Biological and isotopic changes in coastal waters induced by Hurricane Gordon

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 μM, 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.