Modelling sea ice formation in the Terra Nova Bay polynya

• Main Authors: Sansiviero M, Morales Maqueda MA, Fusco G, Aulicino G, Flocco D, Budillon G
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier
• Subjects: Antarctic; Drygalski; Drygalski Ice Tongue; Ross Sea; Southern Ocean; Terra Nova Bay; Antarc*; Sea ice
• Online Access: https://eprint.ncl.ac.uk/fulltext.aspx?url=226938/AFD54701-AC0A-44D7-A297-DE53C78724D4.pdf&pub_id=226938

Antarctic sea ice is constantly exported from the shore by strong near surface winds that open leads and large polynyas in the pack ice. The latter, known as wind-driven polynyas, are responsible for significant water mass modification due to the high salt flux into the ocean associated with enhanced ice growth. In this article, we focus on the wind-driven Terra Nova Bay (TNB) polynya, in the western Ross Sea. Brine rejected during sea ice formation processes that occur in TNB polynya densifies the water column leading to the formation of the most characteristic water mass of the Ross Sea, the High Salinity Shelf Water (HSSW). This water mass, in turn, takes part in the formation of Antarctic Bottom Water (AABW), the densest water mass of the Southern Ocean, which plays a major role in the global meridional overturning circulation, thus affecting the global climate system. A simple coupled sea ice – ocean model has been developed to simulate the seasonal cycle of sea ice formation in, and export off, the polynya. The sea ice model accounts for both thermal and mechanical ice processes. The oceanic circulation is described by a one-and-a-half layer, reduced gravity model. The domain resolution is 1 km × 1 km, which is sufficient to represent the salient features of the coastline geometry, notably the Drygalski Ice Tongue. The model is forced by a combination of Era Interim reanalysis and in-situ data from automatic weather stations, and also by a climatological oceanic dataset developed from in situ hydrographic observations. The sensitivity of the polynya to the atmospheric forcing is well reproduced by the model when merging atmospheric in situ and reanalysis data, which allows us to capture in detail the strength and the spatial distribution of the katabatic winds that often drive the opening of the polynya. The model resolves fairly accurately the sea ice drift and sea ice production rates in the TNB polynya, leading to realistic polynya extent estimates. The model-derived polynya extent has been validated by comparing the modelled sea ice concentration against MODIS high resolution satellite images, confirming that the model is able to reproduce reasonably well the TNB polynya evolution in terms of both shape and extent.