On the Reemergence of North Atlantic SST Anomalies

Abstract

The reemergence mechanism, whereby temperature anomalies extending over the deep winter mixed layer are stored beneath the surface in summer and are reentrained into the mixed layer when it deepens again in the following autumn and winter, is studied in the North Atlantic using approximately 40 years of surface and subsurface data. Reemergence is found to be robust in the Sargasso Sea and the northeast Atlantic, regions where (i) the mixed layer is much deeper in winter than in summer, (ii) currents are relatively weak, and (iii) temperature anomalies are coherent over broad areas. The two leading empirical orthogonal functions of North Atlantic SST anomalies also exhibit strong reemergence signatures. A novel application of empirical orthogonal function analysis to temperature anomalies in the time–depth plane, which also incorporates information from all grid points, is shown to be an efficient and useful approach for detecting reemergence without dependence on specific spatial patterns or prior selection of regions.