Changes in the ocean transport through Drake Passage during the 1980s and 1990s, forced by changes in the Southern Annular Mode

[ 1] We present the first direct evidence that interannual changes in ocean transport through Drake Passage are forced by variability in the Southern Annular Mode ( SAM). This evidence is derived from two decades ( 1980s and 1990s) of subsurface pressure measurements from the tide gauge at Faraday station ( western Antarctic Peninsula), combined with the output of an ocean general circulation model. In recent decades, the SAM has moved toward a higher-index state ( stronger circumpolar winds); this trend is not simply monotonic, but is the product of a long-term change in the seasonality of the SAM. Whilst we cannot address directly the effect of the long-term trend on circumpolar transport, bottom pressure data from Drake Passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the SAM. This offers a mechanism for atmospheric climate change to influence directly the large-scale ocean circulation.