Short-term variations of deep water masses in Drake Passage revealed by a multiparametric analysis of the ANT-XXIII/3 bottle data

A multiparametric analysis is applied on the ANT-XXIII/3 bottle data to determine the spreading and mixing of water masses across Drake Passage during January-February 2006, focusing our interest on the flow of the deep water masses. Mixing proportions are quantified along both the southward and northward journeys between the tip of South America and the Antarctic Peninsula. The method is sensitive enough to detect a marked variability in the flow pathways of the Circumpolar Deep Water, the Southeast Pacific Deep Water (SPDW) and the Weddell Sea Deep Water at the intersection of the Shackleton Fracture Zone (SFZ) and the West Scotia Ridge (WSR) between the southward and northward journeys. Indeed the presence of a sharp meander of the southern branch of the Polar Front (PFS) together with the displacement of the northern branch of the Southern Antarctic Circumpolar Current Front (SACCFN) above the complex bathymetric structure of the WSR induced a strong perturbation in the deep flow field during the southward journey. The height of the SFZ crests clearly sets the lower limit of the SPDW in the Ona Basin. An enhanced δ3He signature is confined to the north of the Polar Front between 55.5°S and 56.5°S in the 1500-2200 m depth range. It clearly indicates the signature of the core of the Southeast Pacific Deep Slope Water. The entry pathway in the ACC of the SPDSW during ANT-XXIII/3 was farther to the south off the continental slope of South America than it was during the WOCE A21 expedition in 1990, probably due to the sharp changes in the slope orientation at the extreme tip of the South America.