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Abstract. The Antarctic Peninsula is one of the world's regions most affected by climate change. Several ice shelves have retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased

Abstract. Pine Island Glacier is the largest current Antarctic contributor to sea-level rise. Its ice loss has substantially increased over the last 25 years through thinning, acceleration and grounding line retreat. However, the calving line positions of the stabilising ice shelf did not show any trend within the observational record (last 70 years) until calving in 2015 led to unprecedented retreat and changed the alignment of the calving front. Bathymetric surveying revealed a ridge below the former ice shelf and two shallower highs to the north. Satellite imagery shows that ice contact on the ridge was likely lost in 2006 but was followed by intermittent contact resulting in back stress fluctuations on the ice shelf. Continuing ice-shelf flow also led to occasional ice-shelf contact with the northern bathymetric highs, which initiated rift formation that led to calving. The observations show that bathymetry is an important factor in initiating calving events.

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The Southern Annular Mode (SAM) is the predominant atmospheric variability mode in the Southern Hemisphere. In this paper, we present the spatial variability results of the SAM pattern for the period 1979-2018. The SAM-intrinsic pattern variability analysis is based on the principal component analysis (PCA), which is carried out for the ERA-Interim 500 hPa geopotential height (GPH) data set. A spatiotemporally resolved data set of SAM pattern maps (PCA loadings) is derived by projecting monthly shifted sub-sequences of SAM index values (PCA scores) on the corresponding GPH anomalies. The dominant SAM structure within single pattern fields is mapped automatically and can be interpreted as the Southern Hemisphere polar front. This data set allows an analysis of the geographical positions of the characteristic circumpolar SAM structure over four decades and shows considerable variability over space and time. Five different states of SAM patterns, which are associated with characteristic circulation anomalies during different phases of the study period, are identified. Station-based Antarctic temperature anomalies can be synoptically explained by these circulation anomalies. The overall latitudinal trend of the SAM pattern indicates an intensification of the meridional structure, especially over the East Antarctic Southern Ocean. Furthermore, we show that the SAM pattern variability is significantly correlated with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. Composites of 500 hPa GPH anomalies during the positive and negative phases of the respective indices indicate teleconnections with Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation, and this can explain latitudinal trends of the SAM pattern.