JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. C9, PAGES 20,801-20,826, SEPTEMBER 15, 1999

Seasonalwater mass distribution in the Indonesian throughflow entering the Indian Ocean

C. Coatanoan,•'2N. Metzl,3 M. Fieux,4 andB. Coste•

Abstract. A multiparametricapproach is usedto analyzethe seasonalproperties of watermasses in the easternIndian Ocean.The data were measuredduring two cruisesof the JavaAustralia DynamicExperiment (JADE) programcarried out duringtwo oppositeseasons: August 1989 (SE monsoon)and February-March 1992 (NW monsoon).These cruises took place at the endof a La Nifia eventand during an E1Nifio episode,respectively. Seven sources have been identified in the studiedregion for the 200-800 m layer:the SubtropicalIndian Water, the Indian CentralWater, the modified Antarctic Intermediate Water, the Indonesian SubsurfaceWater, the Indonesian IntermediateWater, the Arabian Sea-PersianGulf Water (AS-PGW), and the Arabian Sea-Red Sea Water (AS-RSW). The selectedtracers are potentialtemperature, salinity and oxygenwith mass conservationand positive mixing coefficients as constraints. The analysisindicates the proportion of eachwater source along the Australia-Balisection and into the Indonesianchannels. Although no largechanges are observedfor Indonesianwaters, significant seasonal variations are found for the southernand northern Indian Ocean water. During the NW monsoon,the contributionof the AS-RSW increasesat the entranceof the Indonesianarchipelago whereas the contributionof the southIndian waters decreases in the northwestAustralia basin. In a complementarystudy, nutrients are introducedinto the multiparametricanalysis in orderto moreclearly separate the signatureof the northIndian waters (AS-PGW, AS-RSW) andto providesupplementary information on the biologicalhistory of the watermasses, which is comparedto large-scaleprimary production estimates.

1. Introduction locationsin the Indonesianseas, directly influencesthe water massdistribution in the Indonesianbasins [Gordon et al., 1994] The flow from the Pacific Ocean throughthe Indonesianseas as well as in the Indian Ocean [Wyrtki, 1961]. At an interannual marks the only tropical oceanic connection.This Indonesian timescale,the currentssupplying the Indonesianarchipelago are throughflowis consideredto havean importantrole in the global alsodisturbed by the australoscillations associated with E1 Nifio- oceanic circulation [Gordon, 1986; Schmitz, 1995]. The La Nifia events [Chiswell et al., 1995; Kindle and Phoebus, Indonesianthroughflow is drivenby a pressuregradient from the 1995; Picaut and Delcroix, 1995; Wijffelset al., 1995; Meyers, Pacific to the Indian Ocean [Wyrtki, 1961]. It is characterizedby 1996]. Beyond their influenceon the precipitation-evaporation large seasonalvariations due to differentwind patternsin the two balance,these events, through changes in the westernPacific sea basins, monsoon in the Indian Ocean and trade wind in the level,can also intervene on the Indo-Pacifictransport. westernequatorial Pacific [Bray et al., 1996]. The transportof The water massesflowing through the Indonesianseas and the throughflow,obtained from director indirect methods,varies from-2 to 22 Sv (1 Sv = 106 m3 s-1) [Piola and Gordon,1984; reachingthe Indian Oceanhave their origin mostlyin the North Pacific Ocean [Lukas et al., 1991; Godfrey et al., 1993; Gordon Fine, 1985; Fu, 1986; Gordon, 1986; Masumotoand Yamagata, et al., 1994]. The water massescrossing the "maritime continent" 1993; Fieux et al., 1994; Miyama et al., 1995; Fieux et al., basinsfollow two routes,the easternand westernroutes [Wyrtki, 1996a]; extrema correspondto the Java Australia Dynamic 1961; Gordon, 1986; Lukas et al., 1991; Fine et al., 1994; Experiment1989 (JADE 89) (SE monsoon)and JADE 92 (NW Miyama et al., 1995]. The Lombok Strait, with a sill depth monsoon)cruises. The maximum (estimatedfrom models) occurs from austral autumn to austral winter (SE monsoon), and the reaching350 m [Murray and Arief, 1988], allows throughonly upper waters coming from the Makassar Strait, whose surface minimumoccurs during the NW monsoon[Miyama et al., 1995]. watersoriginate from the upper thermoclineNorth Pacific water As a result, the seasonalcurrent reversal, observedin many [Gordon and Fine, 1996]. From the Banda Sea, two passages, situatedon both sidesof Timor island,allow the spreadingof the •Laboratoired'Oc6anographie etde Biog6ochimie, CNRS, Marseille, deeperIndonesian waters into the Indian Ocean[Rochford, 1966; France. 2Nowat Department of Marine Chemistry and Geochemistry, Woods Gordon,1986; Wyrtki, 1971]. Mixing takesplace in the different Hole OceanographicInstitution, Woods Hole, Massachusetts. Indonesianbasins [Van Aken et al., 1988; Ffield and Gordon, 3LaboratoiredePhysique etChimie Marines, INSU/CNRS, Universit6 1992, 1996] and stronglymodifies the propertiesof the waters Paris 6, Paris. flowing throughthe Indonesianarchipelago. Consequently, the 4Laboratoired'Oc6anographie Dynamique et de Climatologie,Pacific signaturehas completelyvanished in the water masses CNRS/ORSTOM/UPMC, Universit• Paris 6, Paris. when they enter the Indian Ocean, where we can define them as Copyright1999 by the American Geophysical Union. Indonesian waters [Fieux et al., 1996b]. From the south Indian Ocean,the centralwater and subtropicalwater, formed at 40øS- Papernumber 1999JC900129. 45øS and 25øS-35øS,respectively, are found in the northwestern 0148-0227/99/1999JC900129509.00 Australian basin [Wyrtki, 1971; Warren, 1981; Toole and

20,801 20,802 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

Warren, 1993]. Deeper, the Antarctic IntermediateWater is variations of water masses in the thermocline of the Indian Ocean ch•acterized by a salinity minimum (around 1000 m) that by using a set of historical data at large scale and defining appearsalso off the northwesternAustralian shelf [Wyrtki, 1971]. seasonal sources. Originating from the Red Sea [Rochford, 1966; Toole and In this paper,we apply the optimummultiparametric analysis Warren, 1993] or from the mixing of the Red Seaand the Persian at the regional scale, with the aim of detectingthe seasonal Gulf Waters [You and Tomczak, 1993; Fieux et al., 1994] and variation of the water massesin the Indonesian throughflow from the Arabian Sea, the Northwest Indian Intermediate Water enteringthe Indian Ocean. We use a closely spacedseries of flows eastward along the Sumatra and Java islands before stations obtained near and within the Indonesian Straits in the penetratinginto the Savu Sea [Wyrtki, 1971; Fieux et al., 1996b]. frameworkof the Java AustraliaDynamic Experimentconducted In order to quantify the contributionof the different water during two oppositeseasons. The cruiseswere carriedout at the masses to the observed data, an optimum multiparametric end of a La Nifia event and duringan E1Nifio episode,in August analysis(OMPA) was developedby Mackas et al. [1987] as an 1989 and February 1992, respectively.Therefore the seasonal extensionof the work by Tomczak[ 1981]. The principle of this study realized from this data set can take into accountlikely analysisis basedon an inversemethod that usesmeasurements of interannualeffects resulting from theseclimatic events.In order the concentrationof severaltracers to determinethe proportional to more clearly separatethe signatureof the north Indian waters, mixtureof the differentsource water typesthat best describesthe the nutrientswill be introducedinto the multiparametricanalysis. compositionof the water sample [Mackas et al., 1987]. Many An estimateof the effect of biological processeson the water applications,at regional or basin scales,have been undertakenin masseswill be madeby comparisonof the biogeochemicalresults severaloceanic regions. Thus Mackas et al. [1987] quantify the with large-scaleprimary production estimates. importanceof deep upwelling of California Undercurrentwater onto the continental shelf. Maamaatuaiahutapu et al. [1992] 2. Data attempt to visualize the different cores in the Brazil-Malvines confluence,where the water massesmix in a complexstructure. The JADE 89 and JADE 92 cruises, on board the R/V Marion At a larger scale, Hinrichsen and Tomczak[1993] describethe Dufresne of the Institut Franqais pour la Recherche et la water mass distribution in the northern Atlantic basin. Tomczak TechnologiePolaires (IFRTP), were carriedout in August 1989 and Large [1989] describedthe mixing between the Indian and February-March1992, respectively,in the easternpart of the Central Water and the Australasian Mediterranean Water (also Indian Ocean.The JADE 89 cruisetook place at the end of a La called Banda Sea Water or Indonesian Intermediate Water) in the Nifia event. February 1992 correspondedto an E1 Nifio episode. eastern Indian Ocean. You and Tomczak [ 1993] studied the water During JADE 89 (correspondingto the SE monsoon), 65 --'massesof the whole Indian Ocean thermocline with the same hydrographicstations were occupied,with 18 betweenAustralia method.These are mainly stationarysituations, which are studied and Bali and 21 off the channels(Figure 1). During JADE 92 • isopycnalhorizons. Recently, You [1997] studiedthe seasonal (correspondingto the NW monsoon),29 stationswere occupied

90øE 95øE 100øE 105øE 110øE 115øE 120øE 125øE 130øE 10øN . 10øN ß ¾ ' ø ChinaSea SuluSea

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ß 0o 6j ¾ 6.•62'6•'• •' 0o

ß . ß 58 5oSIndian Ocean 57 ,,•i" JavaSea ,' ' '• %ß BandaSea 5oS

. 55';4ß 53ß 52ß •;150 • . ß Sea . ß ß

j2 e 10øS '• 10øS 10øE 115øE 120øE 125øE • -• 5øs 12 ß .,, Timor Sea

9 ß

15øS 15os 10os

20os 15os 20øS

20os 25øS 25øS 90øE 95 øE 100øE 105øE 110øE 115øE 120øE 125øE 130øE

Figure 1. Locationof the stationsin the two JavaAustralia Dynamic experiment (JADE) cruises. COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW 20,803

220 2.5

below 2500 below 2500 rn 200 oC2 •80 • •.5

2

140_• *Jade 89 I • 0.5 o 0 34.6 34.65 34.7 34.75 34.8 34.6 34.65 34.7 34.75 34.8

Salinity Salinity

Figure2.. Comparisonof (left) oxygen concentrations (•mol kg-•), (right) potential temperature (øC), and salinity for both cruises below 2500 m.

between Port Hedland (northwest Australia) and Bali (Indonesia). where ki is the contributionor mixing coefficient of the water In addition,21 stationswere occupiedin the Timor, Roti, Savu, source, n is the water source number, Ci is the tracer and Sumba Straits. Both sections intersect all the waters carried concentrationof the water sourcei, and C,, is the measuredtracer from the Pacific Ocean throughthe lndonesianseas toward the concentrationin the seawatersample. Indian Ocean. These channelsrepresent all the possible ways In the seasonalstudy, all the parametersused are consideredto from the Banda Sea toward the Indian Ocean. The conductivity- be conservative.In principle, to describethe mixing of n water temperature-depth(CTD) dataset from JADE hasbeen discussed masses,n-1 conservative tracers are needed. Usually, the two by Fieux et al. [1994, 1996b]. Nitrate-nitrogen(NO3), phosphate- conservativetracers, temperatureand salinity, through 0-S phosphorus(PO4), and silicate-silicon(Si(OH)4) were measured diagrams,are usedto identify and track water masses.Insofar as on board during JADE 1989, accordingto Treguer and Le Corre geochemical tracers (dissolved oxygen and nutrients) are [1975] methodology,with an estimatedprecision of +0.1, +0.02 mathematicallyindependent of temperatureand salinity,they can and+0.1 /xmol kg -1, respectively. Nutrient data are available for be includedin the water masscontribution calculations. Although JADE 1989 only. In order to test the accuracy of the data nonconservative,the geochemicaltracers make it possibleto get obtained during the two seasons,we compared the deep supplementaryinformation on these water masses,taking care measurements(Figure 2). The averageof potential temperature, that conservationof hydrologicaltracers (including the continuity salinity, and oxygen concentration,below 4000 in in the equation)is respected.This is generallydone by weightingthe northwestern Australian basin, are 0.824 + 0.059øC, 34.712 + linear equationswith the inverseof the measurementerror and 0.002,and 194.62 + 1.23/xmolkg -•, respectively, for JADE 1989 checking the residuals of the system after inversion. An and 0.814 + 0.029øC, 34.712 + 0.004, and 194.22 + 1.54 /xmol alternativeapproach when usingnonconservative tracers consists kg'•, respectively,for JADE 1992.Since deep waters are not of taking into accountunknowns (ANC), which could represent affectedby seasonal(or interannual)variations, the comparison biologicalprocesses such as consumptionand remineralization of JADE 1989 and JADE 1992 data suggeststhat sufficient [Bolin et al., 1983; Metzl et al., 1989, 1990]. This offers a measurementquality has been achievedfor quantifyingseasonal decouplingbetween dynamical and biologicalprocesses, but at variations in the surface and intermediate waters. that stage,the unknownrepresents the total sumof the biological part without differentiation between the sources. When a biological unknown is added, the linear equation (1) is 3. Method transformedinto the following: A water mass is defined as a body of water with a common Z k, NCi + ANC = NCm (2) formation history of all its elements.A given ocean volume can t=l be sharedby severalsuch water bodies, which can penetrateeach The linear equationsystems (1) and (2) are transformedinto other as a result of mixing [Tomczak and Large, 1989]. the matricial system: Mathematically, water massesare described by a relationship Mx=N (3) describingthe different proportionsof the various water types and its associated set of standard deviations. Practically, the where M representsthe data vector attachedto each coefficient number of water types (called water sourcesin our study) for and tracer, x is the vector of the coefficients describing the each water mass is finite and small to fully representa water mixing of the sourcesand N correspondsto the data vector of mass. measuredtracers in the sample and the values attributed to For each tracer, the conservationequation can be expressed constraints. throughthe following linear equation: With this method, we use a strict equation to provide mass • kiCi = C m (l) conservation:Zxi = 1. This equationwill be representedin its i=1 matricial form and mustbe exactly satisfied: 20,804 COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

Ex =f (4) 4. Water Mass Analysis and Source Characterization where E is the matrix of order (1, n) with n the number of source water types;x is the solutionvector (n, 1) giving for eachsample The Australia-Balisection is locatedat the boundaryof water the bestfitting fractionalcontribution of each sourcetype. It must masses from the Indian Ocean and the Indonesian seas. Several minimize the sum of squaresof deviationbetween the measured data analyses,from the two JADE cruises,were presentedby data and the estimatesof modelparameters. Here f is the vector1 Fieux et al. [1994, 1996a, b], Molcard et al. [1994, 1996], and expressingthe conditionof massconservation. C.Coatanoan et al. (Nutrients distribution in the Indonesian The tracerswill obey the conservationequations (1) (and (2) straits and along the Sumatra and Java islands during the for the nutrients),which are approximatelysatisfied in a least southern monsoon, submitted to Oceanologica Acta, 1997). squaressense. This canbe written: Previous studiesby Rochford [1963], Wyrtki [1971], Tomczak and Large [1989], You and Tomczak [1993], and You [1997] Ax•b (5) madeit possibleto definethe watermasses mixing in the eastern where A is the sourcedefinition matrix (p, n) with p tracervalues Indian Ocean basin. Figures 3a-3i illustrate the observed for n sourcewater types;b is the column vector (p, 1) with the potential temperature,salinity, oxygen, phosphate,nitrate, and first p elementsequal to the measuredconcentrations of the tracer silicatedistributions along the Australia-Balisection, using only variablesin a samplethat is assumedto be a mixture of the the bottle measurementsthat correspondto the quantitative sourcewater typesdescribed by A. analysisapplied in thispaper and showboth seasonsside by side. The convex constraintsthat expressthe nonnegativityof the coefficient,xi > 0 for all i, areadded to thematricial systems (4) 4.1. Australia-Bali Radial: 0-1000 m Layer and (5): The mostpronounced structure, observed during both seasons, Gx>h (6) is the sharphydrological front around 13øS-14øSwell definedin salinity, oxygen, and nutrients (Figures 3c and 3d). This front where G is the unit matrix of order (n, n) and h is the null vector reachesthe surfaceduring the NW monsoonand is coveredby a (1, n). Such convex constraintswill be applied to mixing low-salinity layer during the SE monsoon.South of the front, a coefficientsas well as to biological unknowns,with negativity salinity maximum (Figures 3c and 3d) is observed above an constraintsfor the oxygen and nonnegativityconstraints for the oxygenmaximum (Figures3e and 3f) associatedwith minima in nutrients. nutrients (Figures 3g, 3h, and 3i). The salinity maximum The system(4), (5), (6) is normalizedand solvedwith the least correspondsto the SubtropicalIndian Water (STIW) [Warren, squaresmethod with an algorithm of equality and inequality 1981; Fieux et al., 1994]. Betweenthe two coresof high salinity, [Lawsonand Hanson, 1974]. The output vectorx is the resultof a detailed analysisof the hydrology indicates mixing with the the inversion. Its stability is tested by numerical perturbation lower salinity Indonesianwater [Fieux et al., 1994]. During the experiments.They consistof adding random deviationsto the SE monsoon,the salinity maximum (S>35.1) is associatedwith measured data (vector b) and the elements of the matrix A. The minimain phosphate(PO4<1.20 /.tmol kg-1), nitrate (NO3<15 absolutevalues of the imposeddeviations are lower than or equal /.tmolkg-1), and silicate concentrations (Si(OH)4<20 /.tmol kg -1) to the estimated standard deviation values of the considered (Figure 3i). Deeper, the oxygen maximum defines the Indian tracervariables. Thirty perturbationsgive a mean solutionvector Central Water (ICW) [Warren, 1981; Toole and Warren, 1993; x for each sample.The studyof the standarddeviations leads to Fine, 1993; Fieux et al., 1994], also called Subantarctic Mode an evaluationof the coefficientvalidity and to concludewhether Water [Warren, 1981]. The northeastwardextension of this water or not seasonal variations are significant according to massappears mostly bounded by the hydrologicalfront observed measurementerrors and a priori definition of the sources.The in the Australia-Bali section and limited to the NW Australian systemto be solvedat eachperturbation is: basin [Fieux et al., 1994, 1996b]. Like the STIW, the ICW is not (A + AA) x'= (b + Ab) (7) homogeneousand separatedin two cores,located at 17ø30'S and 14ø30'S during both seasons.In these cores,the oxygen values To get informationabout nonconservative behavior of tracers arehigher at theSE monsoon(O2>180 /.tmol kg -1) than at the and possibleerrors due to the sourcewater typesdescription and NW monsoon(O2>150 /.tmol kg -1) (Figures3e and 3f). Low uncertainties associated with the measurements, a vector R of nutrientvalues (PO4<1.6 p. mol kg-1, NO3<25p. mol kg-1, and error on the tracer is calculated. This vector R of residuals is the Si(OH)4<30/.tmolkg-1) are associated with the oxygen maximum. differencebetween the predicted(Ax) and the measured(b) data. Between750 and 1000 m, a salinity minimum (34.58-34.61) has This vectoris definedby the followingmatricial system: been detected[Fieux et al., 1996b, Figure 3c]. This signalis not apparentin salinity classeschosen here (Figures 3c and 3d). R = Ax - b (8) Close to the Australian continental shelf, it could be a faint with x the average of the x' obtained from the thirty signatureof the Antarctic IntermediateWater (AAIW) influence perturbations. [Fieux et al., 1994]. In the north, it correspondsto mixing with Thus, in the ideal case, when the source water type the Indonesian waters coming particularly from the Timor descriptionsare correct and complete, the measurementsare Passage[Fieux et al., 1996b]. unbiased, and the tracers are conservative, the vector R must be North of the frontal zone, near Bali (Figures3c and 3e), high zero. The analysisof the spatial distribution of residualswill salinities(>34.65) and low oxygenconcentrations (<90/.tmol kg- allow us to selectthe oceanlayers for which origin and mixing of 1) characterizethe watermasses originating from the North water massescan be discussedaccording to steady state and Indian Ocean (as mixing of the Persian Gulf Water (PGW) and tracer conservationassumptions. For this seasonalanalysis, only the Red Sea Water (RSW) with the Arabian Sea Water). High the first 1000 m of the water column will be studied. nutrientvalues (PO4>2 /.tmol kg '1, NO3>30/.tmol kg -1 and COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW 20,805

a) PotentialTemperature Jade 1989 b) PotentialTemperature Jade 1992 2 3 4 5 6 7 $ 9 l0 It 12 1•14 15 16 17 I0 2 3 4 5 6 7 $ 9 10 Ii 12 13 14 15 16 17 i$ 19 20 21 22 2314 '2_q26 2•$

28 26 24 100 22•-• ' • 20• 20-'-•• 18•• 18•"•'•'• 16 200 16• 16• 14

14•14• 12

300

400 1o• 1o•

500

600

700

800

900

1ooo -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude øS Latitude øS

c) Salinity Jade 1989 d) Salinity Jade 1992 2 3 4 5 6 7 S 9 i0 II 12 I '•14 !'• 16 17 I0 2 3 4 5 6 7 $ 9 10 ii 12 13 14 15 16 17 !$ 19 20 21 22 23 24 '2.526 2•$

100 t4.1

200 (

34 7 34.8 300 '3J6 34.5

400 34

34.7 34.7 500

34.6 600 4.•4'7 34.6 700 •34/6 7 .6 800 34 6

I 346• 9OO '-'"-'•• 34

1ooo -19 -18 -17 -16 -15 -14 -13 - 2 -11 -10 -9 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 Latitude øS Latitude øS Figure3. Verticaldistribution on theAustralia-Bali section of thebottle data for a) potentialtemperature (øC) Jade 89,b) potential temperature (øC)Jade 92, c) salinityJade 89, d) salinityJade 92, e) oxygen (gmol kg -•) Jade 89, f) oxygen(gmol kg 'l) Jade92, g) phosphate (gmol kg -1) Jade 89, h) nitrate (gmol kg 'l) Jade89, i) silicate(!amol kg-1) Jade 89. 20,806 COATANOANET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

e) Oxygen Jade 1989 f) Oxygen Jade 1992

2 3 4 5 6 7 $ 9 10 II 12 1314 15 1617 l0 2 3 4 5 6 7 $ 9 10 11 12 13 14 15 16 17 15 19 20 21 22232425262728

100 lOO

200 120 2OO liO

120 300 300 lOO

100

400 400

90 500 500

6O0 11o 600

90

700 700

800 800

900 900

1000 1ooo -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude øS Latitude øS

g) PhosphateJade 1989 h) Nitrate Jade 1989 i) Silicate Jade 1989

2 3 4 5 6 '7 8 9 10 It 12 131415161'719 2 3 4 5 6 '7 8 9 10 11 12 131415161• 19 2 3 4 5 6 7 $ 9 10 11 12 131415161• 19

0 r•• •.••0•0'•]5 5 • •' •10•• lO0--•- j600••.••• ,oo

300 1.4 1.6 1.8 300 400 500 600 . 600

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900 .6 4000800 3•• • •09• 3090 •0 10009001, ...... 1000 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -18 -17 -16 -15 -14 -13 -12-11 -10 -9 -18 -17 -16 -15 -14 -13 -12-11 -10 -9 Latitude øS Latitude os Latitude os

Figure 3. (continued)

Si(OH)4>40tzmol kg -•) areassociated with the salinity maximum In the middle of the section,low and homogeneoussalinities (Figures3g, 3h, and 3i). A slightincrease of the salinityin Timor (Figures 3c and 3d), particularly marked between 13ø30'S and Strait could be assignedto a faint influenceof this water mass 11øS (34.59-34.60), indicatethe direct input of the throughflow [Fieux et al., 1996b]. Although this water mass has not been waters [Fieux et al., 1996b]. The low salinities of Indonesian previouslydetected inside the Indonesianarchipelago [Broecker SubsurfaceWater (ISW) and the Indonesian Intermediate Water et al., 1986; Van Aken et al., 1988; Van Bennekom, 1988], it has (IIW) at depth, are transportedthrough Timor and Ombai Straits, been shown to enter the Savu Sea [Fieux et al., 1996b]. which draw Indonesian waters from the eastern and western COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW 20,807

Table la. Data for Water Typesof the AustralasianMediterranean Water or IndonesianWater (AAMW), Indian Central Water (ICW), North Indian Central Water (NICW), and Red Sea Water (RSW)

Potential Temperature, Salinity, Oxygen, Phosphate, Nitrate, Silicate, Density, øC psu #mol kg 4 #mol kg 4 #mol kg 4 #mol kg 4 Tomczakand Large [ 1989] WT1 AAMW 20.00 34.566 124.14 0.810 11.954 7.697 24.4 WT2 AAMW 5.00 34.581 93.50 2.307 37.647 73.906 27.3 WT3 ICW 15.00 35.624 237.78 0.255 0.201 0.754 26.4 WT4 ICW 8.00 34.540 242.85 1.140 17.960 5.353 26.9 You and Tomczak [1993] ICW 18.16 35.624 278.72 0.145 2.921 25.7 ICW 9.07 34.805 214.19 1.327 10.089 26.9 ICW 4.39 34.384 177.61 1.936 43.879 27.3 NICW 15.27 34.840 2.68 2.099 25.594 25.7 NICW 7.80 35.098 32.42 2.796 60.179 27.3 AAMW 14.89 34.774 112.86 1.615 28.638 25.7 AAMW 5.55 34.521 98.61 2.662 79.103 27.3 RSW 25.90 38.082 161.90 0.372 0.701 25.7

Banda Sea, respectively [Hautala et al., 1996]. This water is SubtropicalIndian Water and oxygen maximum (250 ttmol kg -1) relativelyrich in silica(Si(OH)4>60 /•mol kg-• in the Timor for the Indian Central Water. A third Indian water mass trench [Van Bennekom,1988]). The high percentageof diatoms correspondsto the modified Antarctic Intermediate Water. This in the euphoticzone of Indonesianwaters involves an important water has been defined at a latitude (35øS) where its properties assimilationof dissolved silica in the surface water, especially are already modified. For the Indonesian waters, the during the SE monsoon characterizedby high productivity in characterizationis given by the diagramscorresponding to the these basins [Van Bennekom, 1988] and the sedimentation of the stations occupied in the straits (Figure 5). The Indonesian diatom frustules in the water column. Their dissolution leads to a Subsurface Water and the Indonesian Intermediate Water significantsilica input into the IndonesianSeas. Consequently, correspondto the Indonesianwater of the upper thermoclineand silicate may be an important tracer for separatingthe various to modified intermediatewater of the Banda Sea, respectively, water masses present at the eastern boundary of the Indian when they enter into the Indian Ocean. For the North Indian Ocean. Ocean waters,we define two sourcesfrom historic data diagrams [Wyrtki, 1971]: the Arabian Sea-Persian Gulf Water and the 4.2. Characterization of Source Waters for the Arabian Sea-Red Sea Water, taking their characteristicsin the 200-800 rn Layer northwesternand western Arabian Sea, respectively.From the In the water mass analysisabove, excluding the deep waters, Jadedata, a salinity maximum(>35.1 at 250 m near the equator) we have mentionedsource waters with correspondingproperty anda minimumof oxygen(53.6 ttmol kg -1 observed along the extremes: STIW, ICW, modified AAIW (m-AAIW), ISW, IIW, Sumatraand Java coastaround 700-800 m) show the presenceof Arabian Sea-PGW (AS-PGW), and Arabian Sea-Red Sea Water both sources along Sumatra and Java. The upper salinity (AS-RSW). Consideringthe core layersof thesesources [Wyrtki, maximum originates from mixing between the Persian Gulf 1971], the historic data compilation [Rochford, 1963; Tomczak Water entering north of the Arabian Sea and the high-salinity and Large, 1989; You and Tomczak,1993; You, 1997] (Tables la waters typical of the high evaporationobserved in the Arabian and lb) and the Jade data with their 0-S and {)-02 diagrams Sea. Deeper, the salinity maximum characterizesthe mixing (Figure 4), we are able to characterizethe seven sources(Table between the Arabian Sea Water and the Red Sea Water. Their 2). For the southern Indian waters, each source will be characteristicsin this studyare taken in the Arabian Sea at 250 m characterizedby an extremum:salinity maximum (35.80) for the in a region near the outputof the PersianGulf and 600 m near the

Table lb. Data for Water Types From You [1997]

Potential Temperature, Salinity, Oxygen, Phosphate, Nitrate, Silicate, Density, øC psu # molkg -• # molkg 4 # molkg 4 # molkg -• c•0 SW NE SW NE SW NE SW NE SW NE SW NE

ICW 18.15 18.17 35.62 35.62 265.3 260.8 0.06 0.05 - - 1.57 1.13 25.7 ICW 9.21 9.39 34.79 34.80 225.5 222.4 1.29 1.36 - - 8.06 8.87 26.9 ICW 6.56 6.77 34.55 34.56 213.9 210.8 1.66 1.76 - - 21.39 22.49 27.1 NICW 15.60 15.70 34.84 34.85 3.1 1.8 2.13 2.12 - - 21.44 23.34 25.7 NICW 9.29 9.17 35.05 35.03 23.2 24.1 2.84 2.67 - - 58.59 58.49 27.1 AAMW 14.96 14.93 34.64 34.63 117.4 117.0 1.41 0.97 - - 22.94 22.01 25.7 AAMW 14.93 6.90 34.56 34.59 102.7 103.1 2.41 1.78 - - 80.08 58.67 27.1 RSW 27.60 19.23 39.21 35.97 187.1 74.6 0.12 1.85 - - 1.07 14.12 25.7

Seasonalvariations, according to the SW and NE monsoon,are definedby You [ 1997]. 20,808 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

35 + JADE 89 ß JADE 92 [] SOURCES

30

• 25 o

• 20

• 15

o 10

33 33.2 33.4 33.6 33.8 34 34.2 34.4 34.6 34.8 35 35.2 35.4 35.6 35.8

Salinity

35

JADE 89 ß JADE 92 [] SOURCES

30

? 25

• 20

• 15

o 10

0 50 100 150 200 250 Oxygen(#mol kg 4)

Figure 4. The (top) 0-S and (bottom)0-O2 diagramsfor all stationsof JADE 89 and JADE 92 (bottle data). Squarescorrespond to the locationof the sources.Stippled lines indicate the limit studycorresponding to the 200- 800 m layer.Abbreviations are definedas follows:ISW, IndonesianSubsurface Water; STIW, SubtropicalIndian Water; ICW, Indian Central Water; m-AAIW, modified Antarctic IndonesianWater; IIW, IndonesianIntermediate Water; AS-RSW, Arabian Sea-Red Sea Water; and AS-PGW, Arabian Sea-Persian Gulf Water. output of the Gulf of Aden for the AS-PGW and AS-RSW, perturbationshave been realized at each station. A relative error respectively. is associatedwith each tracer accordingto measurementsand source values (Table 2) and is taken into account for each 4.3. Uncertainties perturbation.These errors represent,for each sample, the To discussseasonal variation of mixing coefficients,we first variabilitydue to the measurementuncertainties and the temporal need to examinethe possibleerrors on thesecoefficients. Thirty (interannualscale) and spatialvariations for the defined sources. COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW 20,809

Table 2. Tracer Water Source Characteristic and Relative Errors

STIW ICW m-AAIW ISW IIW AS-PGW AS-RSW Characterization Measured Value Error Error

0, øC 18.2 10.2 4.4 20 5.2 15 10 0.05 0.001 Salinity 35.80 34.80 34.38 34.48 34.59 35.80 35.3 0.005 0.001 02,#mol kg -I 223.3 250.1 196.04 125.0 93.79 9 22.33 0.05 0.02 PO4,#mol kg 'l 0.2 0.8 2.0 0.8 2.6 2.4 2.6 0.1 0.05 NO3,#mol kg -• 2 8 20 10 32 20 30 0.1 0.05 Si(OH)4,#mol kg 'l 8 8 22 10 85 30 50 0.1 0.05 IJ0a 25.83 26.76 27.25 24.37 27.33 26.59 27.18 Abbreviations are defined as follows: STIW, Subtropical Indian Water; ICW, Indian Central Water; m-AAIW, modified-Antarctic Intermediate Water; ISW, Indonesian Subsurface Water; I1W, Indonesian Intermediate Water; AS-PGW, Arabian Sea-Persian Gulf Water; and AS-RSW, Arabian Sea-Red Sea Water. aThe density has been calculated from the equation of stateof seawaterwith tracer values defined in thistable. (reference pressure= 0dbar)

The standard deviation, computed from the multiparametric particularlyin the surfacelayer, which is not taken into account analysisand associatedwith each mixing coefficient, expresses here. When residualsare positive,tracer value is overestimated, the variation of the water mass from the steady state, which is and, inversely, negative residuals correspond to an consideredto characterizethe sources.High standarddeviations underestimation.The significantresiduals in surfacelayer are are mainly observedin the zone where the defined sourcewaters explained by the local nonconservationof these tracers. The do not mix. Weak standarddeviations are observed at depths biological activity, intense in the euphotic zone, acts like a where the sourcesare the best represented. precursorof the nutrient sink and dissolved oxygen source. During the SE monsoon,on the Australia-Bali section and Potential temperatureand salinity residualsshow that for a heat from 200 to 800 m, the uncertaintyof the coefficientsis 6.2%, gain thereis a massloss (positive salinity surface residuals versus 0.1%, 2.2%, 0.4%, 0.8% and 9% for STIW, ICW, m-AAIW, negative potential temperaturesurface residuals). Between 200 ISW, IlW, and AS-RSW, respectively(AS-PGW is not presented and 800 m and for both seasons,the residualsare low, indicating in this section).For the NW monsoon,the uncertaintyis 4.5%, that defined sources are well adapted for this layer. 1.5%, 2%, 0.5%, 0.8% and 2%, respectively.These values have Consequently,the analysisof the resultswill be discussedonly been calculated at the locations where the sources have the for the 200-800 m layer. highestcoefficients on the section.They give the confidencelimit of the mixing coefficients and allow us to determine if the 5. Results of the Inversion: SeasonalComparison seasonalvariability is meaningful. The results of the inversion with seven sources, three tracers (potential temperature, salinity, and dissolved oxygen), and 4.4. Residuals continuity (massconservation), are presentedin the Figures 7, 8, The residual vector on the tracers (see (8)) shows high 9, and 10. They show the proportionsof each sourcealong the absolutevalues for some layers of the water column (Figure 6), Australia-Bali section and in the Indonesian Straits.

30 30• i,ndon,esia,nstr,aits, ,

• 25

o

• 20 20

• 15 • ' ' I-•Z+' ' .... • 10 • 10•', ', .•:•, ', +Jade89 ', ', ' ' - 26.5-' ' ' :'•' [, .½?-.• ', ', ßJade 92 8•%

• ' IIW '"%+• , , ', []JadeSourCes 92 ....27 5" ' ''*'•%:% • o 'o •"• • • ' o 60% ,

ß . 0

33.5 34 34.5 35 50 100 150 200 250 Salinity Oxygen(#mol kg 4) Figure 5. The (left) 0-S and (right) 0-02 diagramsfor stationsin the IndonesianStraits (bottle data). Squares correspondto the locationof the sources.Stippled lines indicatethe limit studycorresponding to the 200-800 m layer. 20,810 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

Potential temperature residuals (øC) Potential temperature residuals (øC)

-12 -10 -8 -6 -4 -2 0 -12 -10 -8 -6 -4 -2 0

oo o

-200 - -200

o

-400 - -400 - o o

-600 - o -600 - JADE 89 JADE 92 0 0 north of front -800 - -800 - o north of front o o south of front ß south of front c•o

-1000 -1000

Salinity residuals Salinity residuals

-1 0 1 -1 0 1

0 0

-200 - -200

-400 - -400

-600 - -600 JADE89 JADE 92

-800 - north of front -800 D o north of front o south of front c• ß south of front

-1000 c• -1000

Oxygenresiduals (#mol kg'. •) Oxygenresiduals (#mol kg -1)

-30 -25 -20 -15 -10 -5 0 5 -30 -25 -20 -15 -10 -5 0 5 0 o o (:],o o

-200 -200

o

-400 -400

-600 - o -600 JADE 89 0 • JADE92 north of front -800 - • onort south of front • ß southof front

-1000 • -1000 [

Figure6. Residualsof (top)heat (øC), (middle) salinity and (bottom) oxygen (•mol kg -l) for (left)JADE 89 and (right) JADE 92 in the Australia-Bali section. COATANOANET AL.' WATER MASSDISTRIBUTION IN THROUGHFLOW 20,811

ISW Jade 1989 ISW Jade 1992

2 3 4 5 6 '/ $ 9 10 11 12 131415161'/ 19 -200 •'• o.•• o.s•• , ,;• -200 -30O • • •• o.•• -• -3oo • •o.2• •o.3 • _ -400 'o •-400 -500

-600 0A • -600 Ol

-700

-800 ...... ' ß -800 -18 -17 -16•* .-15•* -14 ••- -13 -12 -11 -10 -9 •-500 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude (øS) Latitude (øS) IIW Jade 1989 IIW Jade 1992

2 3 4 5 6 7 8 9 10 11 12 1314 15161'/ 19 4 5 6 7 $ 9 10 11 12 13 14 15 16 17 15 19 20 21 22232425262728 -200 -200 ' -300 • -300

ß . ß ß ß • -400 -400 .... 0...... 0.6- -500 -5oo • ß /06/08 ' 08 0.7 o4•Z// ' '. -600 •x•o.o ••• • x , -600 -700 • o.8•• ...... ß• -700 . . . ß ß ß . . + ß . + ß . + . ß

-800 -0.9. ,, -• 0.9. . ,• -,•.;,I -800 01,9 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude (øS) Latitude (øS) AS-RSW Jade 1989 AS-RSW Jade 1992

2 3 4 5 6 7 $ 9 10 !1 12 131415161'/19 4 5 6 '/ $ 9 10 11 12 13 14 15 16 17 15 19 20 21 22232425262728 -200,...... i , r -300 .

=-600 '0.1.... o,l: =-'øø-600 0.1 .

-800-7oo[ß i ]i• ' ' i :•' .....ß , , •r i t o.•'' ' i' •'+l * •'' + I -7oo-800I • ..... ,'.,',ß .'','.' , -18-17 -i6 -i'5-14 -13 -12 -11 -10 -9 -18-17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude(øS) Latitude(øS) Figure7. Mixingcoefficients of the Indonesian and North Indian water masses in theAustralia-Bali section for (left)JADE 89 and(right) JADE 92. ArabianSe-Persian Gulf Water (AS-PGW) is notdisplayed because it is not present.

5.1. Indonesian Waters monsoon and between 11ø30'S and 13ø30'S for the NW monsoon. A decrease in the coefficient is observed at the latitude The IndonesianSubsurface Water is presentin the thermocline of the hydrologicalfront only for the NW monsoonand at the of theAustralia-Bali section (Figure 7) with highervalues (60%). surface'an accumulationof low-salinitywater is observednorth The ISW is situated between 10ø30'S and 14ø30'S for the SE of 13ø30'S(Figures 3c and 3d). Godfreyand Ridgway[1985] 20,812 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

STIW Jade 1989 STIW Jade 1992

2 3 4 5 6 7 $ 9 10 11 12 131415161719 4 5 6 7 -200/ ...... -200 \-"$" 9 10 11 12 13 14 15 16 1'/ 15 19 20 2122232425262'/28

-400 'o.•..•'...... ß • -400 ß ß -500 ...... i•-5oo ß ß......

-600 ...... ' ? • -600 '...... -700 ...... '• -700 . ß...... -800-i8'-'i7'-i6'-[5'-14'-i3'-i•" i'l"-'i•)"'-½ -800 -i8'-i7'-i6'-i5'-i4"-i'3'-•2'-il "-•0"-9 Latitude(øS) Latitude(øS) CIW Jade 1989 CIW Jade 1992

2 3 4 5 6 7 $ 9 10 11 12 131415161'/ 19 -200 -200 45 6 7 $ 9 1011 12 13 l• 1516 17 18 19 20 21 2223242526T/•8 -400-3oo L (•o.• ß...... 300 -500 ß•' ß . ß ßß ß '. , •-500 d.• ...... -600 ...... ß ,• • -600 '......

-700 ...... ' .' • -700 -800-i8'-'i7'-i6'-i'5'-•4'-i3:-i•" i'l"-'i•)"'-; -800 -i8'-i7'-i6'-i5'-i4"-i'3'-•'2'-i1"-10"-9 Latitude(øS) Latitude(øS) m-AAIW Jade 1989 m-AAIW Jade 1992 -200•'2 3/ 4...... 5 6 7 $ 9 ' 10...... 11 12 1314151617 19i -200[4 5 ...... 6 7 }51,617 1519 20 2122232•25262'17.$ -300' o.1 1.0.1 o.t . •' -400 -400 ' .... • t .... 0.2.

tL¾' ' ß ...... ch ß :...; o ...... -600]'-,,Xo.,•o.•• ...... + •, ;::h-600 -. t ...... ' ß' • -700. ß...... -800-•8-•7-i6-i'"'" .... 5' -4-13-12-11-10 • .... '"' ....""' -9•: -800-18-17-16-15-14-13-12-11-10...... , ..... ,..,-9 Latitude(øS) Latitude(øS) Figure8. Mixingcoefficients of the South Indian water masses in theAustralia-Bali section for (left)JADE 89 and (fight) JADE 92. showthat part of the SouthEquatorial Current transports Current. During the SE monsoon near the Bali coast, an uplift of Indonesianwaters westward, onthe latitude close to 10øS[Fine, themixing coefficient lines corresponds to the presence of 1985],and that a fractionof the IndonesianWater flows upwellingduring this season. The salinity distribution, north of southwardalong the West Australian coast in the Leeuwinthe Australia-Bali section [Fieux et al., 1994,Figure 3c, 1996b, COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW 20,813

ISW Jade 1989 ISW Jade 1992 35 39 3•28 33•31 41 23 22 21 20 36 35 34 ' 3230 3050424.746 45A 3 51 50 49 48 36353• 4•92.726 Z54 , -200 • '-• 0.5•7-•.5 •'-- ,•._...... • . i -- 0.4 • 0.4 --- -2oo. ).5 .'v-,,•0;5 • •-'0.•• ?.4o5 o.4,w- o.4--- o.• --0.3 '•'-- 0.3 • -300 0.4. -.,•- 0.4;-,•,. 0.4 -3000•.• • 0.3•'0.3'--'0.3 3,,Z- 0.•-- • 0.2.'-'7- 0.2 • • 0.2 0.2 ' -400 . 2• 0.2"•'o.i • o.: -400 • 0.2, .. -500 ...... -500 (•.1 -600 .•_.•o.•--- o.•---- o.1 -600 D,1'-'• 0'.1

-700 -' ß -700 . .

-800 ß , -800 "' • , -11 -io -9 -11 -9 Latitude (øS) Latitude (øS) IIW Jade 1989 IIW Jade 1992 38 30 3•'28 33831 41 23 22 21 20 36 35 34 3230 3050424'746 45A 3 51 50 4948 363534 %26 , i -200b ø.•' _--7•.5---- 0.5- 4_0.5 • 0.5•_ 0.5 • ' r-'-"0.6-----0' - 0.3-• o.s--- _._..0.t5 -- 0.6 • 0.6 -200]••).5:'"-• o.:ß ß o.d• o.( -300 b.6• 0.6...... -300 ' ' o:•4- 5• ).7• 0.7• 0.7• 'o.72•0.2 5"• -400 ...... 0.3 -400-- '0.7, ' . 3.7 0.7 -500 0.7 -500

-600 ' •6.8 ' -600 ,.8'x' 0'.7

-700 -0.9• ß ' -700 - 0.9 • 0.9 -- 0.9 -0.9 • 0.9

*. t 4. ß , , -800 , 1 -800 -11 -10 -11 -10 -9 Latitude (øS) Latitude (øS) AS-RSW Jade 1989 AS-RSW Jade 1992 38 39 3•'28 33831 23 22 2l 20 36 35 34 3230 305{•124'746 45A 3 -200 363534 4•2.726 2• -200

-300 -300

-400 ß ß ... ß.•0.1 0.1' -400 •.1.. -500 -500

-600 '"o.ß 1 ß •' -600 • 0.1 * 0.1-

-700 -700

-800 , , , ' .' , -800 '. ' '• -11 -lO -9 -il -10 Latitude (øS) Latitude (øS) Figure9. Mixingcoefficients of the Indonesian and North Indian water masses in the section of theIndonesian Straitsfor (left) JADE 89 and (right) JADE 92.

Figure3c], is in agreementwith the decrease of theproportions seasons) are observedbelow 300 m in the northernpart of the of the IIW near the Bali coast,which is replacedby the water section (Figure 7). The gradientof isolines showingthe comingfrom the North Indian Ocean. hydrologicalfront is strongerduring the NW monsoonthan Between Australia and Bali, around 300-350 m, the IIW duringthe SE monsoon,possibly owing to closerstations for the graduallyreplaces the ISW. High values(> 55% for both NW monsoon.South of the front (Figure7), between200 and 20,814 COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

95øE 100øE 105øE 110øE 115øE 120øE 125øE 5øN 0. 5øN

SaraSea ,. 5os

ß.ß ' -"<:2:3 0os ß ß

15øSi IndianOcean . 15øS .. AS-PGWSigma0 = 26.5 ß

20øS ...... i ...... (around 300 ._...... m) ...... _:...... ' 20øS 95øE 100øE 105øE 110øE 115•E 120øE 125øE

95øE 100øE 105øE 110øE 115•E 120øE 125øE 5øN 0, 5øN

,,.!

o

/..-0.4 0.35.q'• Java Sea

,,

0.35.

10øS• 0.3 10øS I

15:'Si IndianOcean 15øS i AS-RSWSigma0=27.0 ': • 20øSi• (around500m) ' 20øS 95øE 100øE 105øE 110øE 115øE 120øE 125øE

Figure 10. Isopycnaldistribution of themixing coefficients of thenorth Indian water masses for JADE 89 at (top) 300 m and (bottom) 500 m.

600 m, the IIW appearsin slightlyhigher proportions during the AAIW (Figures 7 and 8). Near the Bali coast, a decreasein the NW monsoon.In 1992 (NW monsoon),the currentsare stronger IIW mixing coefficientis more prominentduring the NW and more irregularthan in 1989 (SE monsoon),suggesting an monsoon.This decreaseis linkedto theincrease in theproportion eddy-like circulation,leading to intense mixing between the of water coming from the North Indian Ocean. different waterscoming from the southernIndian Ocean and the In and off the IndonesianStraits (Figure 9), the distributionof Indonesian seas [Fieux et al., 1996a]. Below 600 m, the front theISW is identicalfor bothseasons, without significant seasonal definedby the mixing coefficientsdisappears and IIW, at more variationsof the mixing coefficients.For IIW, few differencesare than 80%, occupiesthe entire width of the section. Near the observed between both seasons. At the northern outflow of the Northwest Australian Shelf during the NW monsoon, the Savu Sea, 70% of the IIW is observed at 300 m for the SE proportionvalues decrease, which is linked to the intrusionof m- monsoon and at 450 m for the NW monsoon on the southern side COATANOAN ET AL.: WATER MASS DISTRIBUTION 1N THROUGHFLOW 20,815

(Figure9). The sectionsoff the IndonesianStraits, during the SE 8) which is surprisingat those depths.It appearsinside a core monsoon, were outside the straits. Near the Sumbawa coast, the between 350 and 650 m in 1989. In 1992, this water spreads decreasein the proportionof I1W observedbetween 400 and 700 between 300 and 700 m from the Australian coast to the front. m is explainedby the introductionof the water originatingfrom Rochford [1963] showsthe presenceof AAIW in the Indonesian the North Indian Ocean,particularly for the NW monsoonwhen Straitsbut suggeststhat the hydrologicalcharacteristics of AAIW the station measurements were conducted in the strait itself. and the Indonesianwaters are difficult to separate.Fine [1993] shows that some of the recently ventilated AA1W appearsto 5.2. South Indian Waters spreadboth north and northeastward(perhaps to 100øE)into the subtropics and is diluted by water from the Indonesian Alongthe Australia-Balisection, the contributionof the three throughflow.At present,the separationbetween AAIW and IIW sources(ST1W, ICW, m-AA1W) showssmall mixing coefficients in this stronglymixed region is not well known. The resultsof (<30%) (Figure8) relativeto the selectedsources (Table 2). The this applicationshow no signal of m-AAIW in the Indonesian hydrologicalfront (at 13ø30'S)marks the limit of the presenceof Straits. theseIndian waters.Seasonal variations are observed,especially for the SubtropicalIndian Water. The STIW is only present 5.3. North Indian Ocean Waters between200 and 300 m in two cores,but the strongerone is at Two sources flow from the Arabian Sea: the Persian Gulf- different latitudes,depending on the season.During the SE monsoon,the ST1W appearsbetween the latitude 17øSand the Arabian Sea Water (at the isopycnal surface of the salinity Australiancoast in weak proportions(10-20%). At the opposite maximum of the Persian Gulf water) and the Arabian Sea-Red season, the core of the ST1W is observed between 14øS and Sea Water. The only source observed in the Australia-Bali 15ø30'S, not deeper than 300 m (<20%). Many physical sectionis AS-RSW (Figure 10), mainly found in the northern processesseem to changesignificantly the characteristicsof this part of the sectionand defined also as North Indian Intermediate source.Quadfasel et al. [1996] showthat the subtropicalflow, Water (NI1W). Its core is centered around 400-600 m (>20%) north of the NW Cape of Australia,splits in two branches,one during the SE monsoonand between250 and 700 m during the part following the shelf break northeastwardand the other NW monsoon,with a slightly higher coefficient (>30%) in the feedingdirectly the SouthEquatorial Current. The first branch core (Figure 7). Fieux et al. [1996a] show that the intermediate couldbring the STIW to the northwestof Australia.It is possible eastward current along the Indonesian coast is stronger in that the branchesmove between the different seasons[Quadfasel February 1992 than in August 1989. However, this could be the et al., 1996]. In the regionoff the NW Cape,there is a relatively result of better sampling near the coast for the SE monsoon. small mean flow with enhancedmesoscale variability [Quadfasel Nevertheless,the most important contribution of this North et al., 1996] and, consequently,the STIW is barely represented Indian IntermediateWater is observedduring the NW monsoon on the Australia-Bali section. This water as well as the other and is corroboratedby the higherproportions during the northern southern sources (ICW and m-AA1W) are absent in the monsoonin the IndonesianStraits (Figure 9). Mixed AS-PGW Indonesian Straits. and AS-RSW is observedalong the Sumatra and Java coasts The Indian Central Water also shows small mixing before reachingthe Indonesianarchipelago (Figure 10). These coefficientsin the Australia-Bali section,appearing inside two waters are flowing from the Arabian Sea to east of the Indian corescentered at 400 m (<30%) at 17ø30'S latitude and at 450 m Ocean. The AS-PGW is characterizedby high salinity and (<20%) at 14ø30'S latitude for the SE monsoon.As for ST1W, oxygenmaxima spreading between 200 and 300 m. The modified the proportionis slightlyweaker in the NW monsoon(<20%) Red Sea water is also characterizedby a salinitymaximum but at (Figure8). In the southernpart of the NW monsoonsection, the a higher density(27.2 < cv0< 27.4) than the AS-PGW. This study geostrophictransports show a successionof reversals,which clearly shows that the water in the Australia-Bali section denotesa large mesoscalevariability [Fieux et al., 1996a]. This originatesfrom the mixing of Red Sea Water and Arabian Sea mixing of the Central Indian Water and the Indonesianwaters Water, with many modificationsoccurring along its path and was alsoobserved by Quadfaselet al. [1996] in the thermocline particularly between Sumatra and Bali through mixing with off the northwestAustralian shelf. In agreementwith the I1W Indonesianseas waters (Figure 10). distributionin this region,the ICW appearsto mix with the I1W when it flows eastwardduring the NW monsoon.The small 6. Biological Tracer Utilization: Comparison proportionsobserved for the ICW and the STIW suggestthat for JADE 1989 thesewaters are subjectto many changesalong their pathways from the anticyclonic subtropicalgyre to the northwest of The seasonalanalysis was performedusing three tracersand Australia.Rochford [1969] showedthat the Indonesianwaters at continuity.Seven sources were definedto explainthe water mass 110øE,between 100 and 150 m, characterizedby low salinityand mix in the eastern Indian Ocean. In order to specify the meanoxygen content, spread southwards (around 26øS at 110øE) contribution of the different water masses to the water mass mix, duringthe NW monsoon(Leeuwin Current). The 0-S diagrams we introducebiological tracers into the multiparametricprogram. from severalsections off NW Australia[Quadfasel et al., 1996] In the easternIndian Ocean, there are young and old water indicate a very strong attenuationof the salinity maximum masses,showing different biological characteristics.Therefore characterizingthe Subtropical Indian Water. Owing to the the nutrients become good tracers of these water masses. mesoscalevariability observedin 1992 [Fieux et al., 1996a], However, because of their nonconservative behavior, the whichcould enhance the mixing of the ST1W and ICW with I1W, biologicalvariation of thesetracers must be takeninto accountby the mixingcoefficients for the southernIndian watersare slightly introducing a biological unknown (see (2)). This unknown higher in 1989. collects togetherthe biological variability in the water mass The modified Antarctic Intermediate Water is present in a throughoutits routein the oceaniccirculation and the variability largerproportion than the two otherSouth Indian sources(Figure in the watercolumn of the JADE stations.It allowsthe studyof 20,816 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

-15 -10 -5 0 5 -1 0 1 2 3 -20 -10 0 10 - - . ++ 0 .... ',..... :";:'-'-I:•',...... -00 i'*_- ..... -100 + + -100 ? ....

-200 -200 +4•+ + -200 + + + -300 -300 -3OO -4oo -4oo -400 -500 - -600 • -600 -600 + -700 -700 -700 +• + -800 + + +4•

-900 -900 -900 + + 444.4.•+ 4+++

+ -000-800 -000-800 -1000

Figure11. Residualsof (left)heat (øC), (middle) salinity, and (right) silicates (!amol kg 'l) forall sectionsof JADE 89.

theratios between the biological unknowns and analysis of their AS-RSW, respectively.These values have been calculatedat evolutionin comparisonwith Redfield ratios. For the seasonal locationswhere the sources penetrate the section with the highest study,the unknown of oxygenwas not used, because with only coefficients. threetracers, the introduction of thisparameter would have been Theresiduals for potentialtemperature, salinity, and dissolved equivalentto a small weight on oxygen.Since there were no silicateare close to zerofor the200-800 m layer(Figure 11). No nutrientdata during JADE 92, the applicationwith the nutrient residualsare observed for oxygenand nutrient tracers (phosphate tracerswas only possible with the JADE 89 data.A comparison andnitrate), because all thevariations are given by thebiological with the resultsobtained with the T, S, and O2 tracersand unknowns(Figure 12). The relationbetween the biological continuitywill be discussedto show the importanceof the unknownsAO2/APO4 shows a slope (around-178), which is introduction of nutrients as tracers of water masses. closerto theratio -175 definedby Takahashiet al. [1985]than to 6.1. Uncertainties,Residuals, and BiologicalUnknowns the Redfield ratio -138/1 [Redfield, 1958]. An the relation betweennitrate and oxygen,the slopeAO2/ANO3 (• -7) is An analysis of the standard deviations shows that the slightlylower than the Redfieldratio (-138/16 •, -8.625) coefficientsmust be takenwith the followingaccuracy: during [Redfield,1958]. The analysisof the data set showsthat the few theSE monsoon, in theAustralia-Bali section, the uncertainty of remotepoints, with a low valueof ANO3 anda highvalue of AO2 the coefficientsis 0.2%, 4.2%, 3.8%, 0.5%, 0.5%, and 5.8% for (Figure 12), correspondto the sectionnear the equatorand STIW, ICW, m-AAIIW,ISW, IIW, andAS-RSW, respectively. Sumatra. The low valuesof ANO3 are observedin the water For the equator-Sumatra-Javasections, the uncertaintiesare massescoming from the Arabian Sea. The water massesformed 0.8%, 0.85%,2%, and4.8% for m-AAIIW, IIW, AS-PGW,and in the NorthIndian Ocean are subjectto intensebiological a) APO4(#mol kg'•) b) ANO3(#mol kg'•) c) APO4(#mol kg'•) 0 0.5 1 0 5 10 15 20 0 0.2 0.4 0.6 0.8

. • -40 o o

-60 -60 . -80 -, • 6 -100 ', 4•o oø

-120 -120 0

Figure12. Relationbetween the parameters ofbiological variation for all sections ofJADE 89. Squares represent theBali-Australia Straits sections, and circles represent the equator-Sumatra-Java sections. Comparisons with the Redfieldratio (dashed line) are -O2/P, - 138/1; -O2/N, - 138/16; and N/P, 16/1. (a) zXO2=- 178.40zXPO,• - 2.40 (number of samplesn=310, correlation coefficient r=-0,834); (b) zXO2=-6.92ANO3+ 34.05 (n=303, r=-0.334); and (c) zXNO3=25,76APO,•(n=308, r=-0.221). COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW 20,817 activity. Large oxygendepletion is seenin the Arabian Sea at 200 [1996b]) and, consequently,poor in nutrientsand rich in oxygen. m [Mc Gill, 1973]. In this zone of the Arabian Sea, The biological activity in those water massesis less important. denitrificationand nitrogen fixation modify the nitrogen pool, The water massescoming from the Indonesian seas are rich in and therefore the ratios between the biological elements are dissolvedsilicate, and thosecoming from the North Indian Ocean different from the Redfield ratios generally observed in the have undergoneintense biological activity. This variability in the ocean. Low N/P ratios are expected in regions of strong biological characteristicsallows us to better separatethe sources denitrification in the water column. If we do not take into account and, consequently,give supplementaryinformation about the thesedistant points, the distributionof the points showsa slope water masses. close to the N/P Redfield ratio. The ratio ANO3/APO4(• 26) 6.2. Water Masses observedfrom the JADE data (Figure 12) is higher than the ratio 16/1 defined by Redfield [1958] becauseof the high values of The distributionof the water massesis presentedin Figures ANO3 that deviate from the general distribution. These high 14, 15, 16, 17, and 18. Some quantitativedifferences are shown valuesare also found on the equatorsection. The distributionof in comparisonwith the analysisusing the T, S, and 02 tracers. these unknowns in the Bali-Australia section and Indonesian These differencesare observedfor the Indian waters,especially Straits(Plate 1) is in agreementwith biologicalprocesses in the for the North Indian Ocean sources and the modified Antarctic water masses.Small AO2 values are observedsouth of the front, Intermediate Water. wherethe SouthernIndian Water is located.Large ,502 valuesare 6.2.1. Indonesian waters. The Indonesian waters show the observednorth of the front, where waters coming from the samespatial distribution (Figures 14 and 15), with slightlylower Indonesian seas and the North Indian Ocean are present. mixing coefficientsfor the I1W (<60% above 500 m, north of Althoughthe biologicalunknowns should contain information on 13ø30'S) in agreementwith Rochford [1963]. In the Indonesian both local and remoteexport production through remineralization Straits (Figures9 and 15), the contributionof I1W is less marked processeswithin the wate,rmasses, their spatialdistribution also for depthsshallower than 500 m. reflectspart of the long-term (annual and large scale) primary 6.2.2. South Indian waters. The STIW is representedby a productionin the investigatedarea. Such analysisis presentedin low mixing coefficient(Figures 8 and 14). In comparisonwith Figure 13, where the resultsof ,502, ,5NO3, and ,5PO4have been the results obtained with the three tracers, there is a slight averagedover the depth range 200-800 m. These results are differencein its distributioninside one core (Figure 8). The ICW comparedto the large-scaleprimary production fields calculated is present inside two cores (>20%) centered around 400 m at by Antoine et al. [1996] using the coastal zone color scanner 17ø30'S and 450 m at 14ø50'S (Figure 13), at the samelatitudes (CZCS) climatologyof chl a. The distributionof annualprimary and depthspointed out in the analysiswithout nutrients(Figure production derived from remote sensing observation and 8) but with slightly higher coefficientsfor the core at 17ø30'S. extracted along the JADE track (Australia-Bali, Figure 13) Two coresappear in the m-AA1W distribution.They are centered presentslarge values in the northof the section,a "plateau"in the around 450-500 m, similar to the distribution obtained from the frontal area (12øS-14øS),and a minimum at around 17øS.Near hydrologicalmultiparametric analysis. The m-AA1W appears the coastof Australia, we also note a slight increasein primary slightlybelow the ICW. Thesedepths (450-500 m) correspondto production.The biologicalunknowns for oxygenand nutrientsdo c•0=26.8-27.0. Rochford [1963], using a salinity frequency not follow perfectlythis distribution.However, there is a trend of analysis, shows that the AA1W spreads between Bali and high valuesin the north and low valuesin the southof the section Australiaat c•0=27.00.He alsoshows, at c•0=26.90,the presence (note the inverseaxes for oxygen),indicating that the biological of the AA1W along both sidesof Timor and at c•0=27.00,west of unknowns captured regional memory of biological activity. Timor. In the IndonesianStraits section (Figure 15), the m- Differencesbetween the two fields, such as the high values in AAIW is also found west of Timor but between 250 and 500 m ,5PO4 at 13øS, may be related to the "instantaneous"picture and mainly centeredat 300 m aroundc•0=26.60, which is quite obtainedwith the JADE 89 data comparedto averageestimation different. There is no indication of a connection between the of primaryproduction calculated with compositefields of 8 years Timor Sea and the west Australian coast. Rochford [1963] of satellite imagery including the interpolationprocedure. In suggeststhat, at temperaturesand salinities higher than the addition,the biological unknowns are associatednot only to local minimumsalinity, the characteristicsof the AA1W mergeinto the informationin exportproduction (vertical sedimentation) but also characteristics of the Indonesian waters. Both the Antarctic and to advective transport (horizontal) of remineralized material Indonesian Intermediate Waters are identified by a salinity produced in remote surface layers. For example, the high minimum, and their identificationbecomes very difficult with variability in the north and peaks in ,502 and APO4 observedat only hydrologicaltracers. In the sameway, the hydrologicaland 13øSare certainlyrelated to significantinput of materialfrom biological characteristicsof the ISW (Table 2) can becomeclose Indonesianwaters, a signalcoherent with geostrophictransport. to thoseof m-AA1W at intermediatedepths. Consequently, it is In moredetail, it is interestingto find a high ,5PO4signal around possiblethat the presenceof m-AA1W in the IndonesianStraits 300 m betweenstations 9 and 10 (Plate 1 and Figure 13), at the results from an incomplete separationbetween m-AAIW and samepair of stationswhere a westwardsubsurface current of 20 ISW. An earlier study [Fine, 1993] suggeststhat the AAIW cm s-1 around 200 m hasbeen calculated [Fieux et al., 1996a]. appears to spread both north and northeastward into the On the otherhand, the reasonwhy this signalis apparentin APO4 subtropics.There, the propertiesof recently ventilated AAIW and`502 distributionbut not in ,5NO3remains an openquestion. appearto be diluted by water from the Indonesianthroughflow. In the Indonesian Straits (Plate 1), nutrient and oxygen On the sectionsoccupied at the equatorand off Sumatraand Java unknownsare large at depthsof 350-400 m. The characteristics (Figure 16), the AA1W is also found around 400 m (mixing of the sources from the Indonesian seas and the South Indian coefficientabout 20%). However, Wyrtki [1961, 1971] showsa Ocean are different from those of the North Indian Ocean. On the salinityminimum at c•0=27.4(depth around 700 m) near Sumatra section,the sourcesoriginating from the South Indian Ocean are asthe lasttrace of the AntarcticIntermediate Water sinkingalong younger water masses (see CFC distribution of Fieux et al. the AntarcticPolar Front. With the multiparametricanalysis on 20,818 COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW

Primary Production (2oo.8oom) (#molkg '1)

(gCm'Eyr -1) -: 5

300

250

200

150

100 [ , t , I , I ,

-8 -10 -12 -14 -16 -18 -20 -10 -12 -14 -16 -18 -20

Latitude (øS) Latitude (øS)

(2oo.8oom) (#molkg q) (2oo.8oom) (#molkg 4)

0.16

0.12

0.08

0.04

-8 -10 -12 -14 -16 -18 -20 -8 -10 -12 -14 -16 -18 -20 Latitude (øS) Latitude (øS) Figure13. Comparisonbetween primary production (gC m-2 yr -•) andthe average of thebiological unknowns (,502,APO4, and 'ANO3) (•mol kg-•) in the200-800 m layerfor theAustralia-Bali section. Values of primary productionhave been calculatedfrom satellitedata.

the three tracers and continuity, m-AAIW and IIW are not The analysis of the mixing coefficients shows that AS-RSW meaningfully representedon the sectionsbetween the equator coefficientsare high below 800 m along Sumatra.However, all and Java. residualvalues increasebelow this depth, suggestingthat these 6.2.3. North Indian Ocean waters. High nutrient coefficients may not be meaningful. Nevertheless, this concentrationsand low oxygen content characterizethe North observationis corroboratedby the definition of the core layer of Indian waters. These characteristics are due to important RSW by Wyrtki [1971]. Consequently,the introductionof the biological activity in the Arabian Sea and from the effectsof the nutrientsinto the multiparametricsystem further constrainsthe upwelling producing living matter requiring oxygen [Wyrtki, system.The results are in good agreementwith data published 1971]. Along the sectionsfrom the equatorto the straits,we can earlier [ Wyrtki, 1971; Fieux et al., 1994, 1996a, b]. observethe spreadingof thesewater masses(Figures 17 and 18) during the SE monsoon.The AS-PGW is observedbetween 200 7. Conclusions and 600 m (<25%), and AS-RSW is presentbelow 550 m (>25%) in the Equator section. Along its path to the Australia-Bali In this paper,we have presenteda new way of looking at the section,the proportionsof the AS-PGW decreaserapidly and are JADE data. The resultsof the multiparametricanalysis, between not observed near Bali (Figure 18). Its composition is 200 and 800 m, are in good agreementwith the present significantly modified between the sections situated south of knowledge of the water mass circulation in the Indonesian Sumatraand west of Java. These changesin the distributioncan throughflow.Using two seasonalhydrographic data setsfrom the come from the influence of the outflow of the Indonesian Sea JADE cruises,the estimatedproportions of mixing of the water Water (Figure 16), which can be followed along Java and massesshow seasonalvariations, particularly for the northernand Sumatrafrom the high silicatevalues. This differenceis relatively southern Indian Ocean waters. During the SE monsoon, the small in the AS-RSW distribution.It showsa spreadingclose to South Indian Oceanwaters (ST1W, ICW, and m-AAIW) appear the Indonesian coastsbelow 400 m (>20%). A core of the AS- south of the hydrologicalfront by intrusionfrom the northwest RSW (>35%) is also observedaround 700-800 m at the equator. Australiaregion, with proportionsslightly increasing with depth. COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW 20,819

STIW Jade 1989 ISW Jade 1989

2 3 4 5 6 7 $ 9 10 I1 12 1314151617 19 2 3 4 5 6 7 $ 9 10 11 12 1314 i51617 19 -2OO -200, • 0.5 • o -300 -300-i•: •0.1 %•o.:• ß•o.• -400 .1 • ß -5OO - 0t + + + * + + + + + ß +

+ -600 ß • ;2-600 0.1•

+ + -700 ß '? -700 ß + + . + + + + + . . + +

I

Latitude (oS) Latitude (øS) CIW Jade 1989 IIW Jade 1989

2 3 4 5 6 7 $ 9 10 II 12 131-1,lS 1617 19 2 3 .l 5 6 7 $ 9 10 11 12 1314 15 1617 l0 -200 ...... ' -200 i ,/ , t , i , i ßß '0.2' ' • -300 ...... • -300 -400 • -400 -500 '; •-500

-600 • •2 -600

-700 ß - -700

-8OO ß ,' -' ,.... ,' ,', -800 . - • . i ß , . i ß , - , ß • ß , ß , -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude (øS) Latitude (øS) m-AAIW Jade 1989 AS-RSW Jade 1989

2 3 4 5 6 ? $ 9 10 11 12 1314151617 19 -200 -300 ]•.•,...... o.! ]..-?.' ß ß ß Ii' -300-200 -400 0.;2 . . • -500 ß I •-500

-600 .0.2 +0• ß • • -600

-700 • -700

-8OO ,' . ', .... ß .' ,.... ,' . ',• -800 [ ,k, ,, ,. [ . [, . ,[ . ] t ,, ., 1, d.. , ,, . , ! -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 Latitude (øS) Latitude (øS) Figure 14. Mixing coefficientsof the Indonesianand South and North Indianwater masses in the Australia-Bali sectionfor JADE 89 (with the multiparametricsystem using nutrients).

Near the Bali coast,only AS-RSW is presentwith smallmixing 13ø30'S and 10ø30'S for the subsurfacewater. The IIW is proportions.The AS-PGWflows from the ArabianSea along the presentbelow 500 m over the whole sectionfrom Bali to Sumatra coast and vanishessouth of the Sumatra Island. The Australia.During the NW monsoon,the contributionof the three Indonesian waters have high mixing proportionsbetween sourcesfrom the SouthIndian Ocean is relativelyless important. 20,820 COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

STF• Jade 1989 ISW Jade 1989 38 39 3•3!•$ 38 39 23 22 21 20 23 22 21 20 -2OO 3?35344•7 26 25 363534 4•)2726 25 .. -200o•ß '__L-•---'-. .•-. 8.I-' o.,o.: ).4 ----- 0.4 ---- b-4____ 0.4 ß . + .. **+ , ß -300 + -300• •- '__5_ 0.3o___.0.3'-_:- 0.: ).3 ß 0.3..• -400 -400 • 6.2--•0.2 • 0.: 9'2• . -500

o.1 ).1---- 0.1 -600 -600 . -• .-77'..o.•.--•o.• .

+ -500!i "+ +* "+ + *

+ -700 -700 -' ß

+ -800 -800 ß -io -io Latitude (øS) Latitude (øS) CIW Jade 1989 IIW Jade 1989 38 39 3•3!•$ 38 39 32•3•$ 363534 4•2726 25 23 2221 20 363534 4•:/2726 25 23 22 2l 20 -2OO -200 • o.•'•. - 0.3- - o.- k•0.4-----'y -300 ).5 •

-400 + -300-[•__•o.40.5 .....0.5 • 0' -400•,d-' o6C•--. ß ß '- f- '• -o• -500 0.7..•.•..0 7 --.-rr-..•.•• ' }.6• 0.6'• + -soo ).7•' 0.7----' -600 -600]...0..x'b.a-'o.8 15.8 ß .. 0.9--w- 0.9 ----- 0.9 • "0.9 -700 -700 -' - ).9 -- 0.9 ----

.. -800 I -800 - -il -io Latitude (øS) Latitude (oS) m-AAFW Jade 1989 AS-RSW Jade 1989 38 39 3•25 38 39 32•3•$ 23 22 2l 20 20 -2OO 363534 4•92726 25 -200 363534 4.•2726 25 23 22 •.1 .__..,• . 0.2 • -300 ...... •z._ 6.2_{ -300 -400 -400 -500 -500

+

-600 -600 + +.. +

+ -700 -700 +

-800 , , ' .' , -800 ß , , -11 -10 -9 -11 -10 Latitude(øS) Latitude(øS) Figure 15. Mixing coefficientsof the Indonesianand South and North Indian water massesin the Indonesian Straitssection for JADE89 (withthe multiparametric system using nutrients ).

Their coresof distributionshow variations, particularly for the practicallymissing below 200 m. Near the Bali coast,the AS- ICW. Thesevariations are due to strongmesoscale variability in RSW appearswith slightlyhigher mixing proportionsand is the southernpart of the Bali-Australiasection, also shownby further observed in the northern Indonesian Strait. The Bray et al. [1997]. Duringthe NW monsoon,the STIW is Indonesian waters show similar distributions in the two seasons. COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW 20,821

ANO3Bali-Australia Jade 1989 •qO3Str•ts Jade 1989

2 3 4 5 6 7 $ 9 10 II 12 1314151617 19

-300 ' "' 's ...... 6-' -3O0 6 -400 ...... '"• -400 [ . . 6 ., .- ...... -500--- 6 -'' ' - . -600/, s ..6. . 6 ß . . 6 ...... • - . -700 .

-8O0 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -11 -lO -9 Latitude('S) Latitude(øS) APO4Bali-AustraliaJade 1989 APO4Straits Jade 1989 2 3 4 S 6 7 8 9 I0 II 12 1314151617 -2003635 3•-- -•J • 25 • = • 20 o! -300 ...... ß ß o , i o. 15 -4O0 ! . ,.,. o.•5ß ß ß o.'" ß'--ß ß •--' -500-400 i -''Is ...... o,t . . . o 0.05 ß o + o. . . •-600-- ß "f .1 -700 .,. , J.J. -800 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -11 -10 -9 Latitude (øS) Latitude (øS) AO2Bali-AustraliaJade 1989 AO2Straits Jade 1989 38 39 3•(•28 2 3 4 5 6 7 8 9 10 11 12 1314151617 19 -200 •j •6_. -5-10 -15.IO - o -15 -o ' • -o - .-5 -0 • -400 ...... ' '•' ' d5 -500. '-- -.•.• - 2• . -5 -$ ' - o . olo • -600 ..... ' -•o ß -i0'--• '- . • -600.- .s . . -5 -I0 -7• ß ' -s .... -5 .... 700 -5

-18-17 -16 -15 -i4•'"13 -12 -11 -10 -9 -11 -io -9 Latitude (øS) Latitude (øS)

Plate 1. Distributionof the biologicalvariation parameters (AO2, APO4,and ANO3) in the Australia-Balisection in the Indonesian Straits for JADE 89. 20,822 COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

m-AAIW Equator IIW Equator

62 61 60 62 61 -200 -200 <.-0.2 ------0.2 • 0.2- -3OO 0.2 ' -3OO

,• -400 -400 0.1/ .z -500 0.2 '0.2- -500 --'0.2 ' 0.2 ' ch -600 -600 ' . • • 0.3 0.'3

-700 -700 --0.4 o -800 -800 96 9'7 98 96 97 98 Longitude(øE) Longitude(øE) m-AAIW Sumatra 1 IIW Sumatra 1

55 54 53 52 50 49 48 55 54 53 52 50 49 48 -200""•'• •'• 0.2 -200 -30012• 0.2ß -3OO -400 0.•. 2 ' -400 .•------•.•o.2 -500 •/// 0. .0.4'3(•) 0.3ß ß _,002/o. 0.2• -600 .... -600

-700 ß -700

-800 -800 99 100 101 102 103 104 99 100 101 102 103 104 Longitude(øE) Longitude('E) m-AAIW Java I• Java

41 42 43 44 45 46 4'/ -200 ' ' -200

-300 ß . o . -3OO -400 -400 . -500 -500

-600 -600

-700

-700-800 , . -800 -9 -• ' -• ' -6 Latitude (øS) Latitude (øS)

Figure 16. Mixing coefficientsof the m-AA1W and I1W in the equator,Sumatra, and Javasections for JADE 89 (with the multiparametricsystem using nutrients).

The mixing coefficients (in relation to the defined sources) act upon the typical magnitudeof the throughflow [Meyers, allowed us to show that the Indian Ocean water masses are 1996]. Thereforethe data analyzedfor the seasonalstudy might subjectto strongmixing off NW Australiaas well as north of the be subject to the likely interannualeffects resulting from the Indian Ocean before reaching the input from the Indonesian climatic context of the JADE cruises. archipelago.Moreover, they show that the monsoon system The resultsof the inversionusing the nutrientsdo not show generatesseasonal variability of the water massdistribution with, important changesin the general structure of the water mass notably,a slightlygreater presence of North Indian Oceanwaters distribution.Supplementary information in the mixing analysis during the NW monsoonand South Indian Oceanwaters during can be obtained for several water masses such as m-AAIW the SE monsoon.Other variations,principally interannual, also observedinside the IndonesianStraits. However, as suggestedby play a role in the distributionof the water masses.The JADE Rochford [ 1963], the characteristicsof m-AAIW and Indonesian cruiseswere performedin 1989, at the end of a La Nifia phase waters are very close in the studiedregion. Consequently,the (leading to an increaseof rainfall in the region) and in 1992 distributionof m-AAIW at shallow depth can result from an during an episodeof E1 Nifio (decreasingrainfall in the Indo- incomplete separationbetween m-AAIW, ISW, and IIW. The Pacific region) [Fieux et al., 1996a,b]. Theseclimatic events also separationbetween the AS-PGW and AS-RSW distributionsis COATANOAN ET AL.' WATER MASS DISTRIBUTION IN THROUGHFLOW 20,823

AS-PGW Equator AS-RSW Equator

62 61 60 62 6l 60 -200 . -200 - ./ 0.2 -300 -300 /,-- . 0.'2 • 0.2 •o.q• s --0.1 -400 ..•=;>0. }.15 J 0.2 E -400 • 0.2 -- . -500 o _c: -500 -.0.2• ß ' 0.2• - 0.25• 0.25 -600 0.2 •-•- 0.2 C2 -600 -0.3 -0.15 -700 0.15 -700 - 0.35 0.35 -8OO -8OO 96 98 96 97 98 Longitude(øE) Longitude (øE) AS-PGW Sumatra 1 AS-RSW Sumatra 1

55 54 53 52 50 4q 48 55 54 53 52 50 49 48 -200 ...... -200 o.-•'•-o.• .... _o.1 o.1• -300 -300 • •'o.•s• . •' -400 '•' 0. 015 0.15. .[ •_400 -500 "- -500 .1 .) 0'.2 • -600 ß • -6oo

-700 -700

-800 -8OO 99 100 101 102 103 104 99 lOO 1Ol 1o2 103 104 Longitude(øE) Longitude(øE) AS-PGW Java AS-RSW Java

43 4• 45 46 4'7, .a5 46 4'/ -200 -200

-300 ß -30O

•- -400 /j 0.2• 0.2 -400ß • o. 15 • • 0.2------500 • -500 0.25

-600 • -600 ß o .•75 ' •'• 625 <"--•

-700 -700

-800 -8OO -9 -8 -7 -6 -9 -8 -7 -6 Latitude (øS) Latitude (øS) Figure 17. Mixing coefficientsof the North Indian water massesin the equator,Sumatra, and Java sectionsfor JADE 89 (with the multiparametricsystem using nutrients). well representedalong Sumatra and Java. Lower mixing This study confirmsthe usefulnessof nutrientsas water mass coefficientsof AS-RSW can be explainedby the presenceof IIW tracers. The introduction of biological parametersmakes it along Java and Sumatraconstrained by silicate.The AS-RSW is possibleto separatethe variationsin nutrientsfrom biological also observedat deeperlevels along theseislands, in agreement activity on one hand and from dynamics on the other hand. with the definitionof this corelayer by Wyrtki [ 1971]. Future analysiswill allow the separationof changesin nutrients 20,824 COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW

95øE 100øE 105øE 110øE 115øE 120•'E 125øE 5øN 5•N

0':',....•O..- • •, 0 ø 0.2

o

ß Sea :. 5 øS 5øS[ '0.•W--x• ' i ß 10øSI ! .

• Indian Ocean . 15øS 15øS'iAS-PGWSigma0 =26.5 -; 20øS...... i ...... (around ...... ::.... 300 ..:,•...::.:...... m) ...... ' A_ [:i• 20øS 95øE 100øE 105•E 110øE 115øE 120øE 125øE

95øE 100"E 105•E 110"E 115øE 120•'E 125•E 5øN ,• 5øN

I . ' ...•oi•. %".C.... 0øs

(around 5 O0 ) 2()øS '--- ...... 5 20øS 95øE 100øE 105øE 110øE 115øE 120øE 125øE

Figure 18. Isopycnaldistribution of the mixing coefficientsof the North Indian water massesfor JADE 89 (with the multiparametricsystem using nutrients).

from local biologicalactivity as well as biologicalactivity along References the path of the water mass. Such analysiswill allow greater Antoine,D., J. M. Andr& and A. Morel, Oceanicprimary production, 2, understandingof the changesin the biogeochemicalcycle in Estimationat global scalefrom satellite(coastal zone color scanner) responseto oceaniccirculation. chlorophyll,Global Biogeochem.Cycles, 10, 57-69, 1996. Bolin, B., A. Bj6rkstr6m, K. Holman, and B. Moore, The simultaneous Acknowledgments.The supportof the IFRTP, INSU-CNRS, and the use of tracers for oceans circulation studies, Tellus, Ser. B, 35, 206- FrenchEmbassy in Jakarta,together with the supportof the Indonesian 236, 1983. BPPT and the PuslitbangOsealonogi LIPI, are greatlyacknowledged. We Bray, N. A., S. Hautala, J. Chong,and J. Pariwono,Large-scale sea level, thank A.G. Ilahudefor his helpfulcollaboration. We thank all the persons thermocline, and wind variations in the Indonesian throughflow who participatedin the collectionof the hydrologicaldata and madethe region,J. Geophys.Res., 101, 12,239-12,254, 1996. measurementsof salinity,oxygen, and nutrients during the two cruises. Bray, N. A., S. E. Wijffels, J. C. Chong, M. Fieux, S. Hautala, G. COATANOAN ET AL.: WATER MASS DISTRIBUTION IN THROUGHFLOW 20,825

Meyers, and W. M. L. Morawitz, Characteristicsof the Indo-Pacific Metzl, N., B. Moore, and A. Poisson,Resolving the intermediateand throughflowin the easternIndian Ocean, Geophys. Res. Lett., 24, deep advective flows in the Indian Ocean by using temperature, 2569-2572, 1997. salinity,oxygen and phosphatedata; the interplayof biogeochemical Broecker, W. S., W. C. Patzert, J. R. Toggweiler, and M. Stuiver, and geophysicaltracers, Palaeogeogr. Palaeoclimatol. Palaeoecol., Hydrography,chemistry and radioisotopesin the southeastAsian 89, 81-111, 1990. basins,J. Geophys.Res., 91, 14,345-14,354, 1986. Meyers, G., Va.riation of Indonesianthroughflow and the E1 Nino - Chiswell, S. M., K. A. Donohue, and M. Wimbush, Variability in the SouthernOscillation, J. Geophys.Res., 101, 12,255-12,263, 1996. centralequatorial Pacific, 1985-1989. J. Geophys.Res., 100, 15,849- Miyama, T., T. Awaji, K. Akitomo, and N. Imasato, Study of seasonal 15,863, 1995. transportvariations in the Indonesianseas, J. 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M. Fieux, Laboratoire d'Oc6anographie Dynamique et de Climatologie,CNRS/ORSTOM/UPMC, Universit6Paris 6, Case 100, 4 PlaceJussieu, 75252 ParisCedex 05, France.(mf@ lodyc.jussieu.fr) C. Coatanoan,Department of Marine Chemistry and Geochemistry, N. Metzl, Laboratoirede Physiqueet Chimie Marines, INSU/CNRS, Woods Hole OceanographicInstitution, 360 Woods Hole Road, MS 25, Universit6 Parris6, Case 134, 4 Place Jussieu, 75252 Paris Cedex 05, Woods Hole, MA 02543. ([email protected]) France.(metzl@ ccr.jussieu.fr) B. Coste, Laboratoire d'Oc•anographie et de Biog•ochimie, CNRS, Centre d'Oc•anologie de Marseille, Case 901, 163 Avenue de Luminy, (ReceivedMay 27, 1998; revisedMarch 22, 1999; 13288 Marseille Cedex 09, France. ([email protected]) acceptedMarch 24, 1999.)