Recent studies indicate that phytoplankton can be significantly enriched in 13C during bloom conditions. This study seeks to confirm this association in shelf and slope waters of the northern Middle Atlantic Bight and Gulf of Maine. High precision carbon isotope ratio measurements will be done on preserved samples from quarterly cruises as well as on laboratory phytoplankton cultures and extracted chlorophyllide a from live phytoplankton. In addition to these primary objectives, initial studies of the utility of the nitrogen and carbon isotopic signatures in analyzing food web structure will be made. Isotopic analysis of selected higher trophic level organisms will be made for this purpose. An element may exist in more than one atomic weight, and these various forms are called isotopes of that element. Although chemically similar, the ratios among the elemental isotopes vary among pools because of fractionation processes associated with chemical and physical transformations. Isotopic signatures have long been used in other areas of earth science, and this study attempts to extend this usefulness into marine ecology. This study examines the hypothesis that variations in productivity are associated with isotopic variations. This is an exciting prospect, in that such a relationship would serve as a useful adjunct to (or even replacement for) current tracer techniques of measuring productivity, as well as serve as a tracer for marine food web studies. The study consists of both laboratory work and field sampling in Georges Bank, a productive fishing ground off the U. S. New England coast.
