Anatomy of the Antarctic Circumpolar Current Volume Transports through Drake Passage.

A 20 year long volume transport time series of the Antarctic Circumpolar Current across the Drake Passage was estimated from the combination of information from in situ current meter data (2006–2009) and satellite altimetry data (1992–2012).

 The time series of three transport components (total (TT), barotropic (BT), and baroclinic (BC)) present energetic intraseasonal fluctuations, with a salient spectral peak at 50 and 36 days, with the largest (least) variance being associated with the BT (BC) component. Low-frequency variations are much less energetic with a significant variance limited to the annual and biannual timescales and show a non-stationary intermittent link with the Southern Annular Mode and the Nino 3.4 index for interannual timescales.

The intraseasonal transport variations are mostly associated with intrinsic local modes in the Yaghan Basin (northern Drake Passage). The region around 57°S in the Yaghan Basin appears to be a strategic point for a practical monitoring of the ACC transport. These local BT (and TT) variations are associated with a well-defined tripole pattern in altimetric sea level anomaly (SLA). There is evidence that the tripole pattern associated with BT is locally generated when the BC-associated meso-scale SLAs, which have propagated eastward from an upstream area of DP, cross the Shackleton Fracture Zone to penetrate into the Yaghan Basin. Barotropic basin modes excited within the Yaghan Basin are discussed as a plausible mechanism for the observed energy-containing spectral peaks found in the transport variability.