Description: Much of Arctic sea ice forms over the shallow continental shelves along the perimeter of the basin. Ice which escapes the shelf is transported several years within the Beaufort Gyre and Transpolar Drift stream, before exiting the Arctic Basin through Fram Strait. This ice, and especially that in the Siberian branch of the Transpolar Drift stream in the Eurasian Basin, may incorporate large quantities of particulate matter during formation on the shelf. Subsequent seasonal surface melting and winter freezing on the ice underside results in surface accumulation of particulate matter. Rafting of floes over and under each other results in a complex ice stratigraphy and redistribution of sediment accumulations. In contrast, Antarctic sea ice has only limited sources for sediment incorporation, and most of the ice-cover melts each year. These variations in Arctic and Antarctic ice characteristics are illustrated by analyses of ice crystal texture, c-axis orientations, salinity, δ 18O on ice cores and discussion of potential sediment input.

Description: The stability of ice shelves depends on the existence of embayments and is largely influenced by ice rises and ice rumples, which act as “pinning-points” for ice shelf movement. Of additional critical importance are interactions between ice shelves and the water masses underlying them in ice shelf cavities, particularly melting and refreezing processes. The present study aims to elucidate the role of ice rises and ice rumples in the context of climate change impacts on Antarctic ice shelves. However, due to their smaller spatial extent, ice rumples react more sensitively to climate change than ice rises. Different forcings are at work and need to be considered separately as well as synergistically. In order to address these issues, we have decided to deal with the following three issues explicitly: oceanographic-, cryospheric and general topics. In so doing, we paid particular attention to possible interrelationships and feedbacks in a coupled ice-shelf-ocean system. With regard to oceanographic issues, we have applied the ocean circulation model ROMBAX to ocean water masses adjacent to and underneath a number of idealized ice shelf configurations: wide and narrow as well as laterally restrained and unrestrained ice shelves. Simulations were performed with and without small ice rises located close to the calving front. For larger configurations, the impact of the ice rises on melt rates at the ice shelf base is negligible, while for smaller configurations net melting rates at the ice-shelf base differ by a factor of up to eight depending on whether ice rises are considered or not. We employed the thermo-coupled ice flow model TIM-FD3 to simulate the effects of several ice rises and one ice rumple on the dynamics of ice shelf flow. We considered the complete un-grounding of the ice shelf in order to investigate the effect of pinning points of different characteristics (interior or near calving front, small and medium sized) on the resulting flow and stress fields, focusing on the floating ice parts of the Brunt and Riiser-Larsen ice shelves. The major response of the ice is observed instantaneously and is caused by the time independent nature of the Stokes equations and the used Glen-type rheology. The influence of ice temperatures and therefore the time-dependent effect on the flow-rate are small, given a 100 year time frame and applying a fixed-geometry setting.. A particularly important result of the current project lies in the fact that we have numerically simulated the three-dimensional stress fields in an ice shelf. Common numerical models that utilize a vertically integrated Shallow Shelf Approximation (SSA-models), do not provide that information. Due to the detailed horizontal resolution of 1km in our models, we were able to also model the observed heavily fractured areas in the vicinity of McDonald Ice Rise, a region that is characterized by simulated tensile stresses reaching maximum vertical extension in the ice column.