Hydrographic and acoustic evidence for enhanced plankton stocks in a small cyclone in the northeastern Gulf of Mexico

Mesoscale eddies (diameters of hundreds of km) have been shown to influence plankton production as well as the distribution of seabirds and marine mammals in the Gulf of Mexico. Smaller circulation features (eddies with diameters of tens of km) may have similar effects. We show that a small, sub-mesoscale cyclone located on the continental shelf and slope in the northeastern Gulf of Mexico during November 1997 was an area of enhanced nutrients, chlorophyll, and acoustic volume backscattering strength (S-v). Nitrate concentrations at mid-depth in the euphotic zone were as high as 2 muM, surface chlorophyll exceeded 1 mug l(-1), and S-v was as much as 15 dB referenced to 1 m(-1) 4pi(-1) greater within this feature than in surrounding waters. Since S-v at 153 kHz is a proxy for the abundance of sound-scattering mesozooplankton and micronekton, we infer that this cyclone was locally enriched in biomass of these organisms. As with mesoscale eddies, smaller cyclones could also function as patches of favorable habitat for higher-trophic-level organisms and their prey. (C) 2003 Elsevier Science Ltd. All rights reserved.