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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L18610, doi:10.1029/2005GL023716, 2005

Hurricane-forced upwelling and chlorophyll a enhancement within cold-core cyclones in the Gulf of Mexico

Nan D. Walker

Department of Oceanography and Coastal Sciences/Coastal Studies Institute Earth Scan Laboratory, Louisiana State University, Baton Rouge, Louisiana, USA


Robert R. Leben

Colorado Center for Astrodynamics Research, University of Colorado, Boulder, Colorado, USA


Shreekanth Balasubramanian

Coastal Studies Institute Earth Scan Laboratory, Louisiana State University, Baton Rouge, Louisiana, USA


Abstract

Clear skies, subsequent to Hurricane Ivan's passage across the Gulf of Mexico in September 2004, provided a unique opportunity to investigate upper ocean responses to a major hurricane. Oceanic cyclonic circulation was rapidly intensified by the hurricane's wind field (59–62 m s−1), maximizing upwelling and surface cooling (3–7°C) in two large areas along Ivan's track. Upward isothermal displacements of 50–65 m, computed from wind stress and sea surface height changes, caused rapid ventilation of thermoclines and nutriclines, leading to phytoplankton blooms with peak concentrations 3–4 days later. Wind speed changes along Ivan's track demonstrated that the cool waters (20–26°C) provided immediate negative feedback to the hurricane's intensity. Although our study focused on a relatively small ocean area, it revealed that mesoscale cyclones, in addition to warm anticyclones, may play an important role in producing along-track hurricane intensity changes.

Received 8 June 2005; accepted 24 August 2005; published 30 September 2005.

Index Terms: 4504 Oceanography: Physical: Air/sea interactions (0312, 3339); 4520 Oceanography: Physical: Eddies and mesoscale processes; 4855 Oceanography: Biological and Chemical: Phytoplankton; 4273 Oceanography: General: Physical and biogeochemical interactions.

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Citation: Walker, N. D., R. R. Leben, and S. Balasubramanian (2005), Hurricane-forced upwelling and chlorophyll a enhancement within cold-core cyclones in the Gulf of Mexico, Geophys. Res. Lett., 32, L18610, doi:10.1029/2005GL023716.