Observation-based Trends of the Southern Ocean Carbon Sink

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 pCO2 data underlying this trend reversal are sparse, requiring a substantial amount of extrapolation to map the data. Here, we use 9 different pCO2 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 8 of the 9 products agreeing on the sign of the decadal trends, i.e., a weakening CO2 sink trend in the 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 multi-product 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.