cytosol and matrix space on either side of the membrane. Furthermore, Hackenbrock argues that they can migrate independently in the membrane plane i n response to electrophoretic forces. This conceptual model of the electron-transfer complexes migrating randomly i n the plane of the inner membrane has been modified by C a paldi (35), who argues that the high-protein concentration (50%) in the mitochondrial matrix (36) would retard the lateral migration. In his modification, the electron-transfer complexes, as well as the A T P synthetase and the A T P - A D P translocase complexes, are fixed in the membrane rather than being free to migrate laterally (Figure 1). This change does not impair the capacity to transfer electrons because ubiquinone is left free to diffuse randomly and transfer electrons from Complexes 1 and 2 to Complex 3, and cytochrome c is left free to transfer electrons from Complex 3 to C o m plex 4 (Figure 1). Capaldi (35) calculates that cytochrome c can collide with both Complexes 3 and 4 within a single turnover time of the E T S (50100 ms/cytochrome c oxidase). Bacterial Oxygen Consumption In bacteria, oxygen consumption associated with oxidative phosphorylation occurs i n the cell membrane because these organisms do not have m i tochondria (37, 38). In this membrane the E T S is organized similarly to the E T S i n eukaryotes (39), that is, it has the same basic iron-sulfur proteins, flavoproteins, quinones, and cytochromes to transfer electrons from the dehydrogenases to oxygen. However, some differences exist, the most striking of which occur at the terminal oxidase. The cytochrome c oxidase of mitochondria is often supplemented w i t h simpler polypeptides i n the form of cytochrome o (26), or cytochromes d , z j , and c (39, 40). Other differences are (1) the ubiquinone (coenzyme Q) of mitochondria is often supplemented or replaced by an analog, menaquinone; (2) cytochrome c is sometimes missing; (3) transhydrogenases at the dehydrogenase level are comco


182

OCEANOGRAPHY



Figure 1. Distribution

of the electron-transport complexes in the inner membrane.

mitochondrial

The upper diagram is a planar view; the lower one is a cross section through the membrane. Each complex has been drawn to scale according to Capaldi (35); the distance between Complex 1 and 3 is approximately 310 A and between Complex 3 and 4, it is approximately 255 A. The area around Complex 3 in the upper panel is about 200,000 A. (Reproduced with permission from Ref. 35.)


10.

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183

mon; and (4) the E T S often branches after the quinone level to accommodate two terminal oxidases (39, 40). Regardless of these differences, the respiratory capacity, and the molecular properties of the terminal oxidases, the bacterial E T S is not significantly changed.


Oxygen Consumption in Plants Four types of oxygen consumption occur i n plants; dark respiration, photorespiration, chloroplast respiration, and cyanide-resistant respiration. Other reviews of photorespiration have been published (41, 42); therefore it w i l l not be discussed here. Also, because knowledge of respiratory E T S i n plants is based on the higher plants in contrast to the algae, this section w i l l be confined largely to the higher plant literature. Chloroplast respiration is a novel form of respiration that has only recently been discovered. Chloroplast membranes exhibit a nonphosphorylation E T S that consumes oxygen (48). Ferredoxin and reduced nicotinamide adenine dinucleotide phosphate ( N A D P H ) serve as electron carriers and glyceraldehyde-3-phosphate serves as the electron donor. This system probably originated i n the respiratory E T S of the ehloroplast's free-living ancestors, the cyanobacteria (49). The most important form of plant respiration is housed i n the mitochondrial inner membrane just as it is i n mammals, and the system is similarly composed of N A D H and succinate dehydrogenase, ubiquinone, and cytochromes b, c, c a, and a . However, plant mitochondria have additional pathways to oxidize exogenous N A D H , N A D P H , malate, and other substrates as well as an alternative, cyanide-resistant, redox link between ubiquinone and oxygen (Figure 2). These pathways provide plants with a variety of responses to meet changes i n metabolic and environmental conditions. Both the outer and inner mitochondrial membranes of plants contain N A D H dehydrogenases, which give plant mitochondria the ability to oxidize exogenous N A D H and sets them apart from mammalian mitochondria that normally only oxidize exogenous succinate (43). Plant mitochondria also have the ability to oxidize exogenous N A D P H without transhydrogenation to N A D H . Oxidation is done via a rotenoneresistant pathway that bypasses Site I (Figure 2) and transfers electrons to ubiquinone (44-45). A third characteristic of plant mitochondria is the presence of an alternative oxidase that enables plants to consume oxygen in the presence of cyanide and other inhibitors of cytochrome oxidase (Figure 2). The physiological purpose of this alternative oxidase and its chemical pathways are unknown. It could serve as a heat-generating mechanism analogous to brown adipose tissue in mammals (46), or it could serve to oxidize potentially harmful fatty acid peroxy radicals (47). Enough research has not been done to strongly support either mechanism. l9

3


184


OCEANOGRAPHY

Glycolysis NADH (Cytosolic)

cytoplasm

N A D H Dehydrogenase

Cytc

Inner Mitochondrial Membrane


[Cytb-Cytc] complex Site I Succinate dehydrogenase

Alternative oxidase

NADH (Mitochondrial)

Oo

HoO

cyt a

3

OgHaO MATRIX

* TCA

Cycle •

Figure 2. The respiratory ETS in plant mitochondria and the position of "alternate oxidase." (Reproduced with permission from Ref. 43.)

the

Minor Oxygen-Consuming Systems Although the oxygen consumed during oxi(' itive phosphorylation accounts for 90 % of the oxygen utilization of living organisms (at least for all the higher organisms, yeast, protozoans, and bacteria studied so far), many other enzymes require oxygen. Furthermore, nonphosphorylating electron-transport systems are found i n the endoplasmic reticulum of higher organisms and i n some bacteria. One E T S degrades fatty acids and uses N A D H as the electron donor while transporting electrons via cytochrome b to oxygen (13). A second E T S (Reaction 4) degrades steroid hormones and xenobiotics via N A D P H , flavoproteins, and cytochrome P-450 (50). It also uses oxygen as the ultimate electron acceptor; the rate-limiting step occurs before the terminal oxygenase. In addition, other oxidases and oxygenases not associated w i t h membrane preparations degrade a variety of amino acids and phenolic and other compounds. Ascorbate oxidase, tryptophan 5-monooxygenase, and lactate monooxygenase are examples (51). 5


10.

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However, because these systems play a minor role i n the economics of oxygen consumption in living systems, they w i l l not be discussed further.


Methods In the research reported here we have assessed the oxygen-consumption rate at the sea surface, i n the deep sea, and i n vertical ocean profiles by employing the biochemistry of oxygen consumption. To a first approximation this biochemistry is nearly identical i n bacteria, protists, metazoans, and plants (15-17, 39). Accordingly, we assume that this universalism extends to phytoplankton, zooplankton, and bacterioplankton, and we reasoned that by measuring the rate-limiting reaction of the oxygen consumption process i n oceanic microbes we could calculate their oxygen consumption rate. Therefore, we used an enzyme assay that measures the combined activities of succinate-tetrazolium oxidoreductase ( E C 1.3.99.1), N A D H - t e t r a z o l i u m oxidoreductase ( E C 1.6.99.3), and N A D P H - t e t r a z o l i u m oxidoreductase ( E C 1.6.99.1) i n samples of oceanic particulate matter (52-61). The tetrazolium that we used is 2-(piodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT). Reaction 5 shows the potential sites of I N T reduction i n beef heart mitochondria (62, 64). NADH—-^^1 INT CCoO 1 INT ^ . s u c c i n a t e ^ P " ^ [ c y t bj — ^

_~

,

,

F

a

_~ ^ °

a

/ K X 2

() 5

Reaction 6 shows the range of sites over which I N T is reduced by the E T S i n artichoke mitochondria (63, 64). succinate-+Fp->CoQ-»Cyt b~»Cyt c->Cyt a a - > 0 3

INT"

2

(6)

*formazan

The enzyme activities measured by this assay represent the maximum reaction rate (V) of succinate dehydrogenase ( E C 1.3.99.1) and N A D H ubiquinone oxidoreductase ( E C 1.6.99.3)(see Scheme I, Complexes I and II), which are the electron-donor systems to the cytochrome chain (Complexes III and I V ) . Because the electron-donor systems are rate limiting, the assay measures the capacity ( F ) of the respiratory E T S . In addition, the N A D P H - t e t r a z o l i u m oxidoreductase provides an estimate of the oxygen-consuming capacity of the microsomal E T S (Reaction 4) (64). The E T S assay was developed to rapidly assess the oxygen consumption rate i n both the deep sea and i n the surface waters (52-58). As developed, the assay measures the combined oxygen-consuming capacity of living microbial populations. By using the assay, the depth profiles of the i n situ oxygen consumption, or as C r a i g (86) calls it, "the deep-metabolism," can be dem a x



186


OCEANOGRAPHY

termined within hours to many thousands of meters. W h e n automated and interfaced with a data-acquisition and computer-mapping system, the E T S assay can be used i n surface water to provide maps of oxygen consumption within hours after an ocean survey is completed (65). This chapter describes the use of this enzyme assay i n investigations of upwelling off Oregon, Peru, and Mauritanea, i n a survey of a sewage outfall off Los Angeles; and i n an open ocean survey of the Costa Rica Dome. Only i n the upwelling survey off Mauritanea was the automated version of the assay used (65). The manual methods were used for the deep water below the Costa Rica Dome (58), for the near-surface waters of the outfall off Los Angeles, and for the Oregon upwelling (56). These manual methods have been discussed elsewhere (66-68). The Automated E T S Assay. The automated E T S assay system was a laboratory-built (51), enzyme-analysis system dedicated to measurements of the respiratory E T S i n cell-free homogenates (Figure 3). The system facilitated the processing of the large number of seawater samples that are required to map seawater oxygen consumption during ocean survey cruises. It ensured standardization of the timing and performance of all the manipulations and transfers i n the chemical phase of the enzyme assay. This automated system has been used to map seawater oxygen consumption rates i n the euphotic zones of upwelling and coastal waters (51); it has not been used to map the rates i n oligotrophic or deep-sea waters. The system was designed for computer interface i n a manner similar to the nutrient Autoanalyzer array. It had a potentiometric output, 0-1 linear w i t h 0-1 absorbance from the spectrophotometer. The starting switch flagged a data-acquisition system that took readings every 15 s for 3.5 m i n . The enzyme reaction was zero order and linear with time during the incubation period. Reaction rates were calculated by regression analysis of the time course. The device did not free the analyst of all hand manipulations. The cell-free homogenate was prepared by hand and injected into the mixing chamber; then the system proceeded automatically. A l l reagents were prepared according to Kenner and Ahmed (59). Fifteen seconds after starting, a pair of syringe pumps added the reagent mixtures (Figure 3). The reagents were preheated, mixed for 15 s i n the mixing chamber with the homogenate, and then drawn into the temperaturecontrolled reaction chamber and flow cell where the mixture was monitored. Later the excess was removed, and the mixing chamber and flow cell were rinsed with distilled water. A l l of the subsystems returned to their base state quickly and were ready for immediate use. A complete cycle took 5 m i n ; this rate enabled the apparatus to make 12 analyses per hour, a rate comparable to data-acquisition rate for seawater nutrient analysis. The rate of reduction of I N T to the insoluble formazan (64) (Reaction 7) i n the flow cell was measured by the absorption of the reaction mixture at 490 n m (59). A blank was prepared identically except that homogeniza-


PACKARD

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187


10.

Figure 3. The electron-transport system. Reactants are pumped from storage, then heated and injected into a mixing chamber (black flow lines). Sample is added to the mixing chamber, the mixture is injected into the flow cell, and the formazan production is monitored every 15 s for 3.5 min. The mixture is flushed, the system is rinsed, and the cycle begins again. The hatched regions are maintained at surface seawater temperatures. The four solenoid valves function most of the time in normally open (NO) or normally closed (NC) positions. A Technicon Autoanalyzer pump and a Bausch and homo Spectronic 88 spectrophotometer were used.


188


N


c r

+

II N

+ 2 H + 2e~

HC1 +

+

INT

OCEANOGRAPHY

N

N || N

(7)

NH

Formazan

tion buffer was substituted for homogenate i n the reaction mixture. The average of several blanks was subtracted from the assay to obtain the rate of the enzymatically catalyzed tetrazolium reduction. The calculation of E T S activity accounts for the liters of seawater sampled (v) and the m i l l i l i ters of the homogenate used (/), and the milliliters of the reaction mixture (S) (59). The following equation was used for calculating E T S activity (milliequivalents per hour per liter): ETS = [7.54 SH (A - B)]/fv, where H is the volume of the uncentrifuged homogenate in milliliters, A is the change in absorbance of the 10-mm light path per minute, and B is the absorbance change i n the blank. The units of [SH (A - B)]lfv are absorbance per mole per liter. The coefficient, 7.54, incorporates the molar extinction coefficient of the I N T formazan (Al % = 15.9 X 10 /M cm), the two-electron stoichiometry of I N T reduction (Reaction 7), and a time conversion. Because the E T S activity (ETS ) is measured at a constant temperature (T ) and the samples were drawn from seawater of varying temperature (T^), a temperature correction must be made to calculate the E T S at i n situ temperature (ETS;). W e used the following expressions based on the Arrhenius equation: 0

9

m

3

0

Q

0

where R is the gas constant (1.987 cal/mol deg), and 15.8 is the activation energy in kilocalories per mole (57). Both the incubation (T ) and in situ (T|) temperatures were expressed i n absolute temperatures. Interpretation of the E T S Measurement: Conversion of Oxygen C o n sumption. The measurement of E T S activity i n oceanic particulate mat0


10.

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in the Ocean

ter is a measure of the capacity or potential of that matter to consume oxygen. It is not a measurement of the i n situ rate. The relationship between the i n situ rate (r) and the potential rate (R) may be controlled either by the A D P concentration (29-31, 69), by the ratio of A T P to A D P (70-72), or by the ratio of A T P to A D P and inorganic phosphate (Pj) (73) by an expression analogous to the Michaelis-Menten expression, r = SR/(K + S), where S equals either [ A D P ] , [ADP]/[ATP], or [ADP]/([ATP] X [PJ), and K equals the level of S at which r = 1/2B. However, because the respiratory control is not well understood (69-74), an average value for SI(K + S) has been determined experimentally i n cultures and i n the field and is used to calculate i n situ oxygen-consumption rates from E T S measurements (60, 61, 75, 76). A detailed discussion of these coefficients is found elsewhere (66-75); a brief discussion follows. For phytoplankton and phytoplankton-dominated euphotic zones, a coefficient of 0.15 is used with the Kenner and Ahmed (59) version of the E T S assay. This coefficient is the average ratio of respiration to E T S activity i n eight species of phytoplankton, mostly diatoms (Table 1). In calculating this average, the results for Ditylum brightwellii were excluded because they appeared to be anomalous. The ratio was determined on organisms in their log growth phase, and no dinoflagellates were used i n the experiments. Thus, although this ratio has been used i n assessing respiration from E T S measurements i n many euphotic zones (54), it should be most accurate in diatom blooms. A t the end of a diatom bloom, when the inorganic nutriM

M


M

Table I. Ratios of Oxygen Consumption In Vivo to Respiratory Electron-Transport Activity In Vitro in Marine Phytoplankton Phytoplankton Bacillariophyceae (Diatoms) Coscinodiscus angstii Cyclotella sp. Ditylum brightwellii Phaeodactylum tricornutum Skeletonema costatum Thalassiosira fluviatilis Chlorophyceae Dunaliella tertiolecta Coccolithophorids Cricosphaera carteri Haptophyceae (Isochrysids) Isochrysis sp.

Respiration/ETS

N

0.137 0.106 0.319 0.161 0.151 0.135

± 0.006 ± 0.006 ± 0.010 ± 0.007 ± 0.008 ± 0.011

17 10 13 10 11 8

0.169

± 0.016

12

0.159

± 0.007

11

0.177

± 0.018

14

N O T E : E T S activity was converted to oxygen equivalent units (5,6 L of oxygen is reduced by 1 electron equivalent) so the respiration-ETS ratio is unitless. The number of experiments is given by N. D a t a are taken from Reference 6 0 .



190

MAPPING STRATEGIES IN CHEMICAL OCEANOGRAPHY

ent salts have been stripped from the seawater, a lower ratio should be used. Ratios as low as 0.06 have been found (60) for such nutrient-deficient conditions i n culture. In working with bacteria or zones i n the ocean where bacteria dominate the biological community, a different coefficient should be used. In situations where the bacteria are growing and the E T S method of Packard et al. (55) is used to determine the oxygen consumption, a coefficient of 5.0 should be used. This value is based on 49 experiments with five species of marine bacteria (76). In situations where the bacteria are not growing, as in senescence, a coefficient of 0.43 should be used (Table II) (76). Calculations of deep-sea oxygen-consumption rates (68, 76) were made with the assumption that the deep water populations were dominated by bacteria i n a senescent phase; therefore, the coefficient of 0.43 was used.

Table II. The Ratio of Respiratory Oxygen Consumption to ETS Activity in Five Species of Marine Bacteria in Three Different Stages of Batch Culture Mean

Coefficient of Variation (%)

N

growth senescent

2.91 0.492

12 9

6 24

growth senescent growth senescent starvation

4.40 0.468 5.90 0.434 0.110

7 6 41 25 28

6 6 7 4 4

growth senescent

5.63 0.445

19 14

6 18

growth senescent

8.25 0.491

26 19

6 18

growth senescent growth growth senescent senescent

4.78 0.306 3.84 5.02 0.426 0.110

35 38 20 29 20 28

9 28 9 49 98 4

Phase

Species Vibrio adapiatus Peptone Vibrio anguillarumP Peptone Glucose Vibrio sp. SA774 Serratia marinorubra Peptone Pseudomonas perfectomarinus Peptone 1 and Peptone 2 Glucose Weighted mean

a

"Growth-phase data represent means of all samples prior to attainment of maximum populations; senescent-phase data represent means of samples taken following termination of growth i n w h i c h stable, steady cellular levels of respiration and E T S had been attained; and the starvation data indicate the further depression of respiration-ETS following senescence. ^Following glucose depletion, V. anguillarum never attained steady levels of respiration per cell. T h e respiration-ETS of senescent P. perfectomarinus from experiments Peptone 1 and Peptone 2 were not significantly different (P < 0.10) and were pooled. c


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Direct determinations of oxygen consumption i n surface seawater have become possible (77) so that E T S measurements can be directly calibrated under field conditions (Figure 4) (67). For research i n the upper 50 m of the ocean, direct calibration w i l l become the preferred procedure.


Observations and Results Oxygen Consumption i n Near-Surface Waters of Coastal Upwelling Areas. Oxygen consumption i n the surface waters of the California Bight off Los Angeles, the Oregon upwelling off Cascade Head, and the northwest African upwelling off Cape Blanc was mapped by measuring E T S activity. The maps show that oxygen consumption i n the surface water cannot be treated as a constant i n either the time or space domain. C A L I F O R N I A B I G H T . This experiment was designed to test the prediction that the effluent from a sewage outfall i n an upwelling area would significantly enhance the respiratory oxygen-consumption rate i n the surface waters by stimulating either a phytoplankton or a bacterioplankton bloom. In this test, the rate of oxygen consumption, chlorophyll, nutrient salts ( P 0 " , N 0 " , N H , and silicate), temperature, and salinity off Los Angeles i n the vicinity of L o n g Point and Whites Point (Figure 5) were mapped. Upwelling occurred off L o n g Point, and industrial waste was discharged off Whites Point. The outfall discharged ammonium, phenols, and other noxious wastes into the ocean at the 50-m level through a diffuser designed to dilute the sewage so that it would not penetrate the thermocline and rise to the surface. If the system had worked according to design, the ammonium-rich effluent would not have risen into the euphotic zone; however, the natural upwelling i n the region defeated the design. The currents at 25 m traveled northwest, the surface currents traveled southeast, and upwelling occurred near L o n g Point (78, 79). So, the sewage flowed at depth toward L o n g Point, was upwelled, and then moved back toward Whites Point i n the surface flow (Figure 5). Because the sewage, when properly diluted, w i l l set up a plankton bloom, high oxygen-consumption rates, and high algal or bacterial biomass off L o n g Point were expected. O n all three dates of the mapping survey (March 31, A p r i l 1, and A p r i l 4) the highest levels of oxygen consumption and phytoplankton biomass lay i n shore along the coast between L o n g Point and Whites Point. O n A p r i l 4, a distinct plume was evident i n both the oxygen-consumption rate and phytoplankton biomass (Figure 5). This plume occurred following a period of upwelling i n which ammonium and nitrate rose into the euphotic zone (Figure 6). O n A p r i l 2, A p r i l 3, and again late on A p r i l 4, high ammonium (> 4 ptM) levels could be found at 10 m i n the inshore region of the survey (Figure 6). This ammonium enrichment could easily have stimulated plankton growth that led to the development of the blooms on A p r i l 4 (Figure 5C). Therefore, the plume structure i n the oxygen-consumption rate 4

3

3

4

+




192

Figure 4. Two examples of the relationship between ETS activity and the oxygen-consumption rate in natural seawater samples (top) and in laboratory cultures of the marine bacterium, Pseudomonas perfectomarirms (bottom). Top: the equation R = 1,92 ETS - 0.99, where R is the oxygen-consumption rate, describes the samples taken from the Georges Bank-Gulf of Maine cruise on the R. V. Eastw a r d in July 1980. Bottom: the equation R = 1.29 ETS + 4.71 describes the ETS dependence of oxygen consumption of the bacterium, P . perfectomarinus. The differences in the equations may reflect the differences of the analysis of bacterial and phytoplankton ETS. In bacteria the ETS is housed in the cell wall, so crude homogenates must be used. In phytoplankton the ETS is housed in the mitochondria; thus, partially purified homogenates free of cell walls and nuclei are used. (Reproduced with permission from Ref. 67 and 75.)



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Figure 5. Oxygen consumption (left) and chlorophyll (right) in the surface waters (3 m) on three different dates off the Polos Verdes district of Los Angeles. The three maps were made on March 31(A), April 1(B) and April 4(C) during the Outfall I cruise of the R. V. Thomas G . Thompson. The ranges of nutrient ana temperature conditions are summarized in Figure 6. Note the well developed plume on April 4. Oxygen consumption was calculated from ETS activity measurements. A manual version of the ETS assay (53) was used.

was probably caused by a phytoplankton bloom that, i n turn, was fed by ammonium upwelling at L o n g Point (Figure 7) that originated at the Whites Point sewage outfall. Whitledge et al. (78) came to a similar conclusion on the basis of hydrographic data. O R E G O N C O A S T . U p w e l l i n g occurs along the Oregon coast every summer (Figure 8). C o l d waters with temperatures as low as 6 °C up well


194

MAPPING

STATION

m

STRATEGIES

STATION

N

IN CHEMICAL

OCEANOGRAPHY

2

4 ?

(/JM)


A M M O N I U M

(;JM)

A M M O N I U M

B 10-

20

w

30

UJ

4 0

5

50

x NITRATE

Q

NITRATE(pM)

(juM)

70

TEMPERATURE

29

30

31

29

MARCH

30 MARCH

T I M E

(days)

31

I

2

(°C)

3 APRIL

T I M E ( days)

Figure 6. Time-series depth profiles of ammonium, nitrate, and temperature in the inshore region (Stations 47, 55, 58, 62, 69, and 70) and the offshore region (Stations 48, 56, 59, 67, and 71) between Long Point and Whites Point off Los Angeles. Note the ammonium-rich subsurface waters rising between March 31 and April 3, and also the rising isotherms over the same period in the inshore stations. Warm nutrient-poor surface waters after April 3 suggest an incursion of offshore water. (The station locations can be found in Figure 1 of Reference 79.)


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Oxygen Consumption in the Ocean STATIONS


58 (INSHORE)

59

(OFFSHORE) 6 0

Ammonium Section off Long Point ( / J M )

60 Figure 7. The rising isopleths of seawater ammonium along an section at Long Point, Los Angeles.

offshore-onshore

The ammonium serves as a tracer for the effluent from the White Point sewage outfall. Its rise to the surface at the inshore station is driven by coastal upwelling. Once the ammonium breaks into the euphotic zone it can stimulate phytoplankton growth.

to the surface and bring w i t h them nitrate levels as high as 28 pM. A plankton bloom should be stimulated by this nutrient injection, and this bloom should stimulate the total plankton community to consume more oxygen. Thus, the rate of oxygen consumption should increase offshore as the plankton population increases. T o test this prediction, the oxygenconsumption rate, temperature, salinity, nitrate, ammonium, nitrite, and chlorophyll were mapped i n the upwelling region. O n the first three passes cold water up welled next to the coast, especially off Cascade Head. Nitrate levels decreased from 24-28 pM inshore to undetectable levels offshore (80). The chlorophyll and the oxygen-consumption rate displayed an i n verse trend w i t h respect to nitrate and temperature. Oxygen-consumption rates and chlorophyll were low inshore and high offshore (Figure 8). O n the last survey the system had relaxed and the w a r m offshore water had moved i n over the area like a blanket. The lowest temperature i n the area was 14.6 °C where previously water of 8 °C could be found, and the rate of oxygen consumption, which previously had increased offshore, now decreased from 8 ph of 0 / h L inshore to less than 2 pJL of 0 / h L offshore (Figure 9). Thus, two contrasting patterns of oxygen consumption i n an 2

2




196

Figure 8. The offshore temperature gradient and offshore oxygen-consumption gradient along the Oregon coast when upwelling is strong ( C U E II expedition). The highest rates of oxygen consumption occur offshore. These measurements and those in Figures 7 and 9 were made with the manual ETS assay.



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Figure 9. The offshore temperature (left) and oxygen-consumption (right) gradients along the Oregon coast when the upwelling relaxes ( C U E II expedition). The highest rates of oxygen consumption occur inshore.

upwelling system emerged. The pattern for an upwelling event is low oxygen consumption in the freshly up welled inshore water, increasing to high oxygen consumption offshore where the nutrient-rich water has stabilized in the surface waters and produced a plankton bloom. The pattern for an upwelling reversal or relaxation event is high oxygen consumption i n the warm inshore water that has recently flowed onshore to replace the subsiding upwelling source water. The stable, plankton-rich offshore water moves inshore along the coast and oligotrophic oceanic water stands just offshore. This plankton-poor water is characterized by a low oxygen consumption rate. NORTHWEST AFRICAN COAST.

The signature of a relaxation event was

seen i n the data from the Joint I expedition to the Mauritanean upwelling system i n M a r c h and A p r i l 1974. During the mapping study off Cape Blanc (Figure 10), winds were conducive to upwelling until A p r i l 7 (81, 82). Shortly after that date the temperature began to rise inshore (81) and by A p r i l 9 the system had relaxed. As off Oregon, the relaxation off Cape Blanc could be seen in the maps of the oxygen-consumption rates because the highest values are found inshore (April 9 and 10, Figure 10), where as during the upwelling they occurred farther offshore. The scenario of the upwelling that corresponds to maps of oxygen consumption in Figure 10 is described elsewhere (82). The upwelling along the coast was strong for the week preceding G r i d 17 (Figure 10, March 3 0 A p r i l 5). D u r i n g this upwelling event the density throughout the water column increased, the offshore near-surface transport increased, and the



Figure 10. The sampling grid (left) and the resulting maps of oxygen consumption (right) in the northwest African upwelling system off Cape Blanc. These measurements were made with the automated ETS assay (Figure 3). The oxygen-consumption values are reported as percent of maximum on the right. The maximum values for the five grids were, from top to bottom, 1.25, 2.68, 3.21, 8.04, and 5.36 peq/Lh.



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temperature m i n i m u m and the nitrate and chlorophyll maxima moved to the edge of the continental shelf. The cross-shelf oxygen-consumption pattern that reflects the effect of this upwelling event on the metabolism of the plankton communities is shown i n Grids 17 and 18 (Figure 10). The oxygen consumption peaks at the outer shelf and proceeds at slower rates inshore and seaward of this maximum as expected from the results of the Oregon experiment (Figures 8 and 9). A t the end of the upwelling event the winds relaxed and then reversed (April 7-9). The cold nutrient-rich inshore water responded by subsiding, and the w a r m offshore water responded by moving i n close to the coast (81-83). The pattern of oxygen consumption on A p r i l 9 and 10 reflects this relaxation (Grids 19 and 20). The zones with the higher rate of oxygen consumption were found inshore of their previous positions i n Grids 17 and 18. The chlorophyll and photosynthesis maxima were likewise shifted inshore (81, 83). Between A p r i l 10 and 15 the winds blew toward the equator (upwelling favorable), and offshore transport resumed as during the M a r c h 3 0 - A p r i l 5 period. These events caused coastal upwelling to reoccur and pushed the zone of high-oxygen-consumption rate offshore (Grid 23) near its shelf-edge location as before (Grids 17 and 18). Thus, the zone of enhanced oxygen consumption responded to upwelling off northwest Africa as it responded to upwelling off Oregon. This zone is found offshore between the upwelling source water and the oceanic oligotrophic water during an upwelling event; it is found inshore i n front of the advancing oligotrophic water during a relaxation event. Oxygen Consumption i n the Deep Sea. The rates of oxygen consumption i n the deep sea are extremely l o w ; 1 uh/L per year below 300 m is a value obtained by many approaches (84-87). Nevertheless, as advectiondiffusion models show (85, 86), the oxygen consumption has a significant effect on the distribution of 0 , C 0 , C a C 0 , as well as N 0 ~, P 0 " , and silicate i n the deep sea (84, 85). Before 1971 deep-sea oxygen utilization was calculated from advection-diffusion (87, 88) or nutrient regeneration (85, 86) models. N o w calculations are based on microbial biomass (84, 89), E T S activity (55, 57, 58, 68), i n situ incubations with C - l a b e l e d substrates (90, 91), helium-tritium dating (92), or particle flux through the water column (93). F r o m the models, from biomass, from E T S activities, from dating techniques, and from particle-flux measurements, the oxygenconsumption rates, between 1 and 4 k m , fall i n the 0.1-40 ph of 0 / L per year range. F r o m the i n situ incubations, the rates appear to be much higher as has been shown with biological oxygen demand (BOD)-type measurements (94-96). Rates ranging from 5 to 77 ph of 0 / L per year were found (90, 91) but such rates are likely to drive the deep-sea anoxic (84). 2

2

3

3

4

3

14

2

2

VERTICAL DISTRIBUTION.

T h e deep-sea oxygen consumption rates

calculated from E T S activity fall i n the 0.05-6 pL of 0 / L per year range for the waters below 1 k m i n the Peru Current and Costa Rica Dome region. F r o m the sea surface to the bottom, the values diminish exponentially 2


200


with depth (68, 87, 93). A n empirical model was developed (93) for predicting deep-sea rates of oxygen utilization from particle-settling velocities and productivity i n the euphotic zone. F r o m this model, a family of depth profiles was predicted for oxygen utilization i n the water column (Figure 11). The ETS-derived values of oxygen utilization from the eastern tropical Pacific fall around the predicted profile for a surface productivity of 100 g of C / m per year. Estimates of productivity for the waters where the E T S measurements were made bracket this productivity value. Owen and Zeitschel (97) measured 70 g of C / m per year, and Broenkow (98) calculated 140 g of C / m per year. In agreement w i t h this model (93), Ben-Yaakov (99), Kroopnick (100), and Jenkins (92) showed that oxygen-utilization rates decrease exponentially. F o r the Peru Current and the Costa Rica Dome regions, Packard et al (68) found an exponential decrease of the form: JR = Kz~ . In the Peru Current the coefficient K and the exponent a were 1.15 and 1.0, respectively, and for the Costa Rica Dome they were 1.63 and 0.84, respectively. 2

2


2

a

HORIZONTAL DISTRIBUTION.

As the profiles just discussed show (93),

the deep-sea oxygen consumption rate should vary according to the surface productivity. T o demonstrate this covariation i n the Costa Rica Dome region, E T S activity was measured i n the deep sea, and chlorophyll and phytoplankton productivity were measured i n the surface waters during the PINTA expedition (58, 101). The results showed that under the statistical center of the Costa Rica Dome (9° N , 89° W ) (84) the deep-sea oxygen-

OXYGEN CONSUMPTION (ja I 0 liter" yr" ) 1

1

2

0

10

30

Figure 11. Depth profiles of oxygen consumption. The profile defined by the solid circles (•) was calculated from ETS activity measurements (o) as reported previously (55). The profile defined by the open triangles (A) is based on bacteriological studies (84). The family of continuous profile lines between A and B was generated by Sucss's (93) model of oxygen-consumption rates.


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consumption rate is fivefold higher than comparable rates 160 k m to the west (Figure 12). Therefore, surface water biological productivity has an observable effect on deep-water oxygen-consumption rates.


Discussion Sea surface maps of static properties such as temperature, chlorophyll a, nutrient salts, and p H are readily available to oceanographic research (I). They can be constructed with data from ships (102, 103), airplanes (J04), or satellites (105). Rarely, however, are sea surface maps constructed w i t h the dynamic properties such as reaction rates, growth rates, or current velocities because their measurement is intrinsically slow and technologically difficult. The time scales for measuring most of the dynamic processes relevant to chemical oceanography range from hours to days; consequently, by conventional methods, real-time mapping is not feasible. However, by employing enzyme analysis, the potential or the capacity of many rate processes can be mapped i n real time. The in situ rate can then be calculated from the potential rate and an empirically derived coefficient (66, 67), or from the potential rate and the kinetic control mechanism as described i n the "Methods" section. M a n y chemical reactions in the ocean could be mapped by this procedure. The rate of C 0 fixation could be mapped by measuring the activity of one of the enzymes associated with photosynthesis. Initial investigations with ribulose-l,5-bisphosphate carboxylase ( E C 4.1.1.39) have not been fruitful (106), but other photosynthetic enzymes have not been tried. As an example, the enzyme, ferredoxin-NADP-reductase ( E C 1.18.1.2), is theoretically a good candidate, because it serves as a major transmitter of reducing equivalents from the photosynthetic electron-transport system to a coenzyme ( N A D P ) commonly involved i n photosynthetic reactions. The rate of nitrate uptake and ammonium uptake could be mapped by measuring the activity of one or more of the enzymes associated with nitrogen assimilation. Nitrate reductase ( E C 1.6.6.1) is a good index of recent nitrate-reducing activity (107), and glutamine synthetase ( E C 6.3.1.2) may be a good index of ammonium uptake. A m m o n i u m production can be predicted from glutamate dehydrogenase ( E C 1.4.1.2) activity in zooplankton (108,109). This chapter has described some investigations into the use of the enzymatic activity of the respiratory E T S i n mapping the rate of oxygen consumption. The procedure was tried i n the surface waters of upwelling areas off Oregon and Mauritanea, i n the vicinity of a sewage outfall off Los Angeles, and i n the deep water (3000 m) below the Costa Rica Dome and the Peru Current. 2

+

Surface-Water Oxygen Consumption. Simpson and Zirino (103) observed that the p H of freshly upwelled seawater is distinctly lower than normal surface seawater; they used this characteristic to map the extent of freshly upwelled seawater off the coast of Peru. Other characteristics of freshly upwelled seawater are low chlorophyll, low temperature, low oxy-




202

Figure 12. Deep-sea oxygen-consumption rates at 3000 m under the Costa Rica Dome and the overlying phytoplankton biomass and productivity in the surface waters. The maxima of all three properties are close to the center of the Dome (i.e., 9°N, 89°W). These measurements were made manually.



10.

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gen, and high-nutrient salts (110). From the results of the CUE 11 cruise to the Oregon upwelling, one can add to this list the low rate of oxygen consumption and its equivalent, low metabolism (Figure 8). Seawater downstream i n an upwelling area is characterized by a high oxygen-consumption rate (high microbial metabolism), high chlorophyll a, high temperature, high p H , high oxygen, and low nutrients. Relaxed upwelling systems are characterized i n the surface waters by the water types normally found downstream i n an upwelling system, namely, high chlorophyll, high oxygen consumption rate, and temperature (Figure 9). The maps off Mauritanea partially reveal three bands of oxygen consumption i n an upwelling area (Figure 10). Bands of low oxygen consumption are discernable i n the freshly upwelled water and i n the distant offshore water; a band of high oxygen-consuming water lies i n between. During a relaxation period the inshore band is eliminated. This banding and its shift with changing upwelling conditions would have been revealed much better if the maps had been made in exactly the same location each time instead of being made i n different locations along the coast; however, when the sampling pattern was determined the short-term timedependence of upwelling was not recognized. Very likely the current investigation of the California upwelling (Organization of Persistent Upwelling Structures, an N S F research program at the University of Southern California) w i l l reveal, i n detail, this type of banding now that the short-term temporal variability i n upwelling systems is recognized and sampling is focussed on a single region, that is, Point Conception (4). The maps of the ocean off L o n g Point (Figure 5) show the plume characterized by high oxygen consumption and high chlorophyll. Furthermore, they provide evidence that outfalls in the vicinity of upwelling must discharge their waste below the upwelling source water, which may be much deeper than the average thermocline depth. Deep-Sea Oxygen Consumption. The deep-sea map of oxygen consumption under the Costa Rica D o m e reveals for the first time that the deep-sea is not homogeneous with respect to metabolism and the oxygenconsumption rate. The rate appears higher under the productive upwelled water of the Dome (Figure 12). This observation suggests a link between oceanic surface waters and the deep sea below, and infers that deep-sea shadows of other oceanographic surface features such as equatorial upwelling zones or the Antarctic convergence also w i l l be detectable by zones of enhanced oxygen consumption. The vertical profiles of oxygen consumption (Figure 11) (68) show that, i n spite of a connection between surface productivity and the deep water, most of the organic matter falling below the euphotic zone is oxidized i n the upper 500 m . This zone serves as a great biological filter that protects the deep sea from receiving more organic matter than it can metabolize. The deep waters below the Peru Current are already seriously



204


depleted of oxygen; only 2.4 m L / L of an original 7 m L / L remain. If more organic matter were to fall below 500 m the deep-water oxygen supply could be completely exhausted. So far we have connected E T S activity to oxygen and the oxygen-consumption rate. I n this context, it can also be used to estimate the speed of deep-sea currents and the age of the deep-sea water. Such estimates w i l l be in error to the extent that advection and diffusion are not considered. Nevertheless, they serve as an exercise that scales the role of deep-sea biological oxygen consumption, and this exercise is rarely done. T o make these estimates, prior knowledge of the current direction and the chemical properties of the water is needed. In the southeastern Pacific, the deep water east of the east Pacific rise at 2000 m has been observed to flow north (111) through passes i n the ridge system that separate the various basins i n this region (Figure 13). Furthermore, the deep-sea oxygen content decreases from basin to basin, starting w i t h the southeastern Pacific Basin below the Antarctic circumpolar current, and ending with the Panama Basin. A t the start of its journey i n the southeast Pacific Basin the 2000-m water contains

140°

120°

100°

80°W

Figure 13. Deep-ocean circulation through the ridges and basins of the southeastern Pacific. The east Pacific rise at 120° W provides an effective barrier to deep water penetrating eastward from the central Pacific. The stations, A and B, are referred to in the text. The figure was drawn from Lonsdale's (111) description of the deep waters of the eastern south Pacific.


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Ocean

3.25 m L of O2/L (111). By the time it reaches the southern part of the Peru Basin at 15° S it contains only 2.4 m L of 0 / L , having lost 0.85 m L of 0 / L along the way. W e measured E T S activity and calculated the oxygen-consumption rate for the water at 2000 m i n the southern part of the Peru Basin (68). Because of the high productivity of the Peru current upwelling, this rate is likely to be higher than comparable deep-sea oxygen-consumption rates in other parts of the southeastern Pacific. Nevertheless, by assuming that these rates are roughly representative of the deep-sea rates i n other basins and by assuming that advective and diffusive 0 losses were smaller than respiratory losses, we calculated both the current speed and the time required for the water to flow from the southeast Pacific Basin to the Peru Basin. Assuming a deep oxygen-consumption rate of 3.8 pL of 0 / L per year (68), we calculate that it would take 224 years to consume 0.85 m L of oxygen. Because the oxygen minimum is strongest along the eastern boundary of the Pacific, diffusion and advection would act to replenish the deepsea oxygen and minimize the observed depletion due to respiration along the trajectory of the current. Thus, 224 years is a lower limit. The distance between the study area and the starting point (Figure 13) is 4225 k m . Thus the water must have been flowing 19 km/year or 0.6 mm/s if it traveled 4225 k m in 224 years. This age only represents the time required for the deep water to flow from the northern part of the southeast Pacific Basin to the southern part of the Peru Basin. Because the oxygen at the starting point was already low (3.25 m L of 0 / L ) , significant oxygen consumption had already taken place i n the water from the time it started traveling north from the depths of the Circumpolar Ocean to the time it reached the northern part of the southeast Pacific Basin. This oxygen consumption and the total age of the water can be calculated from knowledge of deep-sea oxygen distribution. A t 2000 m under the Antarctic Convergence the water contains 5 m L of 0 / L (112,113). Thus 1.75 m L of 0 / L was lost i n transit to the southeast Pacific Basin at 40° S. A t JR = 3.8 pL of 0 / L per year, the transit time must have been 460 years. The total transit time from 70° S to 15° S would be 685 years. Similar ages (i.e., 750 and 900 years) were calculated for the 3000-m level under the Costa Rica Dome (54, 57). As mentioned before, such calculations i n eastern boundary regions w i l l yield low estimates of water-mass age because advection and diffusion have been ignored. 2

2


2

2

2

2

2

2

Acknowledgments This work was supported by N S F Grants OCE-75-23718 A O l , O C E 7718668, O C E 78-00610, and by O N R Contract N00014-76-C-0271. I thank Peg Colby and Pat Boisvert for enduring the many revisions of the manuscript, and J . Rollins for drafting all the figures. D . Harmon worked around the clock with me to map the Whites Point outfall and the Oregon


206


upwelling. J . Abrahamson constructed the automated system shown i n Figure 3 and used it i n mapping the Mauritanean upwelling. A . Westhagen and J . Rix interfaced the automated E T S system to the IRIS computer system (Coastal U p w e l l i n g Ecosystems Analysis program) i n the northwest A f r i c a experiment. J . Kelley was chief scientist and coordinated the mapping programs i n both the Oregon upwelling (CUE II) and the northwest A f r i c a (JOINT I) upwelling experiments. J . H . Vosjan and two reviewers made helpful suggestions that improved the manuscript between drafts, and D . Corson made thoughtful modifications that improved the final version. I am indebted to them a l l for their cooperation and assistance i n this


work. I also thank E . Green, the director of Office of Naval Research's chemical oceanography program, for supporting and encouraging the application of enzymology to the mapping of rate processes i n the ocean. This is contribution N o . 84023 from the Bigelow Laboratory for Ocean Sciences. Literature

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