Modelling the subglacial hydrology of the former Barents Sea Ice Sheet

Ice dynamics are strongly controlled by processes taking place at the interface between the ice and the underlying bed. In modern day ice sheets, up to 90% of mass is lost through fast-flowing corridors of ice, called ice streams. These are typically underlain by a thin layer of water and wet sediment, both of which promote fast flow. In recent years it has emerged that subglacial hydrology played an important role in the relatively fast disintegration of the Fennoscandian and the Barents Sea Ice Sheets (BSIS). The BSIS is a close historical analogue to the West Antarctic Ice sheet (WAIS) and understanding its demise could give important insight into the future evolution of the WAIS. In this study, we investigate the effect of subglacial water on the evolution of the Fennoscandian and the Barents Sea Ice Sheets. We do this by implementing a thin film model of water flow into an existing numerical ice sheet model and simulate the ice sheets growth and decay during the last glacial cycle. Additionally, we examine the influence of a subglacial lake on ice dynamics and isochrone layers within the ice. Basal water separates the ice and bed, softens the underlying sediments and greatly increases ice velocity. Including subglacial hydrology in numerical ice sheet models leads to less ice building up with time during glacial periods. Temperate areas of ice sheets are typically overestimated without it and deglaciation occurs more slowly. Subglacial water can form lakes underneath the ice that greatly affect its speed and thermal regime. Lake drainage can result in travelling waves at depth within isochrone layers, indicating the possibility of detecting past drainage events with ice penetrating radar. The effects of subglacial hydrology are important and accounting for them will be necessary in order to accurately estimate polar contributions to sea level change in the future

Modelling the subglacial hydrology of the former Barents Sea Ice Sheet

Ice dynamics are strongly controlled by processes taking place at the interface between the ice and the underlying bed. In modern day ice sheets, up to 90% of mass is lost through fast-flowing corridors of ice, called ice streams. These are typically underlain by a thin layer of water and wet sediment, both of which promote fast flow. In recent years it has emerged that subglacial hydrology played an important role in the relatively fast disintegration of the Fennoscandian and the Barents Sea Ice Sheets (BSIS). The BSIS is a close historical analogue to the West Antarctic Ice sheet (WAIS) and understanding its demise could give important insight into the future evolution of the WAIS. In this study, we investigate the effect of subglacial water on the evolution of the Fennoscandian and the Barents Sea Ice Sheets. We do this by implementing a thin film model of water flow into an existing numerical ice sheet model and simulate the ice sheets growth and decay during the last glacial cycle. Additionally, we examine the influence of a subglacial lake on ice dynamics and isochrone layers within the ice. Basal water separates the ice and bed, softens the underlying sediments and greatly increases ice velocity. Including subglacial hydrology in numerical ice sheet models leads to less ice building up with time during glacial periods. Temperate areas of ice sheets are typically overestimated without it and deglaciation occurs more slowly. Subglacial water can form lakes underneath the ice that greatly affect its speed and thermal regime. Lake drainage can result in travelling waves at depth within isochrone layers, indicating the possibility of detecting past drainage events with ice penetrating radar. The effects of subglacial hydrology are important and accounting for them will be necessary in order to accurately estimate polar contributions to sea level change in the future

Subglacial roughness of the former Barents Sea ice sheet

The roughness of a glacier bed has high importance for the estimation of the sliding velocity and can also provide valuable insights into the dynamics and history of ice sheets, depending on scale. Measurement of basal properties in present-day ice sheets is restricted to ground-penetrating radar and seismics, with surveys retrieving relatively coarse data sets. Deglaciated areas, like the Barents Sea, can be surveyed by shipborne 2-D and 3-D seismics and multibeam sonar and provide the possibility of studying the basal roughness of former ice sheets and ice streams with high resolution. Here, for the first time, we quantify the subglacial roughness of the former Barents Sea ice sheet by estimating the spectral roughness of the basal topography. We also make deductions about the past flow directions by investigating how the roughness varies along a 2-D line as the orientation of the line changes. Lastly, we investigate how the estimated basal roughness is affected by the resolution of the basal topography data set by comparing the spectral roughness along a cross section using various sampling intervals. We find that the roughness typically varies on a similar scale as for other previously marine-inundated areas in West Antarctica, with subglacial troughs having very low roughness, consistent with fast ice flow and high rates of basal erosion. The resolution of the data set seems to be of minor importance when comparing roughness indices calculated with a fixed profile length. A strong dependence on track orientation is shown for all wavelengths, with profiles having higher roughness across former flow directions than along them

The effect of sedimentation in a subglacial lake on the dynamics of an artificial ice stream

As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocity and a subsequent lowering of the ice surface in the vicinity of the upstream lake edge. Conversely, at the downstream end of the lake a small hump is observed as the ice velocity decreases near the point of contact with land. There are two contributions arising from the ice/lake interaction: (1) changes in the thermal regime that propagate downwards with the advection of ice and (2) the increase in flow speeds caused by basal sliding over the lake surface. Sediment transport from upstream areas into subglacial lakes changes their size, thus reducing the area of the ice/lake interface. Here, we aim to study the effect that this reduction in size has on the flow dynamics and the surface elevation of an artificial ice stream and the temporal evolution of this effect. To this end, we use a full-Stokes, polythermal ice flow model, implemented into the commercial finite element software COMSOL Multiphysics. An enthalpy gradient method is used in order to account for the evolution of temperature and water content within the ice. This conceptual model uses prescribed boundary velocity and temperature profiles and a Weertman-type sliding law with a fixed parameter combination. In order to separate the effect of the slow thermal contribution from the fast mechanical one, we will present sensitivity tests that additionally involve a thermally-constant flow

Eurasian ice-sheet dynamics and sensitivity to subglacial hydrology

Ice-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity