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An up‐to‐date map of the Antarctic Circumpolar Current (ACC) fronts is constructed from the latest version of mean dynamic topography (MDT) from satellite altimetry and reveals the narrowest ACC width in the Udintsev Fracture Zone (UFZ), with the strongest concentration of the three major ACC fronts within a limited distance as short as 170 km, about 40% narrower than that at Drake Passage. At 144°W, at the entrance of the UFZ, which lies between the Pacific‐Antarctic Ridge (PAR) and its eastwardly offset segment (offset PAR segment), there is a triple confluence of the Subantarctic Front, Polar Front, and Southern ACC Front. Downstream of this longitude, the Subantarctic Front progressively meanders northward over the relatively shallow offset PAR segment before channeling through the Eltanin Fracture Zone, thus diverging from the Polar Front which proceeds through the UFZ. In situ observations from two recent cruises at 144°W confirm the satellite altimetry‐derived frontal circulation in the UFZ region and yield a baroclinic transport relative to the bottom of 113 × 106 m3/s, comparable to that through Drake Passage. The hydrographic sections show no Antarctic bottom water colder than 0.2 °C. Characteristics of major water masses are described, and the implications for their potential downstream modifications at Drake Passage are discussed in terms of the meridional overturning circulation across the ACC. Mesoscale eddy activity with periods shorter than 90 days is predominantly concentrated in the immediate downstream area of the offset PAR segment, suggesting a substantial poleward eddy heat flux there. Key Points: The Antarctic Circumpolar Current is only 170 km wide in the Udintsev Fracture Zone, forming the narrowest circumpolar choke pointFirst observations of high‐quality hydrography in the Udintsev Fracture Zone show no Antarctic bottom water colder than 0.2 °CThe Udintsev Fracture Zone is a suitable site for a long‐term monitoring of the Antarctic Circumpolar Current [ABSTRACT FROM AUTHOR]

Abstract: 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 1500–2200m 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. [Copyright &y& Elsevier]