The efficiency of shelf/basin exchange (SBE) in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography. Numerical model calculations suggest that upwelling-favorable winds generate very little SBE so long as the ice edge remains shoreward of the shelf break, but an abrupt onset of shelf-break upwelling takes place when the ice edge retreats beyond the shelf break. A climatology (1968--2000) of ice conditions from the Canadian Shelf of the Beaufort Sea shows large interannual variability in ice edge extent and duration of ice-free conditions in summer. Similarly, available hydrographic data reflect a corresponding variability in water mass properties. Under scenarios of climate warming associated with greenhouse gas build-up, both the extent and duration of summer melt-back are predicted to increase, and this may have dramatic impacts on SBE and biological productivity.