Long-term changes in the North Atlantic current system and their biological implications

Synopsis Evidence is presented to show that the dominant mode of temperature change of the last 25 years, in the North Atlantic, has recurred throughout the last 100 years. Temperatures in the NE Atlantic, where this mode is especially prominent, tend to be inversely related to the strength of the Trade and Westerly Winds. The mode of temperature change, which extends through the top 250 m and involves corresponding salinity changes in the NE Atlantic, is interpreted as resulting from a shift in the North Atlantic Current system, wind-induced increases in the transport of the North Atlantic Gyre being accompanied by a radial shrinkage of the current system and a reduction of the warm water discharge to the north. A theoretical analysis, relating this current change to a shift in the separation of the Gulf Stream from the North American coast, is attempted to examine the consequences of this interpretation