The effect of summertime shelf break upwelling on nutrient flux in southeastern United States continental shelf waters

Gulf Stream-induced upwelling at the shelf break of the South Atlantic Bight (SAB) presents water which, in summer, can intrude onto the continental shelf. In July 1979, an XBT survey of the continental shelf revealed such an intrusion of cold water off St. Augustine, Florida. From weekly mappings, it was determined that Gulf Stream water \u3c22.5°C covered 3280 km2 and occupied 38 km3 shoreward of the 42 m isobath. Using temperature and nitrate distributions and the T°C:NO3 relationship, we determined that 3200 metric tons of nitrate-nitrogen were advected into the study area. Net nitrate-nitrogen fluxes were 32 μmoles · m−2 · sec−1 across the 42 m isobath and 30 μmoles · m−2 · sec−1 across the 30 m isobath.The advection of nitrate-enriched water into the photic zone caused a dramatic increase in phytoplankton biomass. The decreasing nitrate concentrations correlated with chlorophyll increases indicating phytoplankton production was mainly at the expense of nitrate advected into the area. Prior to the intrusion, production was likely supported by regenerated nutrients.Summertime intrusions supply an estimated 2.9 × 104 mtons NO3-N · yr−1 to the middle shelf area of the southern SAB and are thus a major source of nitrogen to that area

Video systems for in situ studies of zooplankton

A variety of survey instruments and systems designed for measuring the behavior of individual zooplankton have been built around video technology. Systems designed for studying behavior are already producing remarkable observations of biological interactions in situ. If the survey tools under development achieve their potential, they will surpass the spatial and temporal resolution of conventional sampling methods, reduce the amount of human effort required for data processing, and also collect taxonomic information that is not available from acoustic devices or the Optical Plankton Counter. This paper (i) describes a variety of video systems for studying zoo plankton in situ; (ii) discusses common design considerations and technical challenges; and (iii) compares the present and future capabilities of video devices with other methods of studying zooplankton in situ