Carboocean Second Annual Meeting Session on Seasonal and Interannual Variations of Air-Sea CO2 Flux.... in the Southern Ocean N.Metzl, LOCEAN-IPSL thanks to A.Lenton, O. Aumont, K. Rodgers, T.Takahashi Message 1: Seasonality and annual CO2 flux Southern Ocean CO2 sink is low : to -0.2 PgC/yr (since 4 years, progress in observations and modelling) Message 2: Interannual variability when observed, controlled by biological activity not well simulated (limitations on co-limations ?)

Air-Sea CO2 flux climatogy Takahashi et al., (2002)

S.O. > 50°S: PgC/yr (against PgC/yr in T02) New climatology, Takahashi et al. (2006, OCCC, in prep)

Annual air-sea CO2 flux in the Southern Hemisphere Total > 50°S: PgC/yr New climatology (Takahashi et al., 2006, in prep; Gruber et al; 2006) Total > 50°S: PgC/yr Coherent view for annual CO2 flux Ocean Model (Aumont et al., 2004, see poster Lenton et al)

Back four years ago: Annual Flux in the Southern Ocean: OCMIP II models Pg/yr, Climatology, –0.35 Pg/yr !!!! Same annual flux, but opposed seasonality biological and mixing processes not correct in ocean models summer winter summer

Before discovering that rats love frogs, before ice melts in the future…. before concluding on annual fluxes, simulations need first to be seriously validated at seasonal scale - Validate oceanic processes and forcings - It is expected that pCO2 seasonality would change in the futur (positive, negative feedbacks ?)

pCO2 tracks, all seasons (CARBOOCEAN database, B.Pfeil with help from A.Kozyr, CDIAC and.... all contributors) Looking for seasonal observations

Seasonality in South Indian Ocean: Large Variations in all Regions Ice Summer Sink Summer Source Winter Source Winter Sink Metzl et al., 2001, DSR 2006

Seasonal cycle in the Sub-Antarctic Zones (well observed) Western and Eastern Indian Ocean, Monthly Mean (Sink: -0.4 PgC/yr in the Indian SAZ) Metzl et al. 1999, Tellus Summer sink Winter equil Seasonal Range 60 µatm

Southern Ocean > 50°S, in the POOZ Observations in January and August: what is the annual cycle ??? ????

Seasonality in the POOZ (western Indian sector) Observations and 1D box-model summer sink, bio >> warming winter source, MIX >> cooling Metzl et al., 2001, DSR, 2006 Extrapolation S.O. >50°S: = PgC/yr, POOZ: PgC/yr + SIZ: PgC/yr Seasonal Range 40 µatm

Monthly Air-sea CO2 fluxes (Ocean model, PISCES-NOCES) 20 years of seasonality at latitude >50°S summer sink winter source

Seasonal Cycle: Regional observations and ocean models good phasing, encouraging

Seasonal cycle: observations, ocean models, climatology, atm. inversions not bad: summer sink/ winter source or equilibrium

Average: PgC/yr Interannual CO2 flux in the Southern Ocean >50°S: A view from an ocean model (between -0.1 and 0.1 PgC/yr)

OISO Kerguelen Amsterdam Crozet La Réunion OISO cruises onboard R.V. Marion-Dufresne Western Indian - Antarctic Sector

Interannual Variability Observed in the Southern Indian Ocean (6 OISO cruises conducted in the same region during January) Air 2004 Air 1998 SIZPOOZ Metzl, IGBPnews 2005, and unp. res. Interannual Range 50 µatm

Interannual variability of air-sea CO2 fluxes in the S.O. (sector POOZ Indian Ocean) (observed pCO2 water and air, Wind Quickscat + Wanninkhof 92)

These variations are not captured in physical-biological models (e.g. see poster Lenton et al.) High Chl-a event, low fCO2 axis reversed Interannual variability of Chla in the POOZ, Indian sector good candidate to explain the decrease of the CO2 sink since 1998

Carboocean Second Annual Meeting Session on Seasonal and Interannual Variations of Air-Sea CO2 Flux.... in the Southern Ocean Message 1: Seasonality and annual CO2 flux Southern Ocean CO2 sink is low : to -0.2 PgC/yr (since 4 years, progress in observations and modelling) Message 2: Interannual variability when observed, controlled by biological activity not well simulated (limitations on co-limations ?) Message 3: If seasonality is well reproduced (happy), but not interannual variability (maybe not dramatic ?) what analysis need to be performed in priority (1-3 years) to better understand future scenarios and feedbacks.