Abstract
The exchange of coastal waters between the Mississippi Sound (MSS), Mobile Bay, and Mississippi Bight is an important pathway for oil and pollutants into coastal ecosystems. This study investigated an event of strong and persistent inflow of shelf waters into MSS and Mobile Bay during October 2015 by combining in situ measurements, satellite ocean color data, and ocean model predictions. Navy Coastal Ocean Model predicted high-salinity shelf waters continuously flowing into the estuarine system and forecasted low-salinity waters trapped inside the estuaries which did not flush out until the passage of tropical cyclone Patricia’s remnants in late October. The October 2015 chlorophyll-a anomaly was significantly low inside and outside the MSS for the 2003 to 2015 time series. Similar low-chlorophyll-a anomalies were only seen in 2003. The October 2015 mean in situ salinities were up to 8 psu higher than mean from 2007 to 2015, and some estuarine stations showed persistent salinities above 30 psu for almost a month in agreement with model predictions. October 2015 was associated with low fall seasonal discharge, typical of fall season, and wind which was persistently out of the east to southeast [45–180]°. These persistent wind conditions were linked to the observed anomalous conditions.
Highlights
The CONsortium for oil spill exposure pathways in COastal River Dominated Ecosystems (CONCORDE) studies the ecosystem dynamics and characterization of the complex fourdimensional physical, geochemical, and bio-optical fields in the Mississippi Bight influenced by pulsed river discharge
A key question addressed by CONCORDE is: Despite the fluvial input into the Mississippi Sound (MSS) and Mobile Bay [Fig. 1(a)], how can oil and other pollutants enter the Sound and Bay from the shelf and reach the coastal mainland, as it did during the Deepwater Horizon (DWH)/Macondo Well oil spill?1 This study focuses on a particular set of meteorological events that resulted in shelf waters being forced into the MSS, and so provides a scenario where an offshore oil spill or other toxic events, could affect the MSS and coastal mainland
We analyzed the available data from different sources together to understand the dynamics of transport of shelf waters into the estuarine system
Summary
The CONsortium for oil spill exposure pathways in COastal River Dominated Ecosystems (CONCORDE) studies the ecosystem dynamics and characterization of the complex fourdimensional physical, geochemical, and bio-optical fields in the Mississippi Bight influenced by pulsed river discharge. A prolonged inflow of saline offshore waters into the MSS and Mobile Bay occurred through the barrier island passes This event lasted until the passage of Patricia’s remnants and subsequent frontal systems over the region and was atypical in its extended duration of more than 7 days as well as in intensity. The goal is to combine ocean model forecasting products and in situ coastal ocean measurements with ocean color satellite imagery to understand the mechanisms that bring offshore saltier waters into the MSS and Mobile Bay for extended periods These mechanisms including coastal ocean circulation, river discharge, and meteorological forcing will be examined to improve the understanding of inflow and intrusion of shelf waters into the estuaries which could potentially bring offshore sources of oil and toxins into coastal systems
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