General Hydrography of the Beagle Channel, a Subantarctic Interoceanic Passage at the Southern Tip of South America

The Beagle Channel (BC) is a long and narrow interoceanic passage (?270 km 1–12 wide) with west-east orientation complex bathymetry connecting the Pacific Atlantic oceans at latitude 55°S. This study first integrated assessment of main oceanographic features BC, using recent observations from cruises, moored instruments historical observations. waters transported into BC are supplied mainly by Cape Horn Current, which carries Subantarctic Water (SAAW) depth (100 m below surface) along Patagonian continental shelf break. SAAW enters via submarine canyon western entrance BC. diluted fresh, nutrient depleted (nitrate, phosphate silicic acid) Estuarine (EW) Cordillera Darwin Ice Field (CDIF) forming modified (mSAAW). Freshwater inputs CDIF generate two-layer system sharp pycnocline delimits vertical distribution phytoplankton fluorescence (PF). Two shallow sills (<70 m) contribute to EW mSAAW mixing homogenization entire water column east sills, coherent Bernoulli aspiration. central section extending ?100 toward east, filled salty (31–32) variety EW. In winter, this nearly vertically homogeneous low concentrations (0.9–1.1 ?M PO4 7.5–10 NO3) PF. temporal variability seawater temperature 50 195 in was found be mostly dominated annual semiannual cycles influenced tidal forcing. middle less oceanic its basin-like structure most likely favors retention, observed weakly stratified mooring site. Toward disrupted Mackinlay Strait where another sill separates channel eastern that connects Ocean. section, formed when eastward surface outflow (salty-EW) flows over deeper, denser tongue mSAAW.