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Chronicle 1 - Prepared by by Doug Biggs, Ann Jochens, and Matt Howard
The Loop Current and Its Spin
Cycles Define the Range of Oceanographic Habitat for Sperm Whales
in the Gulf of Mexico
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Left to Right: Doug Biggs, Matt
Howard, Ann Jochens |
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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. |
| 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. |
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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... |
| ...using remotely-sensed sea surface height
and/or ocean color (Figures 4... |
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...and
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. |
| 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). |
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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. |
| 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). |
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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). |
