Climate science: Ocean circulation drove increase in CO2 uptake

The ocean's uptake of carbon dioxide increased during the 2000s. Models reveal that this was driven primarily by weak circulation in the upper ocean, solving a mystery of ocean science. See Letter p.215 The ocean has absorbed about 40 per cent of anthropogenic CO2 emissions since the beginning of the industrial era, making it the largest CO2 sink. However, there is large decadal variability in the oceanic CO2 sink, and it has been difficult to attribute this variability to specific processes. This paper finds that variability in the ocean's overturning circulation has been the primary driver of changes in oceanic CO2 uptake over the past several decades. Weaker overturning since the year 2000, for example, has led to increases in oceanic carbon uptake.