Recent increase in oceanic carbon uptake driven by weaker upper-ocean overturning.
The ocean is the largest sink for anthropogenic carbon dioxide (CO2), having absorbed roughly 40 per cent of CO2emissions since the beginning of the industrial era. Recent data show that oceanic CO2uptake rates have been growing over the past decade, reversing a trend of stagnant or declining carbon uptake during the 1990s. Here we show that ocean circulation variability is the primary driver of these changes in oceanic CO2uptake over the past several decades. We use a global inverse model to quantify the mean ocean circulation during the 1980s, 1990s and 2000s, and then estimate the impact of decadal circulation changes on the oceanic CO2sink using a carbon cycling model. We find that during the 1990s an enhanced upper-ocean overturning circulation drove increased outgassing of natural CO2, thus weakening the global CO2sink. This trend reversed during the 2000s as the overturning circulation weakened. Continued weakening of the upper-ocean overturning is likely to strengthen the CO2sink in the near future by trapping natural CO2in the deep ocean, but ultimately may limit oceanic uptake of anthropogenic CO2.
Department of Geography, University of California, Santa Barbara, California 93106, USA.|Earth Research Institute, University of California, Santa Barbara, California 93106, USA.
Tim
T
DeVries
School of Mathematics and Statistics, University of New South Wales, Sydney, New South Wales 2052, Australia.|Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
Mark
M
Holzer
Department of Earth System Science, University of California, Irvine, California 92697, USA.
Francois
F
Primeau
D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism; D057965:Carbon Sequestration; D006802:Human Activities; D009792:Oceans and Seas; D012623:Seawater / Q000032:analysis / Q000737:chemistry*
D002245:Carbon Dioxide