A Volume‐Conserved Approach to Estimating Sea‐Ice Production in Antarctic Polynyas

Accurate estimation of sea‐ice production (SIP) is crucial to understanding the formation of Antarctic Bottom Water (AABW). Existing SIP estimates depend on the heat‐budget method, using atmospheric reanalysis together with satellite‐derived sea‐ice thickness data, and make an unrealistic assumption of no ocean heat flux occurring below the ice. Here, we propose a new method to estimate SIP based on the sea‐ice volume‐conservation (VC) theory. This new method can consider cases with sea‐ice melting (negative SIP). For a latent‐heat polynya—the Ross Sea Polynya—this method captures the synoptic SIP variations affected by warm‐water intrusions, including small‐scale melting and freezing patterns. Using the new VC approach for a sensible‐heat polynya, the Maud Rise Polynya, the sub‐sea‐ice oceanic heat flux was indirectly estimated, and the sea‐ice melting rate induced by warm water uplifted by Ekman pumping was estimated to be 0.15 and 1.44 cm d−1 for 2016 and 2017, respectively. Plain Language Summary Polynyas are regions of open water or thin sea‐ice surrounded by more extensive or thicker sea‐ice. Polynyas can be classified into sensible‐heat polynyas caused by sea‐ice melting and latent‐heat polynyas caused by sea‐ice divergence. Active atmosphere–ocean heat exchange and sea‐ice production (SIP) lead to strong heat loss (in latent‐heat polynyas) and intense sea‐ice formation (in sensible‐heat polynyas), which forms dense shelf water—a precursor to Antarctic Bottom Water. By assuming a zero sub‐ice oceanic heat flux, previous estimations of ice production based on the heat‐budget method are mainly limited to latent‐heat polynyas. In this study, based on the sea‐ice volume‐conservation theory, we developed a new method to estimate SIP and the melting rate. Moreover, using this method, we estimated the ice–ocean heat flux via satellite observations. For a latent‐heat polynya (the Ross Sea Polynya), we captured the synoptic melting that resulted from warm‐water intrusion well. For a sensible‐heat polynya (the Maud Rise Polynya), we found that the uplift of warm water by Ekman pumping was crucial to maintenance of the polynya. Key Points A new volume‐conservation‐based method using only satellite observations is proposed to estimate sea‐ice production in Antarctic polynyas The new method can determine the sub‐sea‐ice oceanic heat flux at the Maud Rise Polynya, which correlates well with Ekman upwelling The results show that the warm modified Circumpolar Deep