The energy budget and the formation of sea ice in the eastern Weddell Sea west of Maud Rise are investigated on a regional scale on the basis of data obtained from drifting buoys deployed during the ANZFLUX project in 1994. A one-dimensional model for snow-covered sea ice and a kinematic-thermodynamic sea ice model for ice formed in leads are coupled and run under atmospheric and oceanic conditions specified from in situ data. Flooding at the snow-ice interface and snow ice formation need to be accounted for to achieve reasonable agreement between modeled and measured temperature distributions. The time-averaged values for the net heat flux are 21 W m-2, some 60% of which originate in refreezing leads, and 9.8 cm for the monthly rate of ice accumulation. Whereas leads contribute a net accumulation of 10.8 cm, the mass balance of consolidated, snow-covered ice results in a net ablation of -1.0 cm. Sensitivity studies reveal the contribution of processes related to snow cover and ocean heat flux to sea ice formation and heat exchange. Without taking snow ice formation into account, a net ablation of -14.9 cm occurs under snow-covered ice due to high oceanic heat fluxes. A comparison between a simple two-layer model and the one-dimensional thermodynamic model emphasizes the influence of heat storage in sea ice on the development of heat flux and ice thickness. The heat and mass fluxes obtained on a regional scale, and their sensitivity to the parameterizations, elucidate the implication of vigorous small-scale processes on sea ice development and point out their importance for sea ice models.