bradley paul lipovsky
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My first focus is glacier sliding. Previously, I have used observations of tidally-modulated stick-slip cycles on the Whillans Ice Stream, Antarctica, to quantify the evolution of ice stream basal strength (Lipovsky and Dunham, 2017, JGR). Remarkably, these slip events occur twice per day and result in ~m of slip over a 40,000 sq km area. The cumulative effect of these stick-slip cycles is a net, decadal deceleration of ice flow which, if it continues, will change the sign of the mass balance for the entire Antarctic ice sheet (c.f., Beem et al., 2014, JGR; Rignot et al., 2008, Nature). I have taken an interdisciplinary approach towards modeling these events by using rate-and-state friction, a time-dependent sliding law originally formulated to describe the tectonic earthquake cycle. The primary technical innovation in this work was the use of a linearized stability analysis to describe the conditions required for the existence of ice stream stick slip cycles.

Because of the huge potential for the WIP to shake things up in the Antarctic Ice Sheet, I made a lighthearted wager with Paul Winberry and Sridhar Anandakrishnan. The bet is that the WIP is going to continue to stagnate in the next decade. Paul and Sridar think that I'm wrong about this, which makes the wager interesting. The details are that the flow of ice sourced from the Whillans Ice Stream will have less than 100 m/a maximum flow velocity over the grounding line, wherever that may be, on the 25th day of June, 2027. I'm pretty sure that I'm right about this one.

My second focus concerns iceberg calving. The physics of iceberg calving are currently responsible for discrepancies in the latest generation of predictive ice sheet models equivalent to 10~m of sea level rise by the year 2100 (c.f. DeConto and Pollard, 2016, Nature; Golledge et al., 2015, Nature). My line of inquiry in this area uses linear elastic fracture mechanics (LEFM). Ice is a notably brittle material: its fracture toughness is approximately 20% that of typical household glass, the latter typically held up as an example of an extremely brittle material. Recent observations from Antarctica have shown that ocean swell, infragravity waves, and tsunamis can trigger ice shelf rift propagation and calving (Bromirski et al., 2017, JGR, and works cited therein). To explain these observations, I have developed a theory of the stresses required to cause the fracture growth that leads to iceberg calving. Future work will focus on simplifications of this theory with an eye towards parameterizations for large-scale ice sheet models. I am not aware of any seismograms recorded on grounded calving termini, and field work may benefit our understanding of calving processes in this setting.