Project Leader: B. Dzwonkowski (PI), J. Lehrter, and D. Tian

Project Details

Shelf hypoxia is a well-recognized management issue for a growing number of coastal regions (Diaz and Rosenberg 2008) that can alter food web dynamics and biogeochemical cycling, resulting in threats to fisheries, coastal economies, and ecosystem health (Breitburg et al. 2009; Diaz and Rosenberg 2011). While hypoxia is often associated with excess nutrients delivered by freshwater inputs, a number of recent studies have indicated the interannual variability in physical forcing functions are as important (in some cases more important) than nutrient loading. Furthermore, there is limited understanding of the impact of extreme events on dissolved oxygen (DO) dynamics (e.g., tropical storms, marine heatwaves). Importantly, the summer season, when hypoxia is most common, has climatological patterns that present potential opportunities for known physical hypoxia stressors (e.g., bottom water temperature, stratification, upwelling favorable wind) to couple with themselves and/or with extreme events to amplify the properties and processes associated with low DO levels. As a result, understanding the coastal climate where multiple physical stressors can potentially couple to amplify environmental conditions conducive to hypoxia is critical for determining shelf vulnerability to this marine hazard.

While summer hypoxia is regularly monitored on the Texas/Louisiana Shelf in the northern Gulf of Mexico, very little shelf monitoring has been conducted on the Alabama shelf, despite a growing body of evidence that indicates hypoxia is a significant issue in the region. To address the need for improved information on DO conditions east of the Mississippi River Delta, we propose a shelf monitoring program (Theme #5 of the RFP) that directly deals with the issue of hypoxia and its relationships with the coastal climate in Alabama. Understanding the local patterns and trends of physical hypoxia stressors (e.g., water temperature, stratification, wind conditions), represents an important component of the climate system that requires high resolution that is not often accurately represented in large-scale regional assessments of environmental conditions. To this effect, the proposed work will investigate three objectives:

Objective #1 Characterize shelf hypoxia and the associated physical stressors in coastal Alabama

Objective #2 Identify relationships between extreme events, physical stressors, and hypoxia

Objective #3 Determine the behavior of physical hypoxia stressors and their interactions under future climate scenarios

The proposed project will use a combination of existing and new observational data, oceanic and atmospheric reanalysis products, and appropriately down-scaled outputs from global climatological models to conduct statistical and mechanistic analyses. A focal point of the investigation will be centered around a novel observational data set from a long-term mooring site on the Alabama shelf that has been collecting water column hydrographic and current velocity data since late 2004 and bottom DO since 2019. Having already captured 15 summer seasons, with a total of 18 seasons expected by the end of the proposed study period, this mooring site provides an exceptional opportunity to better understand the coastal climate where multiple physical stressors can potentially couple to amplify environmental conditions conducive to hypoxia. Furthermore, the longevity of this site allows for uncommon views of the oceanic state during extreme events, including several hurricane passages as well as marine heatwaves and cold spells. Thus, this existing data in hand can be immediately used to begin addressing the multi-stressor impacts and extreme events on shelf DO dynamics. Another particularly novel aspect of this work will be the application of state-of-art machine learning to appropriately downscaled environmental conditions for future climate scenarios to represent climate change most accurately at the local scale for coastal Alabama. These techniques as well as the use of high-dimensional multi-variate models directly address the RFP’s stated interest in encouraging new approaches to address the complex issues associated with multi-stressor interactions and climate change.

Through exploring multi-stressor impacts on hypoxia and how those multi-stressor relationships are expected to change in future climate scenarios, this proposed project addresses fundamental scientific questions related to a major ecosystem hazard that is of local and globally importance. Results of this study will be disseminated to local, regional, and national agencies charged with monitoring coastal water quality in the Mississippi Bight as well as other regional stakeholders concerned about DO levels. Consequently, the proposed project will provide unique insights into the structure and dynamics of hypoxia in the coastal waters of Alabama, which will have direct implications for understanding water quality, ecosystem management, and regional restoration efforts.