What causes changes in ice sheet flow?
In the Greenland and Antarctic ice sheets, ice primarily moves by flow in individual glaciers or "ice streams". We want to understand how and why the flow in these glaciers changes over time. We do so by tracking the time scales and magnitudes of changing mass flow in glaciers occurring due to different mechanisms. These changes can be caused by climate (Robel & Tziperman 2016, Robel et al. 2018), internally-generated variations in ice melt and friction beneath glaciers (so-called thermal oscillations, Robel et al. 2013, 2014), ice fabric and temperature (Minchew et al. 2018), or ocean tides (Robel et al. 2017). By explaining the causes and rates of glacier changes, we can improve our understanding past ice sheet deglaciations, distinguish natural from human-caused changes in the present, and more accurately predict future ice sheet melt.
What controls iceberg calving?
Ice sheets that end in water lose ice through the process of iceberg calving (ice fracture and detachment). Calving is likely influenced by many factors within and outside of ice sheets, including the presence of sea ice within densely packed icebergs floating in the ocean, known as "mélange". We have adapted a discrete element model, a tool more commonly used in condensed matter physics, to explore the role of sea ice and calving in the aggregate properties of iceberg mélange (Robel 2017). We continue to develop tools to help us understand the effect of thinning sea ice on mélange and the dispersion of icebergs in the ocean.
How and why do ice sheets collapse?
There is evidence that ice sheets and glaciers can become unstable under the right conditions, leading to their irreversible and rapid decline. We are examining which climatic and geological conditions may lead to these instabilities and how fast ice sheets melt when they become unstable. One recent avenue of research has shown the potential role of ice sheet geometry in causing the most rapid periods of sea level rise in recent Earth history (Robel & Tsai 2018). We have also explored the role of changing friction at the bottom of ice sheets (Robel et al. 2016) and the multiple time scales and mechanisms of marine ice sheet collapse (Robel et al. 2018). We are currently exploring the role of ice sheet instabilities in generating fat-tailed uncertainty in projections of future sea level rise (stay tuned!).