EXCHANGE OF PHYTOPLANKTON ACROSS THE CONTINENTAL SHELF-SLOPE BOUNDARYOF THE MIDDLE ATLANTIC BIGHT DURING SPRING-1988

A moored array of current meters, transmissometers and fluorometers wa s deployed off the Delmarva Peninsula, United States, from 8 February to 9 June 1988 to measure the exchange of particles, phytoplankton and water between the continental shelf and the slope sea. The measuremen ts were made at the 90-m isobath and near the shelf-slope front, which is the natural physical boundary between the shelf- and slope-water. The highest standing stocks of phytoplankton (>4 mg Chl alpha l(-1)) o ccurred during April and May directly above the shelf-slope front. Alt hough the shelf-slope front and associated phytoplankton populations m ade large cross-shelf excursions (>40 km), the vertically averaged adv ective transport of phytoplankton was onshore at the 90-m isobath. Com pared with the estimated primary production on the inner shelf, the ad vective transport across the 90-m isobath was -2.60% +/- 5.52% of the spring production, with the negative values indicating import. These c alculations suggest that primary production occurring landward of the 90-m isobath is not exported laterally, as phytoplankton or phytodetri tus, to the ocean basin. This places a limit on the possible export fr om the shelf, but does not exclude shelf export because roughly half t he volume of shelf water from Cape Cod to Cape Hatteras lies in a thin surface wedge outside the 100-m isobath [WRIGHT and PARKER (1976) Lim nology and Oceanography, 21, 563-571]. Carbon and nitrogen budgets of the Middle Atlantic Bight should acknowledge the limited exchange of p hytoplankton between the inner and outer portions of the shelf.