Mesoscale flow and thermohaline structure around Fieberling seamount

Abstract

The circulation and thermohaline structure around Fieberling and the three neighboring seamounts to the ESE are examined on the basis of high‐resolution observations in August 1989. In the upper layers, the primary interaction is with well‐defined intrusions of water of subtropical and subarctic origin, linked to the outer boundary of a southward meandering California current. The effects of flow‐topography interaction are complex and vary with depth. At the level of Fieberling's top, about 450 m, the impinging subtropical flow is deflected anticyclonically, and several eddies are generated. Uplift of isopycnals suggestive of upwelling is observed above the tops of all four seamounts. The height of the upwelling cones varies between 120 and 240 m, depending upon background stratification, and their axes are sometimes tilted, apparently by shear of the large‐scale flow. Strong subsurface jets, 10–20 km wide and 500–1000 m thick, with speeds up to 30 cm/s, have been found in the vicinity of the seamounts. In the lower layers the primary interaction is with large‐scale flow from the southeast. The flow is deflected anticyclonically around the seamount group as a whole, with individual branches of this flow passing through the larger gaps between seamounts. The observations are compared with simple models of subinertial flow past individual and multiple seamounts. Though suggestive in predicting some of the observed features, the models need further development based on less restrictive assumptions on the impinging mean flow and the ambient density stratification.