| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Woods Hole Oceanographic Institution October, 1977 In many marine environments accumulations of chlorophyll have been reported to occur at or below depths to which 1% of ambient light penetrates. The phenomenon has been called the Deep Chlorophyll Maximum (DCM). On occasion zooplankton have been observed to be suggestively associated with a DCM. In order to determine, to what extent and under what circumstances, the DCM represents a significant food resource, data were obtained from vertically stratified net tows (both 0.333 μm and 0.067 μm mesh) and water bottle casts taken on eight cruises in the western North Atlantic between November 1973 and August 1976. Parameters measured included: zooplankton biomass, zooplankton functional group abundance, phytoplankton species abundance, chlorophyll concentration, ATP concentration, particulate nitrogen concentration, 14C fixation, biological macro-nutrients (N03, NO2, NH3, P04, Si(OH)4), oxygen concentration, temperature, and salinity. Parameters were measured as concommitanty as possible. Sampling was conducted in the Sargasso Sea, in Gulf Stream cold core rings, and in the Slope Water. Results obtained bear upon three major ecological problems: (a) the evolution of the biological community in a Gulf Stream cold core ring; (b) the sense in which the Gulf Stream represents an ecological discontinuity; and (c) the significance of the DCM as a locus for trophic activity. Zooplankton biomass in the upper 800 m of four Gulf Stream cold core rings significantly exceeded that in the Northern Sargasso Sea. The center of its vertical distribution was uniquely deep. Such a distribution may result in reduced ecological efficiency and increase the flux of organic matter to the deep sea. The phytoplankton assemblage of a cold core ring was significantly different from that of both the Slope Water and the Northern Sargasso Sea many months after ring formation. Certain species ...
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