Mechanisms for the link between onset and duration of open water in the Kara Sea

The sea ice conditions in the Kara Sea have important impacts on Arctic shipping, oil and gas production, and marine environmental changes. In this study, sea ice coverage ( C R ) less than 30% is considered as open water, its onset and end dates are defined as T open and T close , respectively. The sea ice melt onset ( T melt ) is defined as the date when ice-sea freshwater flux initially changes from ice into the ocean. Satellite-based sea ice concentration (SIC) from 1989 to 2019 shows a negative correlation between T open and T close ( r = −0.77, p < 0.01) in the Kara Sea. This phenomenon is also obtained through analyzing the hindcast simulation from 1994 to 2015 by a coupled ocean and sea-ice model (NAPA1/4). The model results reveal that thermodynamics dominate the sea ice variations, and ice basal melt is greater than the ice surface melt. Heat budget estimation suggests that the heat flux is significant correlated with T open ( r = −0.95, p < 0.01) during the melt period (the duration of multi-year averaged T melt to T open ) influenced by the sea ice conditions. Additionally, this heat flux is also suggested to dominate the interannual variation of the heat input during the whole heat absorption process ( r = 0.81, p < 0.01). The more heat input during this process leads to later T close ( r = 0.77, p < 0.01). This is the physical basis of the negative correlation between T open and T close . Therefore, the duration of open water can be predicted by T open and thence support earlier planning of marine activities.