THE LIFE STORY OF A 1ST-YEAR SEA-ICE RIDGE

Field data are described and analyzed from all-winter monitoring of th e structure and temperature of one sea ice ridge in the northern Balti c Sea in the winter of 1991. The ridge aged to 3.5 months and experien ced substantial structural evolution: the consolidated layer grew to 1 m, average porosity decreased from 0.28 to 0.18, keel thickness decre ased by 1 m, and the ridge geometry became smoother. The porosity decr eased due to freezing and showed a persistent minimum of 0.20-0.23 in the midkeel region; the void distribution changed due to packing rearr angements of ice blocks. Ice volume changed due to thermodynamic growt h and decay. Within the sail and consolidated layer the heat flow was mainly vertical varying with time according to the surface forcing; th e corresponding total ice production estimated from the temperature da ta would be 0.14 m, a bit more than the measured ice production 0.10 m . Predictions of the consolidated layer growth, based on (a) ice surfa ce temperature or (b) air temperature or (c) local undeformed ice grow th, gave good results. In spring the ice blocks throughout the keel be neath the consolidated layer melted uniformly.