DECADAL CHANGES IN OCEAN CARBON UPTAKE C.L. Sabine, R.A. Feely, G.C. Johnson, R. Wanninkhof, F.J. Millero, A.G. Dickson, N. Gruber, R. Key and P. Covert

DECADAL CHANGES IN OCEAN CARBON UPTAKE C.L. Sabine, R.A. Feely, G.C. Johnson, R. Wanninkhof, F.J. Millero, A.G. Dickson, N. Gruber, R. Key and P. Covert

Outline 1.Briefly review recent improvements in ocean carbon uptake estimates. 2.Discuss observational approaches for estimating changes in ocean uptake. 3.Illustrate a new potential approach for extrapolating ocean carbon measurements to basin and global scales. 4.Briefly touch on future needs.

Pre 1990s view of the global carbon cycle A missing carbon sink? Source: LDEO

WOCE/JGOFS/OACES Global CO 2 Survey ~72,000 sample locations collected in the 1990s DIC ± 2 µmol kg -1 TA ± 4 µmol kg -1 Mapped Inventory = 106±17 Pg C + marginal seas = 6± 6 Pg C + Arctic Ocean = 6± 6 Pg C Total Inventory = 118±19 Pg C Sabine et al., Anthropogenic CO 2 Column Inventory (mol/m 2 )

Recent assessments of 1990s ocean uptake Sabine and Feely, 2005

First 180 years the ocean absorbed 44% of emissions Last 20 years the ocean absorbed 36% of emissions 36% 43% 29% 13-23% 55-26% + to - Sabine and Feely, 2005

Is Ocean Carbon Uptake Changing with Time? If so, how do we monitor and understand these changes? OSP KNOT HOT BATS ESTOC One way is through long time-series measurements of carbon NZTS

U.S. JGOFS Time Series Measurements From: N. Gruber Gruber et al. (2002) Keeling et al. (2004) There are regional differences in the rate of ocean carbon increases

Another approach is CLIVAR/CO 2 Repeat Hydrography Goal: To quantify decadal changes in the inventory and transport of heat, fresh water, carbon dioxide (CO 2 ), chlorofluorocarbon tracers and related parameters in the oceans. Approach: Reoccupy a subset of the WOCE/JGOFS global survey cruises approximately every decade. The US has identified 19 cruises to be run over 10 years.

Achievements: The U.S. CLIVAR/CO 2 Repeat Hydrography Program has completed 6 of 19 cruises and is on schedule. For further details see: A16N June ‘03 A20 Sept. ‘03 A22 Oct. ‘03 P2 June. ‘04 P16S Jan. ‘05 A16S Jan. ‘05 U.S. CLIVAR/CO 2 Repeat Hydrography

Obtaining the decadal anthropogenic CO 2 signal in the ocean 1)Fit older cruise DIC as a function of non-carbon tracers 2)Use non-carbon tracers from new cruise to predict DIC 3)Examine difference between measured DIC and predicted DIC = a + bT + cS + dAOU + eNO 3 Multiple Linear Regression Approach Pressure (dbar) DIC (µmol/kg) ∆DIC (µmol/kg)

CO 2 Accumulation Rate on Isopycnal Surfaces along 30°N Based on P Comparison Vertically Integrated Accumulation: 1.1±0.1 mol m -2 yr -1

Preliminary results suggest that North Atlantic accumulation rate over the last decade may have been about half of the North Pacific accumulation rate. This appears to be a change from the historical operation of these basins. Water column Accumulation ~ 1.1 mol/m 2 /yr Water column Accumulation ~.6 mol/m 2 /yr SurfaceAccumulation 1.3 µmol/kg/yr SurfaceAccumulation 0.7 µmol/kg/yr

∆C T = DIC m - DIC MLR North Pacific Zonal section North Atlantic Meridional section For more information see Feely et al. and Wanninkhof et al. posters ∆DIC (µmol/kg)

How do we take observations from a few regions and evaluate basin-scale or global changes in uptake rate? Water column Accumulation ~ 1.1 mol/m 2 /yr Water column Accumulation ~.6 mol/m 2 /yr As we continue to expand our observational data base we need to focus on how to extrapolate results to basin and global scales SurfaceAccumulation 1.3 µmol/kg/yr SurfaceAccumulation 0.7 µmol/kg/yr

Is it possible to use ARGO to estimate carbon changes? Approach: Use MLR fits of shipboard data (A16N, A22, A20) to derive functions to estimate carbon from ARGO profiles. Measured Parameters: T, S, P, Lat., Lon N. A. ARGO Profiles

Physical Parameters used in MLR Fits: Potential Temperature (θ), Salinity (S), Potential Density (σ θ ), Spiciness (π), Brunt-Vaisala frequency (N 2 ) Examined Fits for a Variety of Carbon Parameters Rmse = 5.6 µmol/kg Rmse = 4.4 µmol/kg Rmse = 11.4 µmol/kg Dissolved Inorganic Carbon Total Alkalinity C* = DIC+0.688oxy- 0.5(Talk-0.094oxy) Measured Parameters: Temperature, Salinity, Pressure, Latitude, Longitude Rmse = 11.4 µmol/kg Rmse = 4.4 µmol/kg Rmse = 5.6 µmol/kg C* = DIC+0.688oxy- 0.5(Talk-0.094oxy)

Maps of North Atlantic C* Distributions ARGO based C* distributions agree well with data along sections and maps are consistent with expected patterns. WOCE C* maps appear to have significant mapping errors due to extrapolation between cruises. Approach: Use fits of modern hydrographic sections with ARGO profiles from same year to map C* values across basin. Map C* values from WOCE cruises Subtract WOCE maps from modern maps to determine anthropogenic accumulation.

Another complication with C* approach is the assumption of constant Redfield ratios. There appear to be large AOU changes on A16N that are of comparable magnitude to DIC changes. ∆AOU * (µmol/kg)

Rmse = 11.4 µmol/kg without oxygen Rmse =3.7 µmol/kg with oxygen Adding Oxygen Greatly Improves The Fit Adding oxygen to the global ARGO data base will make these data much more relevant for biogeochemical studies.

The technology is ready and being implemented by a handful of investigators, but needs large-scale implementation to be most effective Phase 2: Add pH to ARGO and use MLR fits of alk. to calculate full carbon system

Conclusions 1.Comparison of inventory changes over the first 180 years of the anthropocene with uptake rates for the last 20 years suggest that the ocean uptake is not able to keep up with atmospheric growth rate. 2.Time series and repeat hydrography data suggest that the North Atlantic uptake rate has been about half of the North Pacific rate for the last decade. 3.We are continuing to examine additional regions, but need to develop improved techniques for extrapolating results to basin and global scales. 4.Correlations between carbon and ARGO data are promising, but addition of oxygen sensors would greatly improve usefulness for biogeochemical studies.

On to our Next Cruise - P16N in 2006! On to our Next Cruise - P16N in 2006! Thank You!

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