The oceanic sink for anthropogenic CO 2 : Combining observations with models

Transcription

1 The oceanic sink for anthropogenic CO 2 : Combining observations with models Nicolas Gruber 1,J,Orr 2 and OCMIP-members, C. Sabine 3 and GLODAP members, M. Gloor 4 and J. L. Sarmiento 5 (1) Institute of Geophysics and Planetary Physics & Department of Atmospheric Sciences, University of California, Los Angeles (2) Laboratoire des Sciences du Climat et de l Environnement CEA Saclay, Gif-sur-Yvette, France. (3) Joint Institute for the Study of Atmosphere and Ocean, University of Washington (4) Max Planck Institute for Biogeochemistry, Jena, Germany (5) Program in Oceanic and Atmospheric Sciences, Princeton University

2 Outline 1. The problem: From concentrations to fluxes 2. Forward Modeling: OCMIP-2 3. Inverse Modeling: First steps 4. Summary and Outlook

3 [m] [m] ANTHROPOGENIC CO 2 [µmol/kg] ATLANTIC SOUTHERN OC. PACIFIC 6 N 3 N Eq 3 S 6 S 6 S 3 S Eq 3 N 6 N Distance [km] Figure 4

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5 FORWARD AND INVERSE MODELING FORWARD MODELING e.g. surface fluxes MODEL Boundary conditions Initial conditions e.g. General Ocean Circulation Model Tracer distribution INVERSE MODELING Tracer distribution INVERSE MODEL e.g. Adjoint Model of OGCM e.g. surface fluxes Boundary conditions

6 ANTHROPOGENIC CO 2 FLUX (199) [molc/m2/yr] PRINCETON MODEL (L-L)

7 N N Pac Temp N Pac 6 7 N N Atl 1 Temp N Atl 2 12 Eq Indian Eq Pac 8&9 3 Eq Atl 13 Indian Pac 1 4 Atl 11&14 15 SubPol S Pac & SubPol S Ind Southern Ocean 11& SubPol S Atl

8 .2.1. OCMIP-2: ANTHROPOGENIC AIR-SEA CO 2 -FLUXES Southern Ocean AWI CSIRO IGCR IPSL.GM LLNL MIT MPIM NCAR NERSC SPol S PIUB Pac & PRINCE SOC SPol S Atl SPol S Ind & Pac Atl Pac Indian Eq Atl Eq Pac Eq Indian Temp N Atl Positive: Flux out of ocean Temp N Pac N N ATl N N Pac Flux [PgC/yr] Anthropogenic Fluxes -.6 <58 S 58 S - 36 S 36 S - 13 S 13 S - 13 N 13 N - 53 N 13 N - 36 N 53 N - 9 N 36 N - 62 N J. Orr and OCMIP-2

9 OCMIP-2: ANTHROPOGENIC CO 2 FLUXES, STORAGE, AND TRANSPORT J. Orr and OCMIP-2 (pers. comm)

10 OCMIP-2: Anthropogenic DIC along West Atlantic Track (North: TTO-1982; South: SAVE-1989) mmol kg -1 DATA (Gruber, 1998) [m] AWI CSIRO Longitude IGCR IPSL (GM) IPSL.DM1 (HOR) MIT NCAR SOC PIUB PRINCE PRINC

11 µmol kg DATA (Sabine et al., Unpublished) OCMIP-2: Anthropogenic DIC along WOCE P16 ( ) AWI CSIRO IGCR Longitude [m] IPSL IPSL.DM1 LLNL MIT MPIM NCAR NERSC PIUB PRINCE PRINC2 SOC UL

12 OCMIP-2: ANTHROPOGENIC CO 2 UPTAKE Uptake Rate (PgC/yr) Inventory (Pg) Model (S65) PRINCE IPSL.DM1(HOR) LLNL CSIRO MIT NCAR PRINC IPSL (GM) MPIM SOC IPSL.DM1(GM) IGCR PIUB AWI NERSC UL MEAN 1.99+/ / /- 12 RANGE "OBSERVATIONS*" 13 +/- 2 * Sabine et al. (pers. comm) J. Orr and OCMIP-2 (pers.comm.)

13 OCMIP-2: ANTHROPOGENIC CO 2 FLUX VERSUS CFC-11 INVENTORY AND VERSUS NATURAL C14 J. Orr and OCMIP-2 (pers.comm.)

14 Principle of Oceanic Inversion The ocean surface is partitioned into n regions. Basis functions Anthropogenic CO 2 Inversion In a OGCM, time-varying fluxes of dye tracers (Φ) are imposed in each of the n regions, and the model is run forward in time, i.e. for CO 2 (175-) Φ(t) = Φ(t =) (pco 2 (t) pco 2 (t = )) The model predictions of the dye concentrations are sampled at the observation stations and arranged as a vector χ OGCM. The model therefore provides us with a transport matrix A OGCM that relates the fluxes to the distribution, χ OGCM = A OGCMΦ. Modeled distributions at the observations stations are substituted with observed ones and the matrix A is inverted to get an estimate of the surface fluxes ( Φ est ): Φ est = A 1 OGCM χ obs.

15 INVERSE AIR-SEA CO 2 -FLUXES.8.6 Pre-industrial CO 2 flux Anthropogenic CO 2 Flux Positive: Flux out of ocean CO 2 Fluxes [Pg C/yr] Southern Ocean SPol S Atl Total CO 2 Flux SPol S Pac & SPol S Ind Atl Pac Indian Eq Atl Eq Pac Eq Indian Temp N Atl Temp N Pac N N ATl N N Pac <58 S 58 S - 36 S 36 S - 13 S 13 S - 13 N 13 N - 53 N 13 N - 36 N 53 N - 9 N 36 N - 62 N Anthropogenic CO 2 Flux: 1.8 PgC yr -1 Gloor et al. (submitted), Gruber et al. (in prep.)

16 .2.1. ANTHROPOGENIC AIR-SEA CO 2 -FLUXES Southern Ocean Inversion (KVLOW(h)) (199) Forward Model KVLOW (199) Forward Model KVHIGH (199) SPol S Forward Pac Model & OCMIP(199) mean SPol S SPol S Atl Ind & Pac Atl Pac Indian Eq Atl Eq Pac Eq Indian Temp N Atl Positive: Flux out of ocean Temp N Pac N N ATl N N Pac CO 2 -Fluxes [Pg/yr] Anthropogenic Fluxes -.6 <58 S 58 S - 36 S 36 S - 13 S 13 S - 13 N 13 N - 53 N 13 N - 36 N 53 N - 9 N 36 N - 62 N Gloor et al. (submitted), Gruber et al. (in prep.)

17 Summary and Outlook Despite fundamental differences between forward and inverse modeling of anthropogenic CO 2 fluxes, similar results emerge. Both methods indicate that the ocean south of 36 S takes up about 4% of the global anthropogenic CO 2. The second most important region for uptake are the tropics, followed by the North Atlantic. Substantial differences exist at more regional scales, with the Southern Ocean showing also the highest variations. Improvements need to made both on the modeling side as well as on the anthropogenic CO 2 reconstruction side. The challenge for the future consists in determining the anthropogenic CO 2 uptake in a changing ocean environment.