The objective of this paper is to provide an overview of progress by U.S. investigators, during the early 1990's, in our understanding of the physical oceanography of continental shelves. In contrast to previous IUGG review articles on continental shelf physical oceanography [ Allen et al., 1983; Brink, 1987], no attempt is made to give a comprehensive overview of all the research which has been done over the previous four years. Instead, this overview focuses on a few areas where there has been significant progress, as examples of the types of research being done in coastal physical oceanography. For a more general overview of shelf dynamics, see the recent summaries by Huyer [1990] and Brink [1991].
Research in coastal oceanography has historically
been motivated
by our society's desire to both exploit and preserve the resources in
coastal waters. As our dependence and impact on coastal waters has grown
in recent years we are faced with increasingly difficult problems, such
as: declining fish stocks on Georges Bank and elsewhere; disasters such as
the Exxon Valdez oil spill over the Alaskan shelf [ Royer,
et al., 1990]; and the growing number of waste disposal sites and sewage
outfalls in our coastal oceans. Rational and well informed decisions
addressing these problems require a better understanding of the coastal
ocean. A clearer understanding of the coastal environment can, for
example, help minimize the impact of disposal sites and sewage outfalls to
the local environment [e.g., Manning, et al., 1994;
Signell and Butman, 1992].
To limit the scope of this overview and provide some coherence, I have focused on the theme of cross-shelf exchange, i.e., identifying and understanding processes that are important in moving water and associated constituents across continental margins. In recent meetings of the coastal oceanographic community, understanding cross-shelf exchange was identified as a central scientific focus, first by coastal physical oceanographers [ CoPO, 1988] and subsequently by coastal oceanographers from all disciplines [ Brink et al., 1992]. This is not a new problem in coastal oceanography. However, I think the recent emphasis on this problem is motivated by several factors: our relatively poor understanding of the processes that result in cross-shelf exchange; the importance of cross-shelf exchange to a wide variety of biological, chemical and geological processes over the shelf; and the relevance of cross-shelf exchange to societal problems associated with coastal waters. Additionally, recent developments of instrumentation and techniques are providing new insights into cross-shelf exchange. I will focus on three topics of research relating to cross-shelf exchange: exchange between the outer shelf and the open ocean; wind-driven cross-shelf exchange over the middle and inner shelf; and buoyant plumes associated with river discharge onto continental shelves.