VARIABILITY OF OCEAN CO 2 PARTIAL PRESSURE AND AIR-SEA CO 2 FLUXES IN THE SUBANTARCTIC ZONE OF THE SOUTHERN OCEAN J. Boutin (1), L. Merlivat (1) and K. Currie (2) (1) LOCEAN, Paris, France (2) NIWA, New Zealand

Year Nb CARIOCA buoys Duration of pCO 2 meas. (Months) Ship tracks used for building Takahashi climatology (from Li et al, 2005) + Trajectories of 8 CARIOCA buoys deployed in the Southern Ocean,

CARIOCA drifters Hourly measurements (real time ARGOS transmission) Ocean measurements at 2m depth: –pCO 2 (accuracy <3  atm) –SST –SSS –Fluorescence Atm. measurements of: –Wind speed –Atm. Pressure Trajectory influenced by : –15m depth currents Lifetime: up to 17 months DIC deduced from pCO2, SST and SSS assuming Alk/SSS relationship (Jabaud et al., 2004)

Air-sea CO 2 flux computation F Air-sea CO 2 flux =K(U,sst) CO 2 exchange coefficient.(pCO 2 – pCO 2 atm ) CO 2 partial pressure difference (pCO 2 atm very homogeneous) K derived from satellite or CARIOCA wind speed (U) via Wanninkhof (1992) K-U relationship pCO 2 atm deduced from xCO 2 and CARIOCA Patm Sonic Anemometer on CARIOCA in => 17 months of wind measurements on each buoy; precision CARIOCA / QSCAT satellite wind speeds: 1.3m/s 20 QSCAT wind speed (m/s) CARIOCA wind speed (m/s)

Large flux variability dominated by  P variability (no clear seasonal cycle)

Large differences in flux and  P after July 2004: Mean fluxes: Northern buoy: -9.6 mmol m -2 day -1 ; Southern buoy: -5.0 mmol m -2 day -1 March/April 04 –June/Sept. 05 Southern buoy Northern buoy

Comparison with Takahashi(2002) climatology North-South/East-West gradient structure seen by the buoys qualitatively coherent with yearly  p Takahashi mean in the western Pacific ( )

 p time and space colocation with Takahashi climatology Mean  p along CARIOCA trajectory: North Carioca : -35  atm South Carioca : -16  atm North Taka : -17  atm South Taka : -13  atm Large scale spatial/temporal structures coherent but : -West and North  p measured by CARIOCA lower than Takahashi : interannual variability? Oceanic trend different from atmospheric trend between 1995 and 2005? -small scale structures on CARIOCA data

pCO 2 In Winter : -Southern buoy close to the SAF as defined by Belkin and Gordon (1996) -Southern buoy travels much faster than Northern buoy => Southern buoy probably in a jet on SAF High pCO2 recorded by the Southern buoy close to the SAF front Interpretation of North-South gradient

pCO 2 DIC SAF signature even clearer on DIC

pCO 2 - SST relationship derived from CARIOCA in Winter and from ship data south of Tasmania and New Zealand Atm. trend Close to NZ coastal province Close to SAF pCO 2 anticorrelated with SST close to SAF => evidence of mixing Similar slope as the ones detected from ship data south of Tasmania and New Zealand (Rangama et al., JGR, 2005)

Interpretation of CARIOCA data using ocean color SAF Satellite Chl images, a tracer of ocean circulation Mixing also responsible for high Chl in Spring as seen on satellite MODIS ocean color image (November month) ? Chl (mg/m 3 )

One month later (December 2004) a bloom developed north of SAF => strong mesoscale variability on northern buoy Interpretation of CARIOCA data using ocean color

December 2004, northern buoy, pCO 2 and DIC decrease associated with the development of a Chl bloom fCO Chloro-a DIC  mol/kg)  atm) 21/12 29/12

SUMMARY -No clear seasonal cycle in the Subantarctic Zone (SAZ); variability dominated by spatial and small scale variability -Close to Subantarctic front: mixing is the dominant mechanism controlling pCO2 variability; agreement with Takahashi climatology -North/South-East/West structures similar to Takahashi climatology But lower pCO 2 in the north and west part of the SAZ in the Pacific Ocean

SUMMARY -No clear seasonal cycle in the Subantarctic Zone (SAZ); variability dominated by spatial and small scale variability -Close to Subantarctic front: mixing is the dominant mechanism controlling pCO2 variability; agreement with Takahashi climatology -North/South-East/West structures similar to Takahashi climatology But lower pCO 2 in the north and west part of the SAZ in the Pacific Ocean NEXT STEP How to reconcile air-sea fluxes estimated at regional scale by indirect methods (model inversions) and from surface ocean observations in the Southern Ocean? pCO 2 space/time extrapolation? -Need to refine biogeochemical provinces first defined by Longhurst (1998) (northern and southern buoys under the influence of different processes although in the same Subantarctic water ring province)

SUMMARY -No clear seasonal cycle in the Subantarctic Zone (SAZ); variability dominated by spatial and small scale variability -Close to Subantarctic front: mixing is the dominant mechanism controlling pCO2 variability; agreement with Takahashi climatology -North/South-East/West structures similar to Takahashi climatology But lower pCO 2 in the north and west part of the SAZ in the Pacific Ocean NEXT STEP How to reconcile air-sea fluxes estimated at regional scale by indirect methods (model inversions) and from surface ocean observations in the Southern Ocean? pCO 2 space/time extrapolation? -Need to refine biogeochemical provinces first defined by Longhurst (1998) (northern and southern buoys under the influence of different processes although in the same Subantarctic water ring province) Climatological Longhurst biogeochemical provinces Subantarctic water ring subtropical NZ

SUMMARY -No clear seasonal cycle in the Subantarctic Zone (SAZ); variability dominated by spatial and small scale variability -Close to Subantarctic front: mixing is the dominant mechanism controlling pCO2 variability; agreement with Takahashi climatology -North/South-East/West structures similar to Takahashi climatology But lower pCO 2 in the north and west part of the SAZ in the Pacific Ocean NEXT STEP How to reconcile air-sea fluxes estimated at regional scale by indirect methods (model inversions) and from surface ocean observations in the Southern Ocean? pCO 2 space/time extrapolation? -Need to refine biogeochemical provinces first defined by Longhurst (1998) (northern and southern buoys under the influence of different processes although in the same Subantarctic water ring province) -Acquire new data sets in the Southern Atlantic Ocean: deployment of 6 CARIOCA buoys in the frame of CARBOOCEAN (EU integrated FP6 project ).