Observation‐Based Trends of the Southern Ocean Carbon Sink

Abstract

Abstract The Southern Ocean (SO) carbon sink has strengthened substantially since the year 2000, following a decade of a weakening trend. However, the surface ocean p CO 2 data underlying this trend reversal are sparse, requiring a substantial amount of extrapolation to map the data. Here we use nine different p CO 2 mapping products to investigate the SO trends and their sensitivity to the mapping procedure. We find a robust temporal coherence for the entire SO, with eight of the nine products agreeing on the sign of the decadal trends, that is, a weakening CO 2 sink trend in the 1990s (on average 0.22 ± 0.24 Pg C yr −1 decade −1 ), and a strengthening sink trend during the 2000s (−0.35 ± 0.23 Pg C yr −1 decade −1 ). Spatially, the multiproduct mean reveals rather uniform trends, but the confidence is limited, given the small number of statistically significant trends from the individual products, particularly during the data‐sparse 1990–1999 period.