Multiple Steady States and Hysteresis off a Boundary Current Leaping across a Gap: Socian Shelf Water Crossover Events

University Of Rhode Island, Kingston RI

Investigators

Abstract

0351518 The problem of a shelf-break current crossing over a strait will to be investigated using theoretical, numerical, and laboratory approaches with the emphasis on understanding the dynamics of such a process. The project will address specific questions: how and under what conditions does crossover occur; what is the character of the transition between the states with and without crossover; what are the characteristics of the crossover events, and what indices and locations can be used to monitor the crossovers. As a prototype of this process, the Scotian Shelf Water (SSW) crossover events occurring in the Northeast Channel, separating Georges Bank from the Scotian Shelf will be considered.. The SSW crossovers, rich in plankton, have important implications for Georges Bank biological productivity. The dynamical process itself is very dramatic and very distinct, but poorly understood. The bathymetry in this area is relatively simple, allowing idealized theoretical representation and finally, a lot of observational data has been recently collected as a part of the U.S.GLOBEC (GLOBal ocean ECosystems) program on Georges Bank, which needs to be analyzed and synthesized. The data come from various sources: multiple large-scale hydrographic surveys, fine-resolution sections, moorings, drifters, sea surface temperature measurements from satellite, wind data from weather buoys, etc. The SSW crossover events in these data are well documented. Preliminary work indicates that the crossovers can be reproduced by varying the intensity of the shelf-break current related to the slope/shelf density difference within a range consistent with realistic annual variability. Broader Impacts: Understanding the causes and variability of the SSW crossovers is critical for the knowledge of basic ecology of the region and successful management of the Georges Bank fisheries. Slight changes in temperature and salinity differences between the shelf and slope water may potentially allow continuous flow of SSW onto the Georges Bank. The hydrographic conditions in this region are known to be linked to the North Atlantic Oscillation (NAO) and the river output from the Gulf of St. Lawrence, and therefore are greatly affected by the global warming and climate change. The proposed project will benefit the educational and research programs at the University of Rhode Island by supporting a graduate student and by allowing the PIs to mentor summer students in the SURFO program. It will also enhance the utilization of a recently acquired equipment in the geophysical fluid dynamics laboratory for active research during this project and through collaboration with colleagues.