The response of the Ross Ice Shelf to mechanical contact with pinning points

Small-scale ice shelf pinning points modify the mechanics and dynamics of marine ice sheets, yet pinning point attributes are poorly represented in ice flow models used to interpret present-day change and predict future ice sheet behaviour. Here, we use the Ice Sheet System Model (ISSM) to examine how a collection of smaller-scale pinning points in the eastern Ross Ice Shelf (RIS) modify the mechanics and dynamics of the interconnected ice sheet-ice shelf system. Simulations of RIS and tributary ice stream flow, with and without the Shirase Coast Ice Rumples (SCIR) included in the model domain, are used to quantify the pinning point contribution to flow-resisting stresses.

We examine, in detail, the partitioning of resistive stresses with and without the SCIR, and the associated velocity and thickness fields across the eastern RIS. While pinning points are widely recognised to generate upstream compression, other regional modifications to resistive stresses are also important. For example, when the SCIR are removed from the model, longitudinal stretching and ice velocity increase, however, lateral drag generated by other grounded features also increases, providing a control on the speed change. In this way, the coupled ice sheet-ice shelf system moderates its response to changes in pinning point configuration.

We also examine how the representation of pinning points via a basal friction coefficient conditions the behaviour of the ice stream-ice shelf system. Naive inversion of present-day flow and thickness to infer basal friction leads to an incorrect representation of ice rumple morphology. We improve upon the inferred basal friction values by completing a detailed force budget, and via model tuning to generate a realistic SCIR morphology. Other basal friction effects are less direct. MacAyeal Ice Stream, located directly upstream of the SCIR, is less responsive to the loss of the ice rumples than the obliquely oriented Bindschadler Ice Stream, due to larger basal drag acting on the main trunk of MacAyeal Ice Stream. Where pinning point effects are important, careful tuning that respects ice rumple morphology should be employed.