Sponsor: National Science Foundation
Woods Hole Oceanographic Institution
September 2009 – August 2012
The ocean region near Cape Hatteras has long been the focus of scientific interest. This region is the terminus of a lengthy shelf current that originates in the Arctic region. Recent evidence indicates that a large fraction of the transport of this shelf current is contained within a jet, which flows over the outer shelf and upper slope and is associated with the shelfbreak front. The shelfbreak jet can contain a significant portion of the fresh water carried towards Cape Hatteras. The maximum in the surface chlorophyll field frequently seen over the outer shelf and upper slope in satellite-derived images further suggests that the shelfbreak current may also encompass a large transport of chlorophyll and organic carbon resulting from shelf production. Recent studies have revealed that the shelfbreak jet is diverted offshore and essentially disappears north of Cape Hatteras, with much of its transport entrained into the Gulf Stream. This offshore loss of shelf water clearly has a significant impact on the balances of fresh water, heat and carbon within the North American coastal system. Dynamics responsible for the offshore diversion, and eventual disappearance, of the shelfbreak jet are currently not well understood. It is clear, however, that a number of processes are involved. These include the interaction of the shelfbreak and Gulf Stream fronts, the narrowing of the shelf cross-section approaching Cape Hatteras, and events of strong wind-forcing and surface heat exchange common to the Cape Hatteras region. We propose a focused study aimed at better understanding these processes and the attendant loss of shelf water to the deep ocean. This will be a coupled data analysis and modeling study. The data analysis component will incorporate measurements from three large-scale field programs as well as sea surface height and temperature fields derived from satellite-borne instruments. The analysis of these data will provide insight into the processes influencing the transport and offshore diversion of the shelfbreak jet, and will be used to assess and refine the model’s performance in the Cape Hatteras region. The model will, in turn, be used to examine, in much finer spatial and temporal detail than possible with actual measurements, the dynamics of processes affecting shelf water flow and shelf water loss north of Cape Hatteras. We believe that our study will not only lead to a better understanding of the dynamics of shelf water loss north of Cape Hatteras, but will further the understanding of similar regions where a shelf current is in proximity with a offshore boundary current.