One-dimensional modeling of vertical
mixing in a seasonally ice-covered, stratified, high-latitude coastal ocean
Hyatt, J., Beardsley, R.C.,
and Owens, W.B.
The PWP (Price et al., 1986)
one-dimensional vertical mixed layer model was adapted for investigation of
mixing beneath an ice-covered ocean. Simulations using an idealized storm
forcing of a stratification representative of winter on the western Antarctic Peninsula (wAP) shelf revealed the
relative roles of wind mixing and convection due to brine rejection in vertical
mixing. When reasonable ice-ocean drag
coefficients were used (0.015), the presence of ice did not greatly change the
modeled response of the water column when compared with the open water
case. Shear mixing driven by the initial
wind event, not the subsequent shear associated with inertial oscillations,
caused the mixing and subsequent deepening of the mixed layer.
The model results indicate that
the combined effects of shear and static instability can be significant over
short time scales. The model forced by observed
atmospheric and ice conditions on the wAP shelf
produces large vertical fluxes for short periods, a ~385 W m-2
one-day averaged heat flux across the base of the mixed layer during a storm
event. However, when averaged over the
entire 6-day simulation, the flux reduces to a more modest 79 W/m2
across the base of the mixed layer. Making the rough assumption of one storm event per month with the
remainder of the month having a weak flux (17 W m-2) yields a
monthly average flux of 29 W m-2 across the base of the mixed layer.
The small (17 W/m2) fluxes
estimated during the period of inertial oscillations following the storm event
are consistent with the estimate made in Howard et al. (2004) of ~5 W m-2
over the sharp pycnocline during a 4-day period of
inertial oscillations in August, 2001. Furthermore, the results support the notion proposed in Howard et
al. (2004) that intermittent but relatively energetic events may be the dominant
contributors to mean turbulent diapycnal fluxes.
STATUS UPDATE
07/20/09: Editor letter and
reviews #1 and 2 sent to corresponding author.