Subglacial fresh-water discharge from the AIS into the Southern Ocean (D3.3)

This deliverable relates to the modelling and quantification of basal melt rates produced within the interior of the Antarctic Ice Sheet due to basal sliding. As ice slides over the glacier bed, frictional heat is produced causing melting of basal ice. Calculating the resulting rate of melt-watermeltwater productions involves estimating two quantities: Thethe speed by which the ice slides over the bed, and the stresses acting on the bed through the flow of ice. We used state-of-the-art data assimilation methods to estimate those quantities, whereby measurements of surface velocities served, as reported by ITS_LIVE, serve to tightly constrain physical model parameters related to ice flow. This gave us a new estimate of basal water production for the whole of the Antarctic Ice Sheet. In areas of high flow, we find that basal water production is on the order of a few meters per year. In comparison, basal water production due to geothermal heat flux is typically on the order of a few millimetres, or in other words: three orders of magnitude smaller. Furthermore, due to the absence of reliable estimates of the geothermal heat flux, estimates of related basal -water production are at best educated guessguesses. In contrast, our estimates of basal water production due to sliding are highly constrained by measurements. Additionally, we have developed a new water-routing algorithm and applied this the key areas of the Antarctic Ice Sheet. The new subglacial water-routing algorithm does not suffer from mesh-resolution dependency issues, as some previously published approaches to this problem (Le Brocq et al. 2009) and does not require a separate “filling algorithm” to fill local depressions in the water potential.