OBSERVATIONS OF SEAMOUNT-ATTACHED EDDIES IN THE NORTH PACIFIC

Satellite-tracked drifters were used to examine eddy activity in the v icinity of the Emperor Seamount Chain (ESC) in the North Pacific durin g 1991-1993. The trajectories of two drifters drogued at a depth of 12 0 m revealed a pair of counterrotating mesoscale eddies attached to th e leeside of Ojin/Jingu Seamount in the summer of 1992. The eddies had diameters of 75-100 km and rotational speeds of 20-40 cm/s at 120 m. Sea surface height anomalies derived from blended TOPEX/ERS-1 satellit e altimetry revealed that the eddies had a surface manifestation as we ll. One of the drifters made five loops within the cyclonic eddy over a period of 62 days, during which time the eddy translated westward, t oward the seamount, at 2.9 cm/s. This is one of the first observations demonstrating an extended attachment of a topographically generated e ddy to a seamount. Drifters drogued at a depth of 15 m which crossed t he ESC in the summer of 1991 and winter of 1993 revealed no eddy activ ity, most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the Nintoku Seamount (summit depth at 1000 m). The implication is that eddy formation withi n the mixed layer near the ESC is confined to the region around the ta ller Ojin/Jingu and Kinmei Seamounts (summit depths at 800 m and 100 m , respectively). It is suggested that long-lived eddies attached to th e leeside of the ESC can profoundly influence local biological product ion and water exchange between the western and eastern basins of the N orth Pacific.