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Antarctica and Greenland hold enough ice to raise sea level by more than 65m if both ice sheets were to melt completely. Predicting future ice sheet mass balance depends on our ability to model these ice sheets, which is limited by our current understanding of several key physical processes, such as iceberg calving. Large-scale ice flow models either ignore this process or represent it crudely. To model fractured zones, an important component of many calving models, continuum damage mechanics as well as linear fracture mechanics are commonly used. However, these methods have a large number of uncertainties when applied across the entire Antarctic continent because the models were typically tuned to match processes seen on particular ice shelves. Here we present an alternative, statistics-based method to model the most probable zones of the location of fractures and demonstrate our approach on all main ice shelf regions in Antarctica, including the Antarctic Peninsula. We can predict the location of observed fractures with an average success rate of 84% for grounded ice and 61% for floating ice and a mean overestimation error rate of 26% and 20 %, respectively. We found that Antarctic ice shelves can be classified into groups based on the factors that control fracture location. [ABSTRACT FROM AUTHOR]

Abstract: The silicon (Si) isotope (δ 30Si) composition of deep-sea sponges from near Antarctica, subantarctic waters (Tasmania Seamounts) and subtropical waters north of New Zealand vary widely between +0.87‰ and −3.40‰ (vs. NBS28). Depth profiles show that sponge δ 30Si compositions trend to lower values with increasing depth. This is exemplified by sponges from the Tasmania Seamounts where δ 30Si varies from +0.87‰ to −3.13‰ over a depth range from 100m to 1200m. These changes in δ 30Si of sponges are inconsistent with a Rayleigh type isotope fractionation model requiring constant δ 30Si fractionation between sponge and seawater. We conclude that overall Si isotope fractionation Δ 30Si (δ 30Si sponge – δ 30Si seawater) is influenced by seawater Si concentration, with more fractionated (lower) isotope values being associated with sponges collected from waters high in Si. We invoke and fit a model whereby the Δ 30Si fractionation varies as a function Si influx and efflux. Using this model it appears that Δ 30Si fractionation during transport into the sponge is constant at −1.34‰. The model also shows asymptotic behaviour with Δ 30Si trending towards a maximum of −6.02‰ at very high Si concentrations. These results suggest that the δ 30Si composition of fossil spicules may be useful for reconstruction paleo-Si concentrations during the past. [Copyright &y& Elsevier]