On the importance of leads in sea ice to the energy balance and ice formation in the Weddell Sea

For a considerable coverage the energy balance of and ice formation by lead s in sea ice in the Weddell Sea are evaluated on the basis of data obtained from drifting buoys for the winter periods from 1986 to 1994 and by using a kinematic-thermodynamic sea ice model. The net heat flux is defined as th e sum total of radiative and turbulent fluxes. For thin ice the net turbule nt flux is 3-4 times the net radiative flux. The contribution of the net he at flux through open and refrozen leads to the total net heat flux through sea ice is twice as large as the area contribution of open and refrozen lea ds to the total area covered with sea ice. In the eastern and central parts of the Weddell Sea, leads contribute some 30% to the total energy flux fro m the ocean to the atmosphere. This flux increases from 10-15 W m(-2) in th e eastern and central Weddell Sea regions to 30 W m(-2) in the western part of the Weddell Sea, where leads contribute more than 80% of the total net energy transfer. The increase is mainly due to the colder and windier atmos phere in connection with the higher variability of the ice motion in the di urnal and semidiurnal band in the western Weddell Sea. The contribution of leads in winter ice formation exceeds 50% in the whole of the Weddell Sea. Monthly area-weighted ice growth is 10-15 cm in the east and up to 30 cm ov er the western continental shelf region. In the western part of the Weddell . Sea, tidal and inertial motions in the diurnal and semidiurnal bands enha nce lead formation, and thus contribute 7% to total net heat flux, 12% to i ce formation, and 23% to the salt mass released during ice growth. The resu lts are used to assess quantitatively the importance of leads to the intera ction of the ocean, the sea ice, and the atmosphere.