Circulation in the Ona Basin, southern Drake Passage

Abstract

Five Argo floats trapped in the Ona Basin, in the southern Drake Passage, provided unprecedented information on the water masses and the circulation present in all the seasons from March 2002 to April 2006. Their profiles recorded evidence of deep-penetrating eddies, interleaving of water masses, and branching of the Southern Front of the Antarctic Circumpolar Current as it meets the Shackleton Fracture Zone. Ten-day mean-velocity estimates at the float parking depth ( 2000 db) often exceeded 15 cm s(-1), revealing the intensity of the mesoscale field. Satellite data showed that the trapping period of the floats corresponded to the presence of an anticyclonic meander of the polar front over a depression in the topography to the northwest of the Ona Basin. The presence of this meander seems to be linked to low-frequency modes of variability in sea surface height in the Yaghan Basin.