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.