The role of the West Florida Shelf topography on the Loop Current system variability

The evolution of the Loop Current (LC) system under the interaction with the complex topography of the Gulf of Mexico (GoM) is examined. Focusing on the eastern GoM, we study the sole effects of the West Florida Shelf (WFS) topography on the LC system variability. We conduct numerical experiments using the free-running Hybrid Coordinate Ocean Model (HYCOM), at 1/25 degrees horizontal resolution and 26 hybrid vertical layers. A simulation with realistic topography (Control run) has been performed over 8 years and we analyze the last 5-year period (2007-2011). Modified topography with a deeper and smoother continental shelf is then introduced and we perform a 5-year simulation over the same study period. In addition, we perform two independent experiments with the same topographic modifications that are initialized from fields during minimum and maximum LC northernmost extension. The results show that in the case of the modified shelf, the LC tends to extend farther into the GoM, with a predominant westward axis tilt, and rarely retracts south of 26 degrees N even after Loop Current Eddy (LCE) shedding events. The results also suggest that although the LC can be in the vicinity of the southwestern tip of the modified WFS, it is not prevented from extending northward, as it usually happens in the simulation with realistic topography. Finally, the evolution of the LC into the GoM is influenced by lower layer processes associated with the bottom topography in the southwestern WFS and western Straits of Florida. More specifically, lower layer intensified/weakened positive potential vorticity signature promotes retracted/extended LC phases.

Automated summary

This study examines the evolution of the Loop Current (LC) system in the Gulf of Mexico under the interaction with the topography, focusing on the effects of the West Florida Shelf (WFS). Numerical experiments show that modified topography allows the LC to extend farther into the Gulf of Mexico, compared to simulations with realistic topography. Lower layer processes associated with the bottom topography in the southwestern WFS and western Straits of Florida play a role in influencing the evolution of the LC.