The large-scale context for oceanic subduction in the Northeast Atlantic

The large-scale context for oceanic subduction is examined in the region bounded by 10°N and 40°N and 10°W and 40°W using data collected from June 1991 to June 1993. In contrast to climatology, it was found that over the entire region the ocean gained heat, ranging from 10–30 W m–2 to the north to 40–50 W m–2 to the south. Steady tradewinds dominated the southeastern half of the region. To the northwest of the axis of these tradewinds was a broad region of downward Ekman pumping with a 2-yr mean of about 50 m yr–1. Wind-driven surface currents and a seasonal cycle in mixed layer temperature and depth were found that reflected the influence of local forcing. The interior circulation was consistent with the clockwise circulation of the eastern end of the subtropical gyre, though eddy variability dominated the northern part of the region. Due to Ekman convergence the winter mixed layer in the central and southwestern parts of the region was as deep as to the north; however, it was also warm. This deep, warm mixed layer in the center of the region aided the subduction of water from the northeast by providing a protective cap; isopycnals that outcropped to the north passed well below the base of this mixed layer.