Atmospheric Cyclone Driven Off Shelf and Off Continental Margin Oceanic Mass Flux Events in the Mid-Atlantic Bight U.S.A.

Abstract

The movement of sediment across the continental margins of the United States (U.S.) has been studied by numerous investigators over the past four decades. The classic, comprehensive review of the state of understanding was first provided by Smith (1977). Over that period, there have been several mid-latitude field programs studying the flux of momentum and materials across continental margins staged on both the east and west coasts of the United States. We will consider a data set that has been sitting idle for several decades but is intriguing as it couples atmospheric cyclone passages in the U.S. Eastern Atlantic Continental Margin, Middle-Atlantic Bight, to continental margin offshore fluxes of sediments; an overlooked and difficult to measure phenomena. Along the mid-latitude eastern seaboard of the U.S., there have been three large scale efforts to observe processes related to the flux of momentum and mass across the continental margin covering the region from Cape Cod, Massachusetts to Cape Hatteras, North Carolina. The first two studies were called the Shelf Edge Exchange Program, aka, SEEP I & II. SEEP I was staged between the New York Bight and southern Connecticut and is described by Walsh et al. (1988). SEEP II occurred offshore of the Delmarva Peninsula and is described by Biscaye et al. (1994). The Ocean Margins Program, aka the OMP, the third such effort, was staged between Chesapeake Bay, Virginia and Cape Hatteras, North Carolina and is described by Verity et al. (2002). All three field programs were sponsored by the U.S. Department of Energy. Traditionally there have been two schools of thought regarding the flux of materials on continental margins. One is the hypothesis that there is continual mass transport driven by costal oceanic currents and waves. The second purports that highly energetic events dominate the mass transport time series but offers scant observations to support that hypothesis. We investigate oceanic current and wave data, and cleverly designed sediment trap data, collected on the continental margin of the Middle Atlantic Bight and determine that the mechanisms associated with large accumulations of Lead 210 or 210_Pb, which is derived from the atmosphere, were delivered via an offshore directed flux of sediments. We show that lateral fluxes of sediments which occurred during the passages of high energy atmospheric cyclones were responsible for mechanically driving the across-continental fluxes of sediments.