An XBT section with station intervals of 11 km, from 45¿ to 35¿S along 92¿W, taken February 1979, provides the first clear picture of the meridional thermal structure across the west wind drift in this sparsely sampled transition zone. At least two mesoscale isotherm structures are found which show vertical excursions of up to 250 m over horizontal distances of about 70 km and vertical coherence to depths of sampling limit at 1600 m; locations appear coincident with major ridge features in the Chile Rise. The inferred westward flow patterns are evaluated as possible source mechanisms for the tongue of low-salinity surface water known to extend westward from the Chile coast.