Ice growth and solar heating in springtime leads

The large thermal contrast between the cold atmosphere and the relatively w arm ocean in springtime leads results in rapid ice growth and large fluxes of heat from the ocean to the atmosphere and of salt from the ice to the oc ean, However, the magnitude of the ice growth and of the fluxes is moderate d by solar radiation absorbed in the ice and upper ocean, During the Arctic lead experiment (LeadEx) we monitored ice conditions at four springtime le ads during the first few days of growth. The experiment took place in March -April 1992 in the Beaufort Sea (73 degrees N, 146 degrees W). Two of the l eads were <200 m in width, one was approximately a kilometer wide, and the fourth was quite large, more than a few kilometers wide. Ice thickness typi cally increased rapidly, with 15-20 cm of growth in the first few days. The crystallographic analysis of a series of ice cores taken across and along the edge of one of the smaller leads indicated that granular ice was more a bundant along the edges (30%) of the lead than in the central part of the l ead (10%). Observations suggest that thermodynamics processes dominated ice growth in these leads. Additional thickening of the ice at the edge of the leads was common because of rafting of the young ice and the accumulation of blowing snow. Ice temperature profiles exhibited a diurnal cycle induced by solar radiation, with daily oscillations of roughly 5 degrees C observe d in the interior of the lead ice. Theoretical simulations for one lead ind icated that during the first few days of ice growth, 30% of the incident so lar irradiance was absorbed in the ice and 25% was absorbed in the upper oc ean. The total amount of solar energy absorbed in the ice during this perio d was roughly equivalent to 4 cm of ice growth. The solar heating in ice an d water is roughly comparable in magnitude to the net longwave and is appro ximately two thirds of the turbulent fluxes.