Seasonal stratification and tidal current profiles along Ronne Ice Front

Throughout much of the year a coastal polynya along Ronne Ice Front in the southern Weddell Sea is maintained by winds blowing from Ronne Ice Shelf and tidal divergence [Foldvik et al., 2001; Renfrew et al., 2002]. In wintertime, the coastal polynya is the focus of intense heat loss, as relatively warm water is exposed to the cold atmosphere, causing the seawater to cool to its surface freezing point, with further heat loss resulting in sea ice production. Sustained sea ice production is maintained as newly formed sea ice is transported northward away from the polynya by offshore winds. Production rates are 1 or 2 orders of magnitude higher than for the surrounding sea ice, with typically 6.1 % of the entire Weddell Sea ice production focused within the polynya that makes up only 0.013 % of the Weddell Seas area [Renfrew et al., 2002]. The associated High Salinity Shelf Water (HSSW) production will be equally intense within the polynya resulting in convective overturning of the entire underlying water column during winter [Foldvik et al., 2001; Nicholls et al., 2003] and a strong seasonal signal in the water column properties. Any changes in seasonal stratification are likely to significantly affect the tidal current profile in this region [Makinson, 2002]. It is the strongly depth dependent semi-diurnal tidal currents, associated with the proximity of the critical latitude [Foldvik et al., 2001; Foldvik et al., 1990], that are sensitive to these changes. The northern most part of the Ronne Ice Front region lies near the M2 critical latitude (74° 28' 18"S), which can give rise to a thick bottom boundary layer that may occupy the entire water column. Along the ice front, early observations of tidal currents and water column properties were confined to short summer observations and hence no seasonal data was available. However, four moorings with records greater than one year have been successfully recovered from the Ronne Ice Front coastal polynya [Foldvik et al., 2001; Woodgate et al., 1998]. Initial analysis by Makinson and Schröder [2004] has shown that during periods of stratification, the tidal current profile is notably different from those during the winter. The data from these moorings forms the basis of the work presented here and their locations are shown in Figure 1.

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