Towards a new Antarctica-wide basal melt rate product

Abstract:

Subglacial meltwater is formed at the base of the Antarctic ice sheet due to geothermal heat flux and frictional dissipation. This basal meltwater plays a key role in ice-sheet dynamics, such as lubricating the base of ice streams and is the source of water for many subglacial lakes. The outflow of subglacial meltwater at the grounding line can also act to trigger sub-ice shelf melting.

Here we present results concerning basal melt rates and subglacial hydrology from the ESA project 4DAntarctica. An objective of this work is to determine the basal dissipation component of basal melt rate. We use STREAMICE, the ice-flow modelling component of MITgcm, along with OpenAD to calculate the adjoint model, inverting for basal-friction and ice-stiffness parameters. The results of the model inversion are used to determine basal dissipation from the product of the basal shear stress and basal speed.

We present results from two case studies that we have used to refine our methodology. Firstly the Amery subglacial catchment, where we assess the impact of changing the spatial resolution of the ice model. We find that total calculated melt rate is reduced by 5% when a coarser model is used, with up to an 80% reduction found at the onset of fast flow in ice streams. These differences in melt rate lead to spatial variation in the subglacial hydrology.

Secondly, we consider the Amundsen subglacial catchment and include additional constraints on surface elevation change in the inversion. This allows the constraint on the uncertain ice-stiffness parameter to be reduced and produces a more representative flow field and therefore more accurate basal melt rate. Finally we present preliminary results from our Antarctic-wide melt rate product.