Biological and isotopic changes in coastal waters induced by Hurricane Gordon

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 1991. Prestorm, NH4+, NO3-, and PO4-3 concentrations were consistently well below 1 mu M, whereas after the storm, nutrient concentrations were higher in the surface-water samples: >2 mu M, 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, (CO2)-C-14 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 delta(15)N of particulate nitrogen (PN) varied from +5 to +1.5 parts per thousand before Gordon, then afterward attained a consistent value of +3.0 parts per thousand. Sedimentary organic delta(15)N values were similar to water-column organic N, and the delta(15)N Of dissolved NH4+ from surface sediments (+4.0 parts per thousand) almost matched the delta(15)N 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.