Turbulence and Prey Field Properties of Gulf Stream Frontal Eddies on the Shelf Break

Louis St. Laurent, Physical Oceanography


Funded Project 2009:

Numerous studies have suggested that the feeding efficiencies of zooplankton and fish are enhanced in regions of active turbulence. Larger predators can exploit these turbulent patches, as their prey is often congregated at these locations. Thus, regions of enhanced turbulence are often associated with sites of heightened biological activity. Top marine predators, such as beaked whales, dolphins, and porpoises, are particularly adept at targeting prey in such regions. Studies aimed at understanding the behaviors of these high-trophic level animals are often tied to surveys of their prey field, consisting of the mid-trophic level nekton that themselves feed on zooplankton. It is through an upward trophic level cascade that the turbulence properties of the ocean influence the behaviors of marine predators.

One environment well suited for turbulent enhancement of the marine predator prey field is Gulf Stream frontal eddies on the Mid-Atlantic Bight. The circulation associated with such eddies favors both the flux of nutrients into the euphotic zone of the continental shelf, as well as turbulence production by enhanced thermohaline and shear fine-structure. Colleagues at the Duke Marine Lab have been surveying the marine mammal activities southwest of Cape Lookout, and find that the presence of frontal eddies significantly influences animal behaviors. It is hypothesized that these behavioral changes are the result of changes in the prey field, triggered by the influence of turbulence being supported by frontal eddy processes.

We propose to run a collaborative two-week study with colleagues at Duke Marine Lab to survey turbulence characteristics of the marine predator prey field during a Gulf Stream frontal eddy event. The new WHOI turbulence glider will be used to survey the upper-ocean hydrographic and microstructure variables in the Cape Lookout region of the Mid-Atlantic Bight. The fieldwork will be supported by the Duke Marine Lab using their coastal vessel, the R/V Susan Hudson. Data collected during this study will be used to explore the relation between turbulence and the prey field. In addition, two students will incorporate the data into their graduate thesis work.