Characterization of sea ice cover, motion and dynamics in Marguerite Bay, Antarctic Peninsula

J. Hyatt^#, R.C. Beardsley^#, and W.B. Owens^#

^#Woods Hole Oceanographic Institution, Department of Physical Oceanography, Woods Hole, MA 02543 jhyatt@whoi.edu

As part of the U.S. SO GLOBEC Southern Ocean Program, data from two automatic weather stations (AWSs) on small islets and upward-looking acoustic Doppler current profilers (ADCPs) and an upward looking sonar (ULS) on sub-surface moorings have been analyzed to produce time series of atmospheric forcing, sea ice thickness, sea ice and ocean velocities, and sea ice momentum balances within Marguerite Bay and at mid-shelf on the central west Antarctic Peninsula continental shelf for the austral winter-spring seasons of 2001 and 2002. Both years had roughly seven months of nearly complete sea ice cover, but ice onset was about two months earlier in 2002 than 2001 mostly due to extremely cold surface air temperatures in Marguerite Bay during May-June 2002. Sea ice draft was quite variable, but generally thickened with time, reaching ~2-3 m by the end of September before thinning. In October, 2002, a polynya was observed at one site within Marguerite Bay that lasted for 4 days.

The sea ice motion and dynamics in Marguerite Bay were analyzed when sea ice draft was greater than 2 m. Wind stress during these periods was predominantly southward and southweastward. Wind stress, sea ice, and near-surface water motion were partially correlated, with sea ice motion greater than water motion. Large wind stress and sea ice and water motions occurred during short energetic events of a few days or shorter; however, the rms wind stress, sea ice, and water velocities were small, about 0.3 N m^-2, 8-16 cm^-1, and 5-7 cm s^-1, respectively. Mean sea ice motion was southward, but quite small, of order 2 cm s^-1, while mean near-surface water motion was not statistically different from zero.

The dominant sea ice momentum balance was between wind and internal ice stresses on time scales of several days and longer, with water stress, Coriolis, and tilt terms playing secondary roles. The mean southward wind stress was balanced, within uncertainty, by the mean northward internal ice stress. The strong and variable internal ice stresses were likely due to the onshore winds, the thickness of the sea ice, and the nearby coastline.

STATUS UPDATE

08/30/10: Revision accepted; editor letter sent to corresponding author.