Dynamics of upwelling on the West Florida Shelf slope

The oligotrophic West Florida shelf (WFS) frequently experiences strong red tides of a toxic dinoflagellate Karenia brevis, which impact the coastal and human health. Nutrients play an important role in shaping these blooms, which come from either land-based river runoff or subsurface waters over the outer shelf. In turn, slope upwelling over the west Florida slope is likely the main process bringing deep ocean nutrients to shelf edge. This process is yet to be well studied. Based on the Regional Ocean Modelling Systems (ROMS), a numerical model has been developed for the eastern Gulf of Mexico including the WFS with a horizontal resolution of 2 km. A two-year (2011-2012) simulation has been conducted and calibrated with available data including temperature, salinity, currents, and volume transport. An analysis of the model results indicates that the upwelling/downwelling along the WFS slope is strongly affected by the Loop Current (LC) transport and position. During the port-to-port mode (LC flowing into the Florida Straits directly), interactions of LC with the shelf slope typically drive a significant northward jet along the slope, which leads to significant downwelling due to the bottom Ekman transport. In contrast, during the extended mode, LC penetrates deep into the Gulf, and it is flowing southward along the southern part of the shelf slope, leading to strong slope upwelling. Other than seasonal cycle, this mechanism appears to be the dominant factor shaping the bottom temperature and nutrients along the west Florida shelf break.

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Primary Presenter: Siddhesh Tirodkar, Florida Atlantic University (stirodkar@fau.edu)

Authors:

Siddhesh Tirodkar, Florida Atlantic University  (stirodkar@fau.edu)

Mingshun Jiang, Florida Atlantic University  (jiangm@fau.edu)