Abstract
Analysis of year-long drifter trajectories and records of simulated surface Lagrangian Coherent Structures (LCSs) have suggested the presence of a resilient Cross-Shelf Transport Barrier (CSTB) on the West Florida Shelf (WFS). The CSTB was conjectured to provide a large degree of isolation, which is consequential for the fueling of red tides on the southern WFS by nutrients possibly released by rivers and canals directly on the region. Here this conjecture is thoroughly tested by identifying LCSs as well as performing tracer advection calculations based on seven-year-long records of surface and subsurface currents produced by a HYbrid-Coordinate Ocean Model (HYCOM) simulation of the Gulf of Mexico (GoM). The identified LCSs suggest that the CSTB extends downward in the water column. The tracer calculations suggest that, while the majority of the nutrients possibly released by rivers and canals directly on the southern WFS are retained within the region for long times, only a small fraction of the nutrients possibly released by rivers outside the WFS reach the southern WFS, mainly accompanying shoreward excursions of the CSTB. These results add importance to the role played by the CSTB in controlling red tide development on the WFS. Implications of the results for the dispersal of pollutants, such as oil, in the GoM are discussed.
Highlights
The toxic dinoflagellate Karenia brevis is present in low concentrations in large areas of the Gulf of Mexico (GoM; Fig. 1), and it sporadically forms blooms anywhere in the GoM (Wilson and Ray, 1956; Geesey and Tester, 1993; Tester and Steidinger, 1997; Dortch et al, 1998; Kusek et al, 1999; Magana et al, 2003)
Discussion in Tampa (Charlotte) Bay o2s6cillate between 100% and no less than 70% (60%). These oscillations conceal a signal with a period of approximately 12 months, and mainly reflect shoreward excursions of the Cross-Shelf Transport Barrier (CSTB)
The discussion is started by considering the possibility of connecting the presence of the CSTB with observed occurrence of West Florida Shelf (WFS) red tides
Summary
The toxic dinoflagellate Karenia brevis is present in low concentrations in large areas of the Gulf of Mexico (GoM; Fig. 1), and it sporadically forms blooms anywhere in the GoM (Wilson and Ray, 1956; Geesey and Tester, 1993; Tester and Steidinger, 1997; Dortch et al, 1998; Kusek et al, 1999; Magana et al, 2003). Of particular relevance for the present work is the hypothesis of Stumpf et al (2008), who argued that, upon reaching the WFS, subsurface nutrients of Mississippi River origin can be transported onshore via upwelling, and fuel red tides. This scenario does not seem to be consistent with the yearround presence of a Cross-Shelf Transport Barrier (CSTB) on the WFS (Yang et al, 1999; Olascoaga et al, 2006). In Olascoaga et al (2006) it was conjectured that the CSTB behaves as a trap for nutrients
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