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

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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 <22.5°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 moles · m−2 · sec−1 across the 42 m isobath and 30 moles · 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.

Document Type: Research Article


Publication date: November 1, 1984

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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