Investigations into the Seasonal Deep Chlorophyll Maximum in the Western North Atlantic, and its Possible Significance to Regional Food Chain Relationships.

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 micrometers and 0.067 micrometers 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 NO3, NO2, NH3, PO4, SiOH4, oxygen concentration, temperature, and salinity. Parameters were measured as concommitantly 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.