Associations between chlorophyll and wind forcing in the Gulf of Mexico derived from satellite observations

Abstract

The Gulf of Mexico supports many industries that rely on its natural resources. Primary production is required to sustain fish populations and contributes to ocean carbon exchange. Ocean color satellites make it possible to observe large geographic areas; however, an individual sensor has limited coverage. The GlobColour project merges observations from multiple satellites into a single product. The purpose of this study is to use GlobColour and QuikSCAT to investigate the seasonal and non-seasonal associations between chlorophyll and wind from 2000-2008 in the Gulf of Mexico. An overview of the Gulf of Mexico’s physical setting, circulation, and main features is presented. The Gulf is divided into: Interior Basin, West Florida Shelf, Louisiana-Texas Shelf, Tamaulipas-Veracruz Shelf, Bay of Campeche, and Campeche Bank. Phytoplankton biomass is discussed in the context of nutrient-transport mechanisms including coastal upwelling, Ekman pumping, horizontal advection, and vertical turbulent mixing. Seasonal associations are evaluated between chlorophyll and wind using Empirical Orthogonal Functions and Singular Value Decomposition. Chlorophyll has strong seasonal variability over the shelves. The interior variability of chlorophyll and wind speed is in-phase with annual periodicity, increasing in winter and decreasing in summer. Strong winter winds increase the upward turbulent transport of nutrients into the mixed layer. The northern chlorophyll variability has a dipole with increased anomalies over the Western Shelf and decreased anomalies around the Mississippi mouth; associated with intensified easterly winds. Non-seasonal anomalies of chlorophyll and wind are similarly investigated. Increases in wind speed are associated with chlorophyll increases over the Campeche Bank, Bay of Campeche, and West Florida Shelf; the mechanism is upward entrainment of nutrients by turbulent mixing. Northerly winds are associated with coastal upwelling in the Bay of Campeche, offshore advection in the west, and a chlorophyll dipole across the Mississippi mouth. The non-seasonal coupled patterns are predominantly intraseasonal and spatially coherent with interannual modulations. This study is the first to apply a merged ocean color product to research in the Gulf of Mexico. Overall, this project provides baseline information on the seasonal and non-seasonal variability of chlorophyll and winds, identifies statistical associations, and proposes dynamical mechanisms.