Sketch of a marine ice sheet. At the grounding line, the ice starts to float, forming an ice shelf.

Marine ice sheet dynamics

A marine ice sheet rests on a bed that is below sea level. At the grounding line, the ice becomes thin enough to float and the ice sheet forms an ice shelf. Ice shelves transmit changes in oceanic forcing (e.g., variations in basal melt rates through changing ocean temperatures) inland to the grounding line, influencing the grounding line’s position and stability. The loss of grounded ice contributes to sea level, and so determining the position and evolution of the grounding line is crucial for predictions of future sea level rise. Past and ongoing work focuses on understanding the dynamics of marine ice sheets, and identifying the main controls on the extent and stability of marine ice sheets (Haseloff & Sergienko, 2018; Haseloff & Sergienko, 2022).

Temperate ice

Top: simplified geometry of an ice stream/ridge system. Bottom: two examples of the temperature field in an ice stream with (green contour) and without (pink dotted contour) thermo-mechanical coupling and for two different hydraulic permeabilities of the temperate ice region (from Haseloff et al, 2019).

Temperate ice is ubiquitous in glaciers and ice sheets, forming where temperatures in the ice sheet reach the melting point. Further addition of heat to temperate ice (for instance through internal deformation or warming surface temperatures), leads to the formation of melt water embedded in the ice matrix. Even though the water content within the ice matrix is typically small (a few percent at most), the presence of water drastically alters the mechanical properties of ice. Moreover, water percolating through the ice to the base of the ice sheet can facilitate sliding of the ice along the bed, leading to increased ice discharge. Despite these important implications for ice sheet dynamics, the physical properties of temperate ice are poorly understood. Investigation of the interactions between temperate ice and ice sheet flow demonstrates that the properties of temperate ice can significantly alter the velocity field of ice streams (Haseloff et al., 2019) and ongoing work investigates the interaction of heat dissipation in ice stream margins with the subglacial water system and consequences for ice sheet dynamics (Law et al., in review).

Ice streams

Ice streams are fast-flowing regions of ice bordered by slowly moving ice. They are the main discharge routes for ice accumulated in the interior of an ice sheet. Observations suggest that the margins of some ice streams can migrate over time, leading to slow-down and reactivation cycles and drastically altering the ice sheet’s discharge. Past research on ice stream dynamics has focused on describing the thermal and mechanical processes that govern the migration of ice stream margins, which operate on length scales that are much smaller than typical grid sizes of continental-scale numerical ice sheet models (Haseloff et al., 2015, Haseloff et al., 2018).