The relationship between atmospheric teleconnections and hypoxia in the Northern Gulf of America

Abstract The northern Gulf of America (nGoA, formerly Gulf of Mexico) hypoxic zone is primarily driven by the timing and magnitude of freshwater and nutrient loading from the Mississippi and Atchafalaya rivers. However, the effects of the physical forcings of climate and weather are less well known. Global teleconnections, including the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Pacific/North American Pattern (PNA), and El Niño/La Niña Southern Oscillation (ENSO), are known to affect temperature, precipitation, storm tracks, and inland flooding, which indirectly influence hypoxia development and its persistence. This study examines the role of these teleconnections in the size and severity of the nGoA hypoxic zone, as well as their influence over important factors affecting hypoxia, such as shelf sea surface temperature (SST) and chlorophyll-a concentration, and Mississippi River discharge. The results show that hypoxia metrics are largely independent of teleconnection indices across all seasons because the overall effect is dampened by other confounding factors affecting hypoxia development. However, a clear pathway is revealed by which spring PNA creates conditions favorable for summertime hypoxia development where teleconnection indices are significantly correlated with Mississippi discharge. For instance, spring PNA (winter ENSO) is associated with spring (winter) discharge. Because spring discharge is in turn significantly correlated with summer chlorophyll-a concentrations, this research demonstrates that this pathway promotes conditions favorable for summertime hypoxia development. The extensive geographic footprint of the Mississippi River watershed, as well as significant lags present between the timing of the discharge maxima and hypoxia development, likely lead to countervailing and offsetting intra-basin teleconnection responses that dampen the overall relationships. These findings are useful for analysis of physical controls on nGoA hypoxia dynamics, as well as for assessment of hypoxia in other river-dominated coastal regions with large watersheds.