Inorganic Carbon Distributions and Air-Sea CO 2 Exchange in the Indian Ocean

Transcription

1 Inorganic Carbon Distributions and Air-Sea CO 2 Exchange 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

2 Take home message: Each of the 4 measurable carbon parameters can tell us something different about the basic processes operating in the Indian Ocean Gas Exchange pco 2 ph TCO 2 Ocean Physics TAlk Biology

3 The Most Comprehensive Look at Carbon Distributions Occurred in the 1990s as part of the WOCE/JGOFS/OACES Global Survey. More than 60 cruises with approximately 72,000 pairs of carbon measurements GLODAP synthesis is publicly available from CDIAC (NDP 083) Global Inventory of Anthropogenic CO 2 : 118±19 PgC North Atlantic has the largest column inventories of anthropogenic CO 2 (mol m -2 ).

4 Question for SIBER: How will ocean carbon system respond to changes in ocean processes? Gas Exchange Rising CO 2 Levels Changing Climate pco 2 ph Changing Biology? TCO 2 Ocean Physics TAlk Biology

5 Total Alkalinity: Surface Talk Distribution is Very Similar to Salinity

6 Shallow Indian Ocean Data (depth < 100 m)

7 Potential Alkalinity in Bottom Waters Follows Water Mass Age Potential Alkalinity = (Alkalinity + Nitrate) / Salinity * 35 ala Brewer et al., 1972

8 Global Carbonate Budget Flux term mmol CaCO 3 m -2 d -1 Gt PIC yr -1 Production or calcification in the euphotic zone Export from surface (models) Export from surface (traps, Pacific) Dissolution in upper 1500 m Atlantic Pacific Indian Total 1.0 Export to traps below 2000 m 0.38 ± ± 0.3 Dissolution on sea floor below 0.24 ± ± m (Atlantic and Pacific) Burial in Holocene sediments Berelson et al., 2006

9 Indian Ocean TA*: A Measure of CaCO 3 Dissolution

10 Anthropogenic CO 2 is causing carbonate saturation horizons to shoal in all oceans

11 TCO 2 : Surface Distribution is Similar to Nutrient Distributions

12 Shallow Indian Ocean Data (depth < 100 m)

13 Annual C mass balance Net Community Production Based on TCO 2 Distributions From Bates et al. GBC, GB3021, 2006 Annual C mass balance Monthly C variations suggest Northern IO is net autotrophic during NEM and SI and net heterotrophic during SWM and FI 787

14 ΔDIC for a 10 ppm change in pco 2 as a function of Revelle Factor Low Latitudes (ΔpCO 2 /ΔTCO 2 )/(pco 2 / TCO 2 ) Revelle Factor High Latitudes Lower latitudes are more efficient at taking up atmospheric CO 2

15 Zonal inventories of Anthropogenic CO 2 The uptake and storage of anthropogenic CO 2 in the Indian Ocean appears to be consistent with its size, but how might this change over time?

16 Preliminary results suggest that North Atlantic accumulation rate over the last decade may have been about half of the North Pacific accumulation rate. Surface DIC (µmol/kg) Water column Surface Cant (µmol/kg) Water column Accumulation Accumulation Accumulation Accumulation 1.3 µmol/kg/yr ~ 1.1 mol/m 2 26,70 /yr 0.7 µmol/kg/yr ~.6 mol/m2/yr +14 µmol 40 S 26,75 kg-1 +7 µmol kg -1 26,70 26,75 26,80 26,80 density 26,85 26,90 26, density 26,85 26,90 26, ,00 27,00 27,05 indigo oiso 27,05 indigo oiso 27,10 (Lo Monaco and Metzl, 2005) As the US repeat hydrography program moves into the Indian Ocean in we must ask how ocean carbon uptake is evolving in this region 27,10

17 pco 2 and sea-air CO 2 flux Global Net CO 2 Flux from Takahashi et al., 2002

18 CO 2 Seasonality: large variations in all regions Winter Source Summer Source fco2 (µatm) Ice Summer Sink Winter Sink Wat Jan 2000 Wat Aug 2000 Air Jan 2000 Air Aug Latitude Metzl et al., 2001, 2006

19 Surface pco 2 Patterns based on WOCE/JGOFS Cruises Surface waters can be fit with empirical functions to +/- 9 ppm (μatm) North of 15S is source of ~0.15 PgC/yr while 15S-50S is net sink of ~0.7PgC/yr

20 Surface water pco 2 variability controlled by interplay of thermal and biological effects, but wind speed variability also influences CO 2 fluxes. We know that seasonal variability is quite large, but what is the inter-annual variability?

21 Interannual variability : large in austral summer, including in warm waters of the subtropical Indian Ocean (based on 10 OISO cruises conducted in both summer and winter) 420 austral summer fco2 (µatm) SST ( C) austral winter oiso1 oiso2 oiso3 oiso4 oiso5 oiso6 oiso8 oiso9 oiso11 oiso12 Metzl, unpub.

22 Concept: Use Multiple Platforms to Produce Seasonal CO 2 Flux Maps Algorithm development pco 2 = f(sst, color) pco 2 maps In situ sampling pco 2, SST, SSS Co-located satellite data Apply algorithm to regional SST& color fields to obtain seasonal pco 2 maps Flux = k s pco 2 Regional satellite SST & color data Flux maps Remote sensing SST, color & wind Soon SSS Wind data Algorithm development Gas transfer, k = f (U 10,SST)

23 Generating a Global Seasonal Flux Map Based on NCEP II winds and SST Goal: Reduce average regional uncertainty in CO 2 flux to <0.2 PgC yr -1 Approach: 1. Improving regional relationships by incorporating additional parameters (e.g. mixed layer depth, chlorophyll) 2. Improving regional relationships using ship-based and moored pco 2sw observations

24 Surface ph distribution reflects combined patterns of alkalinity and TCO 2

25 ph Minimum Associated With O 2 Minimum shallow in Northern Indian Ocean

26 As long as CO2 continues to enter the ocean, ph will continue to drop After Turley et al., 2005 Caldeira and Wickett, Nature, 2003 The changing ph is important because it highlights a changing chemical speciation in the ocean

27 Past, Present and Future Aragonite Saturation Levels Saturation Levels from Orr et al., 2005

28 Conclusions 1. Detailed studies of the inorganic carbon system can help us to better understand the physical and biological processes in the ocean. 2. Rising CO 2 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.

29 Thank You! Stay Tuned for I8S/I9N in Feb./March 2007 The R/V Thomas G. Thompson arriving in Papeete, Tahiti for the beginning of P16N February 2006

30 CLIVAR/CO 2 Repeat Hydrography

31 Calcium Carbonate Dissolution CaCO 3 + H CO 2 = Ca HCO 3 CaCO 3dis = 0.5 (NTAlk NTAlk o ) ( * AOU) NTAlk = (TALK * 35.0)/Salinity TAlk o = (61.64 * Salinity) + ( * PO) (0.579 * θ) PO = O * HPO 2-4 (after Broecker, 1974) Respiration Coefficients from Anderson and Sarmiento (1994) Preformed TAlk from Sabine et al. (1999)

32 Ocean Acidification in the 21 st Century H 2 O + CO 2 + CO 3 2-2HCO 3 - Δ[CO 3 2- ] = [CO 3 2- ] [CO 3 2- ]sat acid antacid Δ[CO 3 2- ] Aragonite Orr et al (Nature) Expect dissolution of pteropods, corals