Wintertime Expansion and Contraction of the Terra Nova Bay Polynya

Abstract

A one-dimensional coastal polynya model, forced by data from a near-by automatic weather station, is used to examine wintertime ice concentration fluctuations in the Terra Nova Bay polynya. It has long been believed that the Terra Nova Bay polynya opens in response to strong offshore katabatic wind forcing. This study shows that not only is the sensible heat flux important in controlling fluctuations in polynya extent, but that the longwave heat fluxes is important also. Moreover, this study shows that wind forcing becomes important to the polynya dynamics as an amplification factor acting on the longwave flux term. Together these two terms can explain up to 40% of the observed variance in open water fraction. Some large-amplitude fluctuations in open water fraction at Terra Nova Bay were not well modeled in this study. These anomalies are believed to be related to large-scale changes in the Ross Sea pack ice, which are driven by strong winds blowing off the Ross Ice Shelf. Ice production rates were found to be comparable with historical estimates. To maintain a conversion of Warm Core Water or Low Salinity Shelf Water (S congruent to 34.5PSU) to High Salinity Shelf Water (S congruent to 34.8 PSU) consistent with the observed ice production rate, a transport of approximately I Sv is required at Terra Nova Bay.