Deuterium concentration in congelation sea ice is dependent on the freezing rate. The growth rate can be determined using a box diffusion model where the initial sea water ΔD value is kept constant in the course of freezing outside a boundary layer developed close to the ice interface. For the boundary layer thickness estimated from Na concentration measurements, the model gives results in accordance with previous studies of sea ice growth rates. ¿ American Geophysical Union 1988