FY 2024

Mesoscale eddies influence coral reef environments in the northwest Gulf of Mexico

McWhorter, J.K., H.L. Roman-Stork, H. Frenzel, M. Johnston, M. Cornec, M. Le Hénaff, and E. Osborne

J. Geophys. Res., 129(6), e2023JC020821, doi: 10.1029/2023JC020821, View open access article at AGU/Wiley (external link) (2024)

Coral reefs globally are experiencing more frequent and severe warming events due to anthropogenic driven climate change. Subtropical reefs experience more seasonal variability than lower latitude reefs making them typically more resilient to climate change. With relatively stable coral cover in comparison to other global coral reefs, Flower Garden Banks National Marine Sanctuary (FGBNMS) in the Gulf of Mexico is a series of 17 reefs and banks located on the continental shelf-edge containing a variety of shallow (0–30 m) and mesophotic (30–150 m) coral reef habitats. Here, we use satellite data products to associate open ocean Argo float profiles with eddy features over FGBNMS to study the shelf-edge reef environment spanning nearly two decades (2003–2022). Satellite data show that FGBNMS is frequently influenced (∼15 days/month) by mesoscale eddies. The upper water column variability (0–25 m) is most influenced by the seasonal mixed layer despite eddy interaction. Subsurface seasonal ranges of temperature and salinity are enhanced or suppressed depending on the influence of eddies in relation to the mixed layer depth. Within the mesophotic zone (0–150 m), the largest range of thermal variability between anticyclonic and cyclonic eddies is between 50 and 150 m upwards of 5°C. However, these observed dynamics will likely change as a result of eddy variability associated with projected warming and Loop Current weakening, leading to increased thermal stress in the future.

Plain Language Summary. Coral reefs globally are threatened by climate change, yet some reefs are less impacted than others, such as coral reef habitats in Flower Garden Banks National Marine Sanctuary (FGBNMS) located in the northwestern Gulf of Mexico. This study demonstrates an exposure to large temperature and salinity ranges across different depths throughout the year which may aid in the resiliency and longevity of this ecosystem. The Gulf of Mexico contains some of the most energetic eddies, or spinning currents, in the world. While these eddies originate in the open ocean, they are mobile features that move onto FGBNMS over the shelf-edge ∼15 days/month, translating open ocean physical and biogeochemical signatures. Here we find that the eddies on FGBNMS show significant alterations to temperature and salinity conditions. Importantly, the physical oceanography driving the eddy field is expected to weaken under climate change, potentially threatening this unique shelf-edge reef system, and subjecting the coral reef habitats to warmer ocean temperatures in the future.