Mobile Bay in the Northern Gulf of Mexico is a shallow (~3 m) and broad (10-30 km) estuary with a deep (12-14 m), relatively narrow (120 m) ship channel along its length, providing an example of a 'channel-shoal' estuary. This type of geomorphology is common in the shallow estuaries of the Gulf of Mexico, where channels may be essential conduits of salt and other materials from deeper coastal waters. This numerical modeling study based on the Regional Ocean Modeling System (ROMS) will investigate the lateral circulation and associated forcing dynamics in this channel-shoal estuary, where the influence of the ship channel is poorly understood. Specifically, this study seeks to answer the question: How does the estuarine bathymetry affect the lateral exchange between the channel and shoals? A mid-bay cross-section was examined using the model to quantify the channel-shoal interaction in this system. The depth-averaged longitudinal saltwater intrusion is strongest in deeper channels and weakest in shallow shoals. The resulting differential advection from the channel to the shoals sets up a strong lateral salinity gradient, which provides a baroclinic driving force that may generate significant lateral circulation in this system. The shallower shoals are expected to limit the amount of lateral baroclinic forcing to the channel-flank transition zone. This study suggests that the lateral scale associated with the transition from channel to shoals, rather than the overall width of the channel-shoal estuary, affects the relative relevance of channel-shoal interaction.

The past ten years has seen a significant increase in freshwater inputs to the Mississippi Sound (MSS), associated with amplified riverine inflows and human managed freshwater diversions. In addition, with the intent of reversing wetland losses, the State of Louisiana has developed plans to invest in new man-made sediment diversion infrastructures that would further amplify these freshwater inputs to the region. As a first step toward assessing how evolving diversion implementations will affect living marine resources of the Mississippi Gulf Coast, the University of Southern Mississippi modeling group has developed a 400 m resolution, 24-layer circulation model of the Mississippi Sound and Bight (msbCOAWST), which utilizes the COAWST modeling system. This model is designed to support the coastal management community, providing the tools and resources needed to better evaluate complex scientific issues and inform resource management decisions. We are currently testing our model domain framework, which has been designed to explicitly include freshwater diversion constructs that affect the estuarine waters of the MS Sound/Bight. Here, we present initial results that demonstrate the utility of our modeling framework, focusing on the unprecedented 2019 freshwater incursions that led to catastrophic impacts on the oyster reefs situated within MS Sound.

Shallow coastal sediments are important for global carbon storage and nutrient cycling, marine infrastructure and navigation, and provide a habitat for diverse communities of burrowing invertebrates (infauna). Extreme storms such as tropical cyclones can dramatically restructure shallow sediment and kill infauna through resuspension and sand deposition from barrier island erosion. Additionally, infaunal activities, including burrowing, tube construction, and feeding on sediment, can impact sediment structure and stability. However, little is known about how infaunal communities recover after hurricanes and how recovering infauna impact sediment stability. We investigated temporal changes to surface sediment physical properties (erodibility, grain size, porosity), bed shear stress, and infaunal community structure at 5m, 12m and 20m depths in the northern Gulf of Mexico following Hurricane Sally (2020). We expected that changes to erodibility immediately after Hurricane Sally would relate mainly to storm-generated changes to grain size and porosity whereas months after Sally, temporal changes to infauna community structure would drive temporal erodibility differences at a given site. We also expected that infaunal impacts to erodibility would be greater in cohesive muds compared to clean sands. Here we present data on temporal changes to sediment and infaunal community structure from sediment cores collected offshore of Alabama 6d before and 10, 40, 85, 162 and 251d after Hurricane Sally. These results will provide insight on how tropical cyclones impact sediment and infaunal community structure on small spatial scales as well as the short and long-term impacts of infaunal community recovery on sediment stability and transport.

Microplastics (< 5 mm) pollution is a growing problem affecting coastal communities, marine ecosystems, aquatic life, and human health. Aquatic biota such as plankton, fishes, and shrimp ingest microplastics that interfere with organ functions, reduce growth, and eventually kill these organisms. Microplastics can also bioaccumulate in humans through the consumption of seafood, possibly leading to oxidative stress and cell damage. Despite the extensive negative impacts, studies on microplastic consequences have been limited due to the lack of large-scale, long-term monitoring and collection of data. The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI) now offers global open access to marine microplastics data on an easily discoverable, public GIS web map and data portal https://www.ncei.noaa.gov/products/microplastics. The objective of this data portal is to provide a repository where microplastics data are aggregated, archived, and served in a user friendly, consistent, and reliable manner. This work contributes to NCEI's efforts towards data integration, harmonization, and interoperability among national and international collaborators for monitoring global marine microplastics. In concert with national and international efforts, NCEI aims to adapt to user needs as contributors to this rapidly evolving science come to a consensus on reporting metrics and sampling methods. Through this data visualization and access portal, researchers and interested groups will be able to access and analyze data that will enable a better understanding of the potential impacts that microplastics may have on human health, marine wildlife, and the blue economy.