Elevated N* in the Western Sargasso Sea: Local or Non-Local Origin?

Bermuda Institute Of Ocean Sciences (Bios), Inc., St. George'S

Investigators

Abstract

ABSTRACT OCE-0082166 Researchers at the Bermuda Biological Station for Research hypothesize that there is a supplementary source of fixed nitrogen to the subtropical thermocline of western Sargasso Sea in the form of organic N species laterally advected into the upper ocean of the region from distant sources via the Florida Current and Gulf Stream. Subsequent mineralization of this organic material is needed to yield nitrogen:phosphorous ratios consistent with present geochemical estimates than those expected based on direct observation of local N2 fixation rates in the region. In the source regions in the Caribbean and Tropical Atlantic, directly evaluated biological measurements of nitrogen fixing rates have been described as being more vigorous than that observed in the western North Atlantic. Further, the proposed spatial field measurements are expected to reveal the physical mixing processes responsible for this transport into the subtropical gyre. The index parameters N*and a derived quantity, ProN*, will be used to indicate the degree to which the observed dissolved inorganic nitrate concentration is in excess of that expected from the remineralization of phosphate at Redfield stoichiometries. The field program of spatial sampling within the Caribbean, along the western boundary current and in the western Sargasso will be examined against the temporal variability at the Bermuda Atlantic Time-series Station (BATS).