Nutrients in the Indian Ocean

M. Dileep KumarNational Institute of Oceanography

Dona Paula, Goa, India

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Nitrogen, phosphorus & silicateTrace metals

• Distribution• Processes• Driving forces

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Monsoon circulationPrimary ProductionNutrients – Nitrogen biogeochemistry

Distance (km)

Dep

th (m

)D

epth

(m)

Meridional variability in nutrients – geographic domains

Monsoon GyreSouthernSubtropicalGyre

Polar

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Zonal variability in nutrients

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Monsoons as driving force

Monsoon forcing: North Indian Ocean

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River discharges & differential vertical mixing

INDIANSUBCONTINENT

Bay ofBengal

ArabianSea

1.6x1012 m3/yWATER 0.3x1012 m3/y

1.4x109 tons/ySPM 0.2x109 tons/y

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Primary Productivity map

Global Primary production Behrenfeld and Falkowski (1997)

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Nitrate deficits, global significance of del N and N2O fluxes

Del N = 1/3 Global? N2O flux = ~8% Global

N2OO2

NO3

NO2

19oN, 67oE

N*Gruber &Sarmiento (2002)

NO3 DeficitCodispoti et al. (2001)

from Naqvi (2006)

Excess N2

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Decoupled active denitrification region

Naqvi (1991)SIBER

-O2: C: N: P Reference

138:106:16:1 Redfield et al (1963)

126:96:15:1 Sen Gupta & Naqvi (1984)172:119:14.9:1 Takahashi et al (1985)118:125:14.2:1 O2>10 μM; Millero et al (1998)145:42:6.3:1 O2<10 μM; Millero et al (1998)139:90:14.4:1 550-1200 m; Hupe & Karstensen (2000)152:107:14.9:1 1200-2000 m; Hupe & Karstensen (2000)Denitrification

130:94:10.3:1 (θ < 12oC) EQIO; Li & Peng (2002)Partial conversion of organic nitrogen to ………..

Redfield ratios – anomalies

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Bange et al (2005)

Implications to mineral formation

Redfield ratios – phosphate accumulation in O2 deficient waters

Samples collected from < 200 m

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Nitrate deficits in the East Indian Ocean ?

Kumar (2001)

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Broecker et al. (1980)

Kumar & Li (1996)

North suppliesmaterials to theSouth Indian Ocean

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How much do we know about forcings?

Inputs to North Indian Ocean (Naqvi, 2006)

River & groundwater 0.56Atmospheric deposition – trace metals 2.9Fixation 3.8Sedimentary fluxes ???Exchanges with marginal seas 0.7Vertical mixing – upwelling ???

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Evaluation of nutrient supplies – rivers

1950 1960 1970 1980 1990 2000Year

0

4

8

12

N -

Fert

ilize

r use

d (1

06 ton

s)

0.8

1.2

1.6

2

2.4

2.8

3.2

Mar

ine

Fish

Cat

ch (1

06 ton

s)

Seitzinger et al. (2002)

Naqvi et al. (2000)

Kumar (2004)

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No reliable dataavailable for realistic estimates

Goes et al. (2005) SIBER

Evaluation of nutrient supplies –Upwelling ……Eurasian Snow Cover !!!

We have reasonable knowledge ondistributions….

BUT …….. very little on the• variability in abundances • quantitative nutrient transfers and

transformations

We NEED to have integrated time-seriesmeasurement systems strategically placed(Process expeditions-moorings-satellites)

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Thank You!

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