Sperm Whale Seismic Study (SWSS)

Chronicle 1

Special Reports from the SWSS Scientists

Prepared by Doug Biggs
                    Matt Howard
                    Ann Jochens


 

Left to Right: Doug Biggs, Matt Howard, Ann Jochens

The Loop Current and Its Spin Cycles Define the Range of Oceanographic Habitat for Sperm Whales in the Gulf of Mexico.

Figure 1

The Loop Current is the inflow of warm, Caribbean surface water that enters the Gulf of Mexico through the Yucatan Channel into the eastern Gulf, and then exist through the Straits of Florida (Figure 1). This conveyor carries tropical water, and the pelagic juveniles and larvae of Caribbean organisms that ride along in it, northward into the Gulf and then eastward to the Florida Keys and to the Atlantic coast of Florida.
 

Figure 2

When the Loop Current extends northward, it may become unstable and shed a warm-core, or anticyclonic Loop Current Eddy (Figure 2). As we'll explain below, these eddy separation events and the "spin cycles" that result then create a diverse range of oceanographic habitat in this subtropical ocean, from ocean deserts to ocean oases.

Figure 3

Oceanographers at Texas A&M University, in cooperation with our colleagues at the University of Colorado and at the University of South Florida, use both sea-truth (ship gathered) data and remote-sensing from earth orbit to track Loop Current eddy activity. We can see the warm Caribbean inflow using remotely-sensed sea surface temperature (Figure 3) or...

Figure 4

...using remotely-sensed sea surface height and/or ocean color (Figures 4...

Figure 5

The SSH maps and ocean color maps are compiled and posted in near-real-time to websites hosted by the University of Colorado and the University of South Florida.





Figure 6

During oceanographic cruises to put radio tags on sperm whales, like R/V Gyre cruise 05G09 that we're currently fielding 3-30 June, we email these near-real-time remotely-sensed maps to the SWSS scientists at sea (Figure 6).




Figure 7

These remotely-sensed maps allow the field team to vary their survey for sperm whales among the various habitats that are created by the eddy separation cycle (Figure 7). They survey along the edges of LC eddies, as well as in the confluence regions where counter-rotating deepwater eddy pairs entrain coastal water and carry this coastal water offshelf, to determine how sperm whales vary in abundance between the warm-core (anticyclonic) eddies and the counter-rotating cold-core (cyclonic) eddies.

Figure 8

Both types of eddies are the ocean-equivalent of storm systems in the atmosphere. The warm-core eddies are convergence regions, where surface waters are pushed down into eddy interior, and the cold-core eddies are divergence regions, where ocean midwater upwells to the surface (Figure 8).



Figure 9

These opposite processes create ocean desert conditions in surface waters of the interior of the anticyclones, and ocean oases in  surface waters of the interior of the cyclones. The upwelled nutrients in the interior of the cyclones stimulate the growth of more abundant and shallower stocks of plant plankton, while downwelling surface water in the anticyclones pushes the nutricline very deep, to limit plant plankton growth there (Figure 9).