Insights into Past Ice Sheets from Solid Earth Feedbacks

Disentangling the drivers of past ice sheet vulnerability is key to projecting future ice retreat and sea-level change. In particular, increased attention has focused on the importance of solid Earth-ice sheet interactions in modulating the vulnerability of marine ice sheets. In this talk, I consider how solid Earth feedbacks modulate ice sheet stability on millennial to glacial-interglacial timescales. First, I address the rapid demise of the Cordilleran Ice Sheet, which spanned the Rocky Mountains to the Pacific Ocean at the Last Glacial Maximum. Capturing the observed millennial timescale of ice retreat requires a full treatment of transient rheology and regionally-appropriate Earth structure. By deepening topographic highs that underpinned the ice sheet, solid-Earth feedbacks rendered the Cordilleran Ice Sheet susceptible to catastrophic retreat. This mechanism underscores the potential for solid-Earth feedbacks to pace millennial-scale global climate events by controlling the timing of ice retreat and associated freshwater fluxes.

Next, I consider the role of ice sheet-solid Earth interactions on the deglaciation of the Ross Sea in West Antarctica. Since the Last Glacial Maximum, ice streams in the Ross Sea retreated hundreds of kilometers from the shelf break to their modern grounding line positions. I show that glacial isostatic adjustment causes a net retreat of stable grounding line positions from 20 ka to modern, with some ice streams experiencing up to 1000 km of stable grounding line zone retreat. This finding differs from prior studies that cite glacial isostatic adjustment as a stabilizing mechanism for marine-terminating ice streams, and underlines that solid Earth-ice sheet feedbacks are a function of both timescale and spatial scale of ice sheet unloading.

Speaker: Tamara Pico, UC Santa Cruz