Satellite-based empirical models linking river plume dynamics with hypoxic area and volume

Satellite-based empirical models explaining hypoxic area and volume variation were developed for the seasonally hypoxic (O-2 < 2 mg L-1) northern Gulf of Mexico adjacent to the Mississippi River. Annual variations in midsummer hypoxic area and volume were related to Moderate Resolution Imaging Spectroradiometer-derived monthly estimates of river plume area (km(2)) and average, inner shelf chlorophyll a concentration (Chl a, mg m(-3)). River plume area in June was negatively related with midsummer hypoxic area (km(2)) and volume (km(3)), while July inner shelf Chl a was positively related to hypoxic area and volume. Multiple regression models using river plume area and Chl a as independent variables accounted for most of the variability in hypoxic area (R-2=0.92) or volume (R-2=0.89). These models explain more variation in hypoxic area than models using Mississippi River nutrient loads as independent variables. The results here also support a hypothesis that confinement of the river plume to the inner shelf is an important mechanism controlling hypoxia area and volume in this region.