Hydrographic features of Magellan and Fuegian inland passages and adjacent Subantarctic waters

Hydrographic features and bottom profiles along the main passages from Paso Ancho in the Straits of Magellan to the Beagle Channel and those of adjacent oceanic waters are examined with regard to water origin and circulation. Sills and shallow entrances likely limited water exchange. Adjacent oceanic waters were warmest in the Atlantic and saltiest in the Pacific sectors. Waters within the inland passages were fresher and cooler than open shelf waters: showing a decreasing salinity gradient between the Beagle Channel and the Straits of Magellan and a subsurface wedge of warmest and saltiest oceanic water underneath a core of cold and brackish water in Brazo Noroeste. Subsurface water masses of the Straits of Magellan and Brazo Noroeste seem to be entrapped. Temperature and density distributions suggest that the inflow of salty and warm Pacific waters takes place through Bahia Cook. Westward and northward toward the Straits of Magellan, these waters may progressively mix with cooler and more brackish waters adjacent to Cordillera de Darwin. In this sector (Canal Brecknock-Canal Cockburn) stratification of the water column was weaker and became zero toward the Straits of Magellan (Seno Magdalena / Paso Ancho). Distribution of water properties was consistent with bathymetry profiles and suggests the following subdivision of microbasins along the Magellan-Beagle passage: 1.- Paso Ancho-Seno Magdalena, 2.- Canal Magdalena-Canal Brecknock, 3.- Canal Ballenero-Brazo Noroeste: 4.- Beagle Channel.