Upper ocean thermohaline, oxygen, nutrient, and flow structure near the date line in the summer of 1993

Abstract

An overview is given of the upper ocean geopotential height, zonal flow, thermohaline, oxygen, and nutrient structures between the Bering Sea and Fiji islands, based on high‐resolution field measurements along 179°E. The geopotential topography is dominated by large‐amplitude (2–4 J kg−1) mesoscale perturbations in the subarctic and subtropical gyres and a smoother equatorial ridge‐trough system. The fastest midlatitude zonal flows (40 cm s−1) are associated with the Alaska Stream, the Subarctic Current, the Kuroshio Extension, and the North Equatorial Current. Prominent physical and chemical frontal zones are observed between 42°–45°N and 12°–15°N. A pronounced upwelling dome is found south of the Aleutians, which brings dense, nutrient rich waters within 125 m of the sea surface. Well‐defined upwelling domes also occur in the northern (5°10°N) and southern (3°–8°S) doldrums. El Niño conditions prevailed near the equator in August 1993, marked by surface temperatures of 30°C, low salinities, low nutrient concentrations, eastward surface flow (30 cm s−1), merging of the North Equatorial Countercurrent and Equatorial Undercurrent (50 cm s−1), absence of trade winds and abundant rainfall, and southward displacement of the South Equatorial Countercurrent (20 cm s−1). The South Equatorial Current (20 cm s−1) has a complex multicore structure and is accompanied by a major physical and chemical frontal zone between 13°–16°S. A fast coastal eastward jet is observed on the north slope of Vanua Levu island, Fiji.