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Monitoring the Antarctic sea‐ice is essential for improving our knowledge of the Southern Ocean. We used satellite sea‐ice concentration data for the 2002–2020 period to retrieve the sea‐ice extent (SIE) and analyze its variability in the Pacific sector of the Southern Ocean. Results provide observational evidence of the recurring formation of a sea‐ice protrusion that extends to 60°S at 150°W during the winter season. Furthermore, we discuss how the Pacific‐Antarctic Ridge (PAR) influences this phenomenon. Our findings show that the northward deflection of the southern Antarctic Circumpolar Current front is driven by the PAR and is associated with the enhanced sea‐ice advance. The PAR also constrains eddy trajectories, limiting their interaction with the sea‐ice edge. These factors, within the 160°W–135°W sector, cause an average SIE increase of 61,000 km2 and 46,293 km2 per year more than the upstream and downstream areas, respectively. Plain Language Summary: Monitoring the variability of marine and continental ice is essential for the study of climate change. The aim of this study is to investigate the processes that favor the formation or melting of sea‐ice in the Pacific sector of the Southern Ocean. To this end, we analyzed sea‐ice variability over the last two decades (2002–2020) and its interaction with the Antarctic Circumpolar Current (ACC) and the Pacific‐Antarctic Ridge (PAR), a topographic submarine feature that separates the Pacific and Antarctic plates. We used satellite data obtained through passive microwave sensors and altimetry for sea‐ice and ACC eddy analysis, respectively. Our results provide observational evidence of the periodic formation of a sea‐ice protrusion in the study area and show that the median extent of the sea‐ice faithfully follows the PAR. Moreover, our results show that the PAR acts as a barrier that deflects the ACC and its associated eddies northward, which limits their ability to melt the sea‐ice east of the PAR. These processes encourage the exceptional growth of the sea‐ice in this area. These outcomes have strong implications for our understanding of sea‐ice variability over the Southern Ocean. Key Points: The Pacific‐Antarctic Ridge diverts warm and cold core eddies northward, encouraging an expansion of Antarctic sea‐ice at 150°WThe Southern Ocean is characterized by the recurring formation of a sea‐ice protrusion that extends to 60°S between 150°W and 140°W [ABSTRACT FROM AUTHOR]

A composite dataset (comprising geopotential height, sea surface temperature, zonal and meridional surface winds, precipitation, cloud cover, surface air temperature, latent plus sensible heat fluxes, and sea ice concentration) has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013. Three covarying climate signals associated with variations in the sea ice distribution around Antarctica have been detected through the application of the multiple-taper method with singular value decomposition (MTM-SVD). Features of the established patterns of variation over the Southern Hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations. The climate patterns considered here are the southern annular mode (SAM), the Pacific-South American (PSA) teleconnection, the semiannual oscillation (SAO), and the zonal wavenumber-3 (ZW3) mode. It is shown that most of the sea ice temporal variance is concentrated at the quasi-triennial scale resulting from the constructive superposition of the PSA and ZW3 patterns. In addition, the combination of the SAM and SAO patterns is found to promote the interannual sea ice variations underlying a general change in the Southern Ocean atmospheric and oceanic circulations. These two modes of variability are also found to be consistent with the occurrence of the positive SAM/negative PSA (SAM¹/PSA²) or negative SAM/positive PSA (SAM²/PSA¹) combinations, which could have favored the cooling of the sub-Antarctic region and important changes in the Antarctic sea ice distribution since 2000. [ABSTRACT FROM AUTHOR]

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 the 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 world 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 and export within a 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 atmospheric in situ measurements are combined with reanalysis data. Merging the two datasets 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. [ABSTRACT FROM AUTHOR]