Boundary processes in the nutrient-bearing stratum of the North Atlantic

Abstract

Three parallel lines of work were initiated in the new three-year cycle of this grant which begun in March 1988. One deals with the role of the continental margins in the circulation and mass balance of the nutrient bearing stratum'' of the North Atlantic, another aims at elucidating the physics of cross-shelf exchange processes, and the object of the third one is analysis and interpretation of observations taken in the SEEP I and II and MASAR experiments. The major effort of the PI was devoted to the role of the Gulf Stream in raising nutrient-rich upper thermocline fluid from the Sargasso Sea to a near-surface band on the shore-side of the Stream, and transporting it northeastward into the northern North Atlantic. The first accomplishment was a theoretical model quantifying western boundary upwelling'' and linking it to the energy dissipation occurring in such boundary currents as the Gulf Stream. Building upon the theoretical ideas, a calculation of nutrient transport by the Gulf Stream was undertaken at a succession of sections from the Florida Straits to the Grand Banks. The calculations were carried out by Jose Pelegri, a mature-age graduate student who joined the project in December 1988. First, the northeastward transportmore » of nutrients by the Stream more than doubles between the Florida Straits and Cape Hatteras. This verifies the idea that the Stream collects a large inflow from the upper thermocline, the nutrient bearing stratum. Second, the core of the alongstream Reynolds flux (velocity times concentration) lies at a depth of only about 400 m. This again conforms to the notion that waters from the upper thermocline rise under the Stream and release their potential energy. Also, of course, they come into closer contact with the near surface layers. 6 refs.« less