An Isopycnic Model Study of the North Atlantic. Part II: Interdecadal Variability of the Subtropical Gyre

Abstract In a companion paper, a spinup integration of the North Atlantic Ocean with the Miami isopycnic-coordinate model was presented. The wintertime mixed layer in the central North Atlantic was subject to relatively little change in salinity or depth but cooled markedly, most probably because of heat loss associated with a partial surface relaxation to climatological sea surface temperatures in a region in which the Gulf Stream was too far to the north. This mixed layer cooling caused the isopycnic layers in the model ventilated subtropical gyre to rise and, surprisingly, to warm. While the experiment was not an attempt to simulate changes in the real Atlantic Ocean, it nevertheless appears from observations that, in recent decades, the mixed layer in nature has undergone a change similar to that exhibited by the model mixed layer. Since it is expected that changes in the ventilated subtropical gyre will be governed largely by changes in the mixed layer in the central North Atlantic, from where the ve...