Inorganic Carbon Distributions and Air-Sea CO2Exchange in the Indian Ocean

C.L. Sabine, R.A. Feely, N. Bates, N. Metzl, R.M. Key, F.J. Millero, C. LoMonaco and C. Goyet

Gas Exchange

Ocean Physics Biology TAlkTAlk

pCO2pCO2

TCO2TCO2

pHpH

Take home message:Each of the 4 measurable carbon parameters can tell us something different about the basic processes operating in the Indian Ocean

North Atlantic has the largest column inventories

of anthropogenic CO2(mol m-2).

The Most Comprehensive Look at Carbon Distributions Occurred in the 1990s as part of the WOCE/JGOFS/OACES Global Survey.

Global Inventory of Anthropogenic CO2:

118±19 PgC

More than 60 cruises with approximately 72,000 pairs of carbon measurements

GLODAP synthesis is publicly available from CDIAC (NDP 083)

http://cdiac.esd.ornl.gov/

Gas Exchange

Ocean Physics Biology TAlkTAlk

pCO2pCO2

TCO2TCO2

pHpH

Rising CO2Levels

Changing Climate

Changing Biology?

Question for SIBER:How will ocean carbon system respond to changes in ocean processes?

Total Alkalinity: Surface Talk Distribution is Very Similar to Salinity

Shallow Indian Ocean Data (depth < 100 m)

Potential Alkalinity in Bottom Waters Follows Water Mass Age

Potential Alkalinity = (Alkalinity + Nitrate) / Salinity * 35 ala Brewer et al., 1972

Global Carbonate BudgetFlux term mmol CaCO3 m-2d-1 Gt PIC yr-1 Production or calcification 0.3 – 1.5 0.5 – 2.4 in the euphotic zone Export from surface (models) 0.3 – 1.1 0.4 – 1.8 Export from surface (traps, Pacific) 0.9 – 3.0 1.4 – 4.7 Dissolution in upper 1500 m Atlantic 0.3 0.1 Pacific 0.8 0.6 Indian 1.1 0.3 Total 1.0 Export to traps below 2000 m 0.38 ± 0.24 0.6 ± 0.3 Dissolution on sea floor below 0.24 ± 0.17 0.4 ± 0.3 2000 m (Atlantic and Pacific) Burial in Holocene sediments 0.08 0.1

Berelson et al., 2006

Indian Ocean TA*: A Measure of CaCO3

Dissolution

Anthropogenic CO2is causing carbonate saturation horizons to shoal in all oceans

TCO2: Surface Distribution is Similar to Nutrient Distributions

Shallow Indian Ocean Data (depth < 100 m)

Net Community Production Based on TCO2 Distributions

787

Annual C mass balance

Annual Cmass balance

Monthly C variations suggest Northern IO is net autotrophic

during NEM and SI and net heterotrophic during SWM and FI

From Bates et al.GBC, GB3021, 2006

Revelle Factor

ΔDIC for a 10 ppm change in pCO2 as a function of Revelle Factor

Lower latitudes are more efficient at taking up atmospheric CO2

High Latitudes

Low Latitudes(ΔpCO2/ΔTCO2)/(pCO2/ TCO2)

Zonal inventories of Anthropogenic CO2

The uptake and storage of anthropogenic CO2 in

the Indian Ocean appears to be consistent

with its size, but how might this change over

time?

Preliminary results suggest that North Atlantic accumulation rate over the last decade may have been about half of the North Pacific

accumulation rate.

Water columnAccumulation~ 1.1 mol/m2/yr

Water columnAccumulation~ .6 mol/m2/yr

SurfaceAccumulation

1.3 µmol/kg/yr

SurfaceAccumulation

0.7 µmol/kg/yr

As the US repeat hydrography program moves into the Indian Ocean in 2007-2008 we must ask how ocean carbon uptake is evolving in this region

26,70

26,75

26,80

26,85

26,90

26,95

27,00

27,05

27,10

2100 2120 2140 2160DIC (µmol/kg)

dens

ity

indigooiso

40°S

26,70

26,75

26,80

26,85

26,90

26,95

27,00

27,05

27,10

0 20 40 60Cant (µmol/kg)

dens

ity

indigooiso

2000

19851985 2000

+7 µmol kg-1

+14 µmol kg-1

(Lo Monaco and Metzl, 2005)

Global Net CO2 Flux from Takahashi et al., 2002

pCO2 and sea-air CO2 flux

CO2 Seasonality: large variations in all regions

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300

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380

400

-65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15

Latitude

fCO

2 (µ

atm

)

Wat Jan 2000Wat Aug 2000Air Jan 2000Air Aug 2000

Ice

Summer Sink

Summer SourceWinter Source

Winter Sink

Metzl et al., 2001, 2006

Surface pCO2 Patterns based on WOCE/JGOFS CruisesSurface waters can be fit with empirical functions to +/- 9 ppm

North of 15S is source of ~0.15 PgC/yr while 15S-50S is net sink of ~0.7PgC/yr

(μatm)

Surface water pCO2variability controlled by interplay of thermal and biological effects, but wind speed variability also influences CO2fluxes.

We know that seasonal variability is quite large, but what is the inter-annual variability?

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300

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360

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400

420

-2 3 8 13 18 23 28

SST (°C)

fCO

2 (µ

atm

)

oiso1oiso2oiso3oiso4oiso5oiso6oiso8oiso9oiso11oiso12

Interannual variability 1998-2005: large in austral summer,including in warm waters of the subtropical Indian Ocean

(based on 10 OISO cruises conducted in both summer and winter)

austral winter

austral summer

Metzl, unpub.

Concept: Use Multiple Platforms to Produce Seasonal CO2 Flux Maps

In situ samplingpCO2, SST, SSS

Remote sensing SST, color & windSoon SSS

Algorithm development

pCO2= f(SST, color)

Co-located satellite data

Regional satellite SST & color data

Apply algorithm toregional SST& color fields to obtain seasonal pCO2maps

Algorithm development Gas transfer, k =f (U10,SST)

Wind data

pCO2 maps

Flux maps

Flux = k s ∆pCO2

Generating a Global Seasonal Flux Map

Approach: 1. Improving regional relationships by incorporating additional parameters (e.g. mixed layer depth, chlorophyll)

2. Improving regional relationships using ship-based and moored pCO2sw observations

Based on NCEP II winds and SST

Goal: Reduce average regional uncertainty in CO2 flux to <0.2 PgC yr-1

Surface pH distribution reflects combined patterns of alkalinity and TCO2

pH Minimum Associated With O2 Minimum –shallow in Northern Indian Ocean

As long as CO2 continues to enter the ocean, pH will

continue to drop

The changing pH is important because it highlights a changing chemical speciation in

the oceanCaldeira and Wickett, Nature, 2003

After Turley et al., 2005

Past, Present and Future Aragonite Saturation Levels

Saturation Levels from Orr et al., 2005

Conclusions1. Detailed studies of the inorganic carbon system can help us to

better understand the physical and biological processes in the ocean.

2. Rising CO2 levels and global climate change will affect the processes controlling the distribution of carbon in the ocean, but what will be the net effect from the full range of forcing?

3. The unique circulation and biogeochemistry of the Indian Ocean may provide for an ocean response to climate change that is different from other oceans.

4. Additional carbon studies and sustained carbon measurements are needed to better understand the evolution of the carbon system in the Indian Ocean.

The R/V Thomas G. Thompson arriving in Papeete, Tahiti for the beginning of P16N February 2006

Stay Tuned for I8S/I9N in Feb./March 2007

Thank You!

CLIVAR/CO2 Repeat Hydrography

Calcium Carbonate Dissolution

CaCO3 + H20 + CO2 = Ca2+ + 2HCO3

- ∆CaCO3dis = 0.5 (NTAlk – NTAlko) + 0.63(0.0941 * AOU) NTAlk = (TALK * 35.0)/Salinity TAlko = 136.7 + (61.64 * Salinity) + (0.1004 * PO) – (0.579 * θ) PO = O2 + 170 * HPO4

2- (after Broecker, 1974) Respiration Coefficients from Anderson and Sarmiento (1994)

Preformed TAlk from Sabine et al. (1999)

Ocean Acidification in the 21st Century

Orr et al. 2005 (Nature)Orr et al. 2005 (Nature)

Δ[CO32-]Aragonite

http://www.ipsl.jussieu.fr/~jomce/acidification

H2O + CO2 + CO32- 2HCO3

-

acid antacid

Δ[CO32-] = [CO3

2-] — [CO32-]sat

Expect dissolution of pteropods, corals