A report on the continental shelf circulation and coastal upwelling

Abstract

The bathymetry and hydrography of the coastal regime of continents are a complex maze which belies their physical description in simple shapes and coherent water masses. Each river outflow, shelf canyon, bay, harbor, and sandbar has its distinct character and depending on a variety of atmospheric conditions, is bordered by a distinct water mass. The shallow beach zone has been a region of intense study which has been led by coastal engineers for several decades. In reviewing the advances in research in coastal oceanography it is heartening to find that a significant body of unifying ideas and models for the deeper continental shelf emerges. This indeed must be inevitable because the dynamic structure of the oceanic water mass is constrained by Newton's laws of high Reynolds number and the second law of thermodynamics of high Peclet number in which the variety of local conditions become hydrodynamically similar. However, such an overview has been a long time coming in the United States because only in the past 10 years have direct observations of continental shelf water motions been made in a manner by which the variability of the hydrodynamic regime on the shelf can be clearly documented. The most significant advance is that coastal oceanographers have begun measuring, describing, and modeling the long‐wave shallow water turbulence on the continental shelf. Past interpretation of sea surface and sea bed drifter statistics and the classical hydrographic file implies that the synoptic continental shelf circulation patterns are a morass; however, a more focused picture emerges from long time series of direct current measurements, closely spaced and frequently sampled hydrographic surveys, and infrared and color satellite imagery. It is found that continental shelf circulation principally varies with the (1) local variations in the atmospheric wind stress and thermohaline forcing on both synoptic and seasonal time scales, (2) eddies and long waves which impinge from the deep sea, and (3) tidal phenomena.