Mixing in the pycnocline over the western
Antarctic Peninsula shelf during Southern Ocean GLOBEC
Susan L. Howard1,
Laurence Padman1, and Jason Hyatt2
1 Earth
& Space Research, 1910 Fairview Ave. East, Suite
102, Seattle, WA 98102-3620
2 Dept. of
Physical Oceanography, Clark 332, MS #21, Woods Hole Oceanographic Institution, Woods Hole,
MA 02543
The Southern Ocean Global
Ecosystem Dynamics (SO GLOBEC) program studied the continental shelf region in
the vicinity of Marguerite Bay, on the western side of the
Antarctic
Peninsula, to determine the factors that contribute to Antarctic krill survival
over winter. Intrusions of Upper
Circumpolar Deep Water (UCDW) onto the shelf provide much of the nutrient flux
into the region. Here we describe the
small-scale mixing processes that subsequently transport heat, salt and
nutrients from the UCDW up to the surface mixed layer. The study makes use of
CTD and vessel-mounted acoustic Doppler current profiler data collected during
5 research cruises between March and September 2001. The dominant cause of upward turbulent fluxes
appears to be shear-driven mixing associated with near-inertial baroclinic waves excited by wind stress variations. The mean vertical diffusivity associated with
this process is estimated at ~1 x 10-5 m2 s-1,
corresponding to a heat flux into the base of the mixed layer of 1-2 W m-2. Preliminary modeling studies suggest that baroclinicity of diurnal tides might contribute to vertical
mixing near the shelf break, but further studies are needed to confirm
this. A previous suggestion that
double-diffusive convection provides significant heat fluxes in this region is
not supported by our analyses of the bulk properties of the pycnocline:
the area-averaged double-diffusive heat flux is estimated at ~0.2-0.4 W m-2
over the central and inner continental shelf, and ~0.4-0.9 W m-2
over the continental slope.
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