The empirical basis for modelling glacial erosion rates

Glaciers are highly effective agents of erosion that have profoundly shaped Earth’s surface, but there is uncertainty about how glacial erosion should be parameterised in landscape evolution models. Glacial erosion rate is usually modelled as a function of glacier sliding velocity, but the empirical basis for this relationship is weak. In turn, climate is assumed to control sliding velocity and hence erosion, but this too lacks empirical scrutiny. Here, we present statistically robust relationships between erosion rates, sliding velocities, and climate from a global compilation of 38 glaciers. We show that sliding is positively and significantly correlated with erosion, and derive a relationship for use in erosion models. Our dataset further demonstrates that the most rapid erosion is achieved at temperate glaciers with high mean annual precipitation, which serve to promote rapid sliding. Precipitation has received little attention in glacial erosion studies, but our data illustrate its importance

RECONSTRUCTING THE GLACIAL HISTORY OF WESTERN DRONNING MAUD LAND, ANTARCTICA, USING HIGH-RESOLUTION NUMERICAL ICE SHEET MODELLING AND GEOMORPHOLOGICAL MAPPING

Given current concern about the stability of ice sheets, and potential sea level rise, it is imperative that we are able to reconstruct and predict the response of ice sheets to climate change. The Intergovernmental Panel on Climate Change (IPCC), amongst others, have highlighted that our current ability to do so is limited. Numerical ice sheet models are a central component of the work to address this challenge. An unresolved key issue in this work concerns the volume and rate of ice mass loss needed to explain the large difference between late glacial and interglacial global sea levels. Some 20% of observed sea level rise since the Last Glacial Maximum (LGM) cannot be attributed to any known former ice mass, indicating that this inconsistency arises from the deficiencies in modelled reconstructions of ice sheet volumes and postglacial rebound. Ice sheet models are tested and refined by comparing model predictions of past ice geometries with field-based reconstructions from geological, geomorphological and ice core data. However, on the East Antarctic Ice sheet, Dronning Maud Land (DML) presents a critical gap in the empirical data required to reconstruct changes in ice sheet geometry. In addition, there is poor control on regional climate histories of ice sheet margins, because ice core locations, where detailed reconstructions of climate history exist, are located on high inland domes. This leaves numerical models of regional glaciation history largely unconstrained. MAGIC-DML is a Swedish-US-Norwegian-German-UK collaboration with a focus on filling the critical data gaps that exist in our knowledge of the timing and pattern of ice surface changes on the western Dronning Maud Land margin. Here we describe a series of high-resolution modelling experiments to help identify those areas across western Dronning Maud Land that are the most sensitive to uncertainties in the regional climate history and the choice of model parameters. For this we employ a wide range of climate and ocean histories combining published outputs of 18 general circulation models for the LGM and mid-Holocene with ice core records. The modelling results together with remote sensing mapping of glacial landforms is informing and guiding cosmogenic nuclide sampling campaigns in western Dronning Maud Land starting 2016/17. Successful integration of numerical modelling and field investigations in an iterative manner is key to achieving the anticipated outcome of the MAGIC-DML project, a reconstruction of the long-term pattern and timing of vertical changes in ice surface elevation since the mid-Pliocene warm period, which will provide the missing empirical data required to constrain numerical ice sheet models

Inland thinning of West Antarctic Ice Sheet steered along subglacial rifts

Current ice loss from the West Antarctic Ice Sheet (WAIS) accounts for about ten per cent of observed global sea-level rise1. Losses are dominated by dynamic thinning, in which forcings by oceanic or atmospheric perturbations to the ice margin lead to an accelerated thinning of ice along the coastline2, 3, 4, 5. Although central to improving projections of future ice-sheet contributions to global sea-level rise, the incorporation of dynamic thinning into models has been restricted by lack of knowledge of basal topography and subglacial geology so that the rate and ultimate extent of potential WAIS retreat remains difficult to quantify. Here we report the discovery of a subglacial basin under Ferrigno Ice Stream up to 1.5 kilometres deep that connects the ice-sheet interior to the Bellingshausen Sea margin, and whose existence profoundly affects ice loss. We use a suite of ice-penetrating radar, magnetic and gravity measurements to propose a rift origin for the basin in association with the wider development of the West Antarctic rift system. The Ferrigno rift, overdeepened by glacial erosion, is a conduit which fed a major palaeo-ice stream on the adjacent continental shelf during glacial maxima6. The palaeo-ice stream, in turn, eroded the ‘Belgica’ trough, which today routes warm open-ocean water back to the ice front7 to reinforce dynamic thinning. We show that dynamic thinning from both the Bellingshausen and Amundsen Sea region is being steered back to the ice-sheet interior along rift basins. We conclude that rift basins that cut across the WAIS margin can rapidly transmit coastally perturbed change inland, thereby promoting ice-sheet instability

Evidence of topographic disequilibrium in the Subarnarekha River Basin, India: A digital elevation model based analysis

Cratonic areas experience complex process-response changes due to their operative endogenic and exogenic forces varying in intensity and spatiality over long timescales. Unlike zones of active deformation, the surface expression of the transient signals in relatively tectonically stable areas are usually scant. The Subarnarekha River Basin, in eastern India, is a prime example of a Precambrian cratonic landscape, overlain in places by Tertiary and Quaternary deposits. A coupled quantitative-qualitative approach is employed towards deciphering tectonic and geological influences across linear and areal aspects, at the basin and sub-basin scale. Within this landscape, the transient erosional signatures are explored, as recorded in the disequilibrium conditions of the longitudinal profiles of the major streams, which are marked by a number of waterfalls at structural and lithological boundaries. Mathematical expressions derived from the normalized longitudinal profiles of these streams are used to ascertain their stage of development. Cluster analysis and chi plots provide significant interpretations of the role of vertical displacements or litho-structural variations within the basin. These analyses suggest that a heterogeneous, piece-meal response to the ongoing deformation exists in the area, albeit, determining the actual rate of this deformation or its temporal variation is difficult without correlated chronological datasets.by Shantamoy Guha and Priyank Pravin Pate