Mechanisms and measurements of generation of stresses in first-year landfast sea ice

Stresses in first-year landfast sea ice was measured by UNIS for the fourth season in Van Mijenfjorden on Svalbard, Norway. Five stress sensors were frozen-in at 15 cm deep in the active layer from end of February until late April 2006. One vertical and one horizontal thermistorstrings logged temperature-profiles, respectively through ice thickness and along the snow/ice surface. Two stress events were identified, one in mid March and one in late March/early April. The peak stresses reached respectively 38.9 kPa and 54.7 kPa. Neither air temperature nor wind can explain these events. An unusual amount of snow isolated the sea ice so that sea ice temperature variations were smaller than what is required for thermal expansion and stress generation. Earlier years air temperature variations have caused stresses up to 200 kPa. However, the thick snow cover did cause flooding of the ice surface in the second part of the winter, and we believe that snow loading coupled to spring tides caused the two stress peaks. A relation is also derived to assess the flooding condition.