A subsurface warm‐eddy off northern Baja California in July 2004

Abstract

Upper‐ocean eddies are commonly observed from remote sensing, but submerged eddies are more difficult to detect. During July 2004, a 21‐day hydrographic survey in the southern region of the California Current was carried out to investigate the mesoscale variability. We observed for the first time a subsurface anticyclonic eddy off northern Baja California with the same water mass characteristics as the California Undercurrent. The core of the eddy was quasi‐circular with radii of 35 km and thickness of 250 m. The maximum swirl velocity was ∼3 cms −1 . The water mass of the core of the eddy was characterized by potential temperature of 11°C, salinity of 34.5, and dissolved oxygen of 1.4 mll −1 . The eddy propagated westward. The subsurface warm‐eddy could transport relatively saline water into the North Pacific subtropical gyre.