The continental shelf, a submerged extension of a continent, serves as a crucial interface where terrestrial, oceanic, and atmospheric influences converge. This unique confluence plays a pivotal role in driving the high biological productivity often observed in continental shelf regions. These productive ecosystems are not only vital for the diverse marine life they support but also have far-reaching implications for the livelihoods of coastal communities, including tourism, fishing, and aquaculture.
However, anthropogenic climate change is poised to bring about profound transformations in the dynamics of continental shelves. Changes in local atmospheric circulation, heat distribution, and evaporative fluxes can disrupt the delicate balance of surface fluxes, horizontal transports, and vertical mixing in these regions. Additionally, alterations in freshwater discharge, whether driven by land management practices, climate-induced rainfall variations, or human-made modifications, can significantly impact shelf dynamics and either mitigate or exacerbate the effects of climate change.
One area where these changes are particularly evident is the Gulf of Mexico, specifically along the west coast of Florida. This region is influenced by a multitude of freshwater sources that transport water from rivers, streams, lakes, and canals into the nearshore areas. This freshwater influx plays a substantial role in shaping the estuarine properties of the West Florida Shelf waters, with effects spreading westward and southward across the shelf.
South Florida, in particular, is undertaking an ambitious endeavor—the Comprehensive Everglades Restoration Plan—to restore the Greater Everglades Ecosystem by reinstating freshwater flows to their pre-drainage levels. While the localized effects of changes in water runoff can be assessed, there remain long-range implications for the inner and mid-shelf regions that require a deeper understanding.
In a collaborative effort between Florida Atlantic University’s Harbor Branch Oceanographic Institute and Florida International University, researchers conducted a study aimed at assessing the potential impacts of climate warming and water management on the dynamics of the West Florida Shelf. They used a high-resolution model with a 1.5-kilometer resolution to evaluate the separate and combined effects of freshwater discharge management and a 1-degree Celsius increase in temperature on the intrusion of the Loop Current onto the West Florida Shelf in the sub-tropical western Atlantic.
The results of this study, published in the journal “Bulletin of Marine Science,” unveiled significant insights into the intricate interactions shaping the West Florida Shelf ecosystem:
- Freshwater Discharge and Climate Warming: In a one-year simulation where a Loop Current and its eddy intruded onto the West Florida Shelf, both increased freshwater discharge and a 1-degree Celsius rise in temperature led to notable changes in the stratification properties of the shelf. Increased freshwater discharge intensified the mixing of shelf waters, favoring the surface intrusion of Loop Current waters. Conversely, a 1-degree Celsius warming intensified shelf water stratification, promoting bottom intrusions. These variations could lead to different oceanographic regimes, potentially impacting the local ecosystem’s response.
- Cold Air Outbreaks: The study also examined how the West Florida Shelf responds to cold air outbreaks, common in the fall and winter months. In a warmer climate, increased stratification due to freshwater discharge at the end of the boreal summer wet season was counteracted by the warmer climate, reducing the potential energy available on the shelf. This reduction limited coastal upwelling, instabilities, and shelf convection.
- Ecological Implications: The West Florida Shelf is intricately connected to various estuarine systems and bays, influencing the baroclinicity of the flow on the shelf. Changes in salinity and nutrient patterns resulting from alterations in freshwater flows have had significant direct and indirect impacts on marine life, including algal blooms, seagrass mortality, fragmentation of seascapes, sponge die-offs, and declines in shrimp catches.
The study underscores the intricate relationship between climate change, freshwater management, and the dynamics of the West Florida Shelf. As climate warming and altered freshwater discharge patterns continue to affect this region, understanding their complex interplay becomes increasingly vital for the conservation and sustainable management of this critical ecosystem. The findings suggest that managing freshwater discharge could serve as a mitigating factor against the adverse effects of climate warming on the West Florida Shelf, ultimately preserving the delicate balance of this unique marine environment.