Estimation Of Air-Sea CO₂ Flux In The Southern Ocean Via In-situ And Remote Sensing Data

The southern ocean plays a key role in the exchange process with atmosphere of natural and anthropogenic CO₂.In this study,we applied remote sensing data in comparison with the in situ investigation data to quantitatively express air-sea fluxes of pCO₂ in the region,from 50°S to 75°S and from 60°W to 80°E in the Southern Ocean.The empirical relationships between underway measured pCO₂ and shipboard Chl-a,sea surface temperature(SST) on board RV Xuelong were used to calibrate Chl-a and SST to create pCO₂ field in the remotely sensing datasets.Weekly and monthly maps of the air-sea CO₂ flux in the interested regions were further developed using the remotely sensed wind speed data from QuikSCAT dependence of the CO₂ gas transfer velocity of Wanninkhof,remotely sensed SST data from AVHRR and observed marine salinity data,atmospheric CO₂ data offered by the World Ocean Atlas by NOAA during the period CHINARE(Chinese Antarctic Research Expeditions)-â…©â…¥(1999.12～2000.1) and CHINARE-â…©â…ª(2004.12～2005.1) respectively.The results show regional spatial and temporal variabilities of air-sea flux of pCO2 in the Southern Ocean(south of 50°S) in the austral summer,and improve the accuracy of estimating the uptake of atmospheric CO₂ in the Southern OceanResults can be mainly summarized as the followings:1.The result reveals the pattern of chlorophyll accumulation gradiently alongshore over the summer,with lower concentrations offshore.Large phytoplankton blooms occur particularly in waters around ice edges and islands as well as in polynyas and continental shelves.Sea surface temperature increases gradiently from south to north associated with time when summer coming.The strongest upwelling of the Circumpolar Deep Water is expected to occur at the Antarctic Divergence(73°E,64°S) and in the region center with(0°E,65.5°S).The sea surface salinity shows an irregular spatial patch distribution with higher or lower value.In January,the sea surface salinity decreases for the melted fresh water.In the austral summer,wind speed 10 meters above the sea surface turn to the lowest in the whole year.West wind is dominant in the austral summer south of 40°S in the southem ocean.2.The waters from 60°W to 80°E in the Southern Ocean is a sink of CO₂ from atmosphere during austral summer,pCO₂ distribution shows spatial and temperal variability.The sink magnitude can be sequenced as:the south Atlantic sector＞south Georgia and the Falkland island＞the Antarctic peninsula＞inner part of the Prydz bay＞south Indian sector＞Weddell sea＞outer part of the Prydz Bay.3.Using a model of CO₂ flux,the net uptake of atmospheric CO₂ in the Antarctic Ocean is 0.068GtC,0.072 GtC,0.071 GtC,0.074 GtC in Dec,1999, Jan,2000,Dec,2004 and Jan,2005 respectively.The annual net uptake in the Antarctic Ocean is 0.476 GtC,0.489 GtC,0.511 GtC,0.518 GtC in 1999, 2000,2004 and 2005 respectively,which contributes 25%to the total uptake in the global ocean.The net uptake of CO₂ in the Antarctic Ocean increases annually especially in the region as a strong sink,the Weddell sea,south Georgia,Falkland islands,the Antarctic Peninsula and the south Atlantic sector,while in the south Indian sector,the net uptake of CO₂ decreases.