EFFECTS OF THE FIEBERLING SEAMOUNT GROUP UPON FLOW AND THERMOHALINE STRUCTURE IN THE SPRING OF 1991

The circulation and thermohaline structure around Fieberling, Fieberli ng II and Hoke seamounts are examined on the basis of two high-resolut ion surveys in April and May 1991. The large-scale flow approached the seamounts from the southeast, impinging first on Hoke, then splitting , with one branch meandering westward in jetlike fashion over the Fieb erling II and Fieberling seamounts and the other turning to the northe ast. The jets were typically 10-20 km wide, with core speeds of 0.2-0. 5 m/s and were accompanied by pairs of cyclonic and anticyclonic eddie s, with diameters of 10-30 km, located near the seamounts. While the l arge-scale flow pattern persisted over a week, significant changes wer e observed in the shape of the meanders and the locations of the eddie s over this period. Transient, bottom intensified upwelling cones, 20 km in diameter and 150-220 m high, were encountered on all three seamo unts investigated, as were pronounced 60-m-deep mixed layers above the summits. Their persistence at a given location was less than a week. Geopotential height perturbations of the order of 0.8 J/kg (equivalent to 0.08 m in elevation) were observed in the vicinity of the seamount s. These perturbations are dominated by mesoscale ridges, troughs, pea ks, and depressions, the positions of which vary with depth as well as time. In general, the surface geopotential topographies differ in sha pe from those observed at depths where the seamount peaks occur, which is attributed to the vanishing influence of the California current be neath 200 m.