Title

The formation and evolution of Tortugas eddies in the southern Straits of Florida and Gulf of Mexico

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Meteorology and Physical Oceanography

First Committee Member

Thomas N. Lee, Committee Chair

Abstract

Large cyclonic eddies on the northern edge of the Florida Current are the dominant mesoscale features within the southern Straits of Florida. These eddies, which remain stationary for months near the Dry Tortugas, are fundamental to the retention of fish larvae and provide a mechanism for the advection of pollutants into the Florida Keys National Marine Sanctuary. Observations and model results presented herein demonstrate a strong relationship between the generation of anticyclonic rings from the Gulf of Mexico Loop Current and the evolution of cyclonic Tortugas eddies in the southern Straits of Florida. It is proposed that Tortugas eddies evolve from cyclonic Loop Current frontal eddies which are formed on the western limb of the Loop Current, propagate along the boundary of the current, and become stationary near the Dry Tortugas. In several observed cases, the eddies remain stationary near the Dry Tortugas until they are impacted by an approaching Loop Current frontal eddy. Simulations using a high resolution numerical model indicate that the collision between a Loop Current frontal eddy and a stationary Tortugas eddy typically results in eddy coalescence and ejection of a smaller vortex which propagates through the Straits of Florida. The length of time an eddy spends near the Dry Tortugas is increased when the Loop Current sheds an anticyclonic ring. The ring-shedding process forces the unstable growth and slowed propagation of cyclonic Loop Current frontal eddies and hence a delay in the downstream propagation of the Tortugas eddy.Model frontal eddies were seeded with synthetic surface drifters to investigate the retention characteristics of the eddies throughout their life cycle. Simulations indicate that the eddies retain surface particles despite the severe deformation associated with eddy collisions. Drifters launched within the stronger of two colliding eddies tended to remain concentrated within the seeded eddy while those launched within weaker eddies were redistributed along the features' periphery due to the shearing experienced by the weak eddy. The results suggest an additional intermittent branch in the recruitment pathways previously identified within the Straits of Florida.

Keywords

Physical Oceanography

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9905031