Biological and isotopic changes in coastal waters induced by Hurricane Gordon

Fogel, Marilyn L., Carmen Aguilar, Russell Cuhel, David J. Hollander, Joan D. Willey, Hans W. Paerl

Limnol. Oceanogr., 44(6), 1999, 1359-1369 | DOI: 10.4319/lo.1999.44.6.1359

ABSTRACT: The effects of a major storm event (Hurricane Gordon) on the biogeochemistry of Atlantic coastal and Gulf Stream waters were investigated during a research cruise in November 1994. Prestorm, NH4+, NO3+, and PO4-3 concentrations were consistently well below 1 mM, whereas after the storm, nutrient concentrations were higher in the surface-water samples: >2 µM, in some instances. Primary and secondary (bacterial) production were stimulated by factors of 5 and 2, respectively, up to 4 d following the storm. Bioassay experiments showed that additions of inorganic N stimulated chlorophyll a (Chl a) concentrations, 14CO2 fixation, and stable isotope fractionations both before and after the storm, but the addition of phosphate had a greater impact in post-storm experiments. The δ15n of particulate nitrogen (PN) varied from +5 to +1.5‰ before Gordon, then afterward attained a consistent value of +3.0‰. Sedimentary organic δ15n values were similar to water-column organic N, and the δ15n of dissolved NH4+ from surface sediments (+4.0‰) almost matched the δ15n of water-column particulates. These results indicate that storm-generated winds mixed sediments along with dissolved nutrients into surface waters, which supported a rapid increase in water-column primary production.

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