Weekly CASPO Seminar: Join us in Nierenberg 101 every Wednesday at 3:30 pm to hear about the latest and greatest in Climate, Atmospheric Sciences, and Physical Oceanography!
Jeff Severinghaus will give a talk titled "Episodes of chaotic mechanical disruption of the firn layer (snowpack) at 6 warm times in the past 100,000
years at Siple Dome, Antarctica: Signals of past West Antarctic Ice Sheet groundling-line retreat events?"
How much, and how fast, sea level will rise in the next few centuries is an urgent question for
humanity. An important source of uncertainty in projections comes from the poorly understood
nature of unstable ice sheet-ocean interaction that can lead to rapid sea level rise. Here I discuss
an enigmatic data set from the Siple Dome ice core, drilled in 1997-1998. Siple Dome is an ice
dome flanked by the fast-flowing West Antarctic ice streams, and the core was drilled in order
to probe the ice-dynamical behavior of the West Antarctic Ice Sheet over the last glacial cycle.
The ice core showed six separate events of firn fracturing and disruption, seen in multiple gas proxies
of firn air convection, direct visual inspection of the core, layer-imaging electrical conductivity data, and
borehole-laser logs as anomalously reflective intevals of a few meters attributed to excess air bubble
density from “healed" fractures or crevasses. All six occur during times of warming climate. Recent 14C
evidence from subglacial drilling of the ice streams shows that an incursion of marine waters and
14C-containing organisms happened in the last 11 kyr (Kingslake et al., 2018). These observations
can be explained if the marine grounding line (the point where grounded ice transitions to floating ice shelves)
retreated upstream underneath Siple Dome, which is currently 50 km from the grounding line,
releasing all basal friction as the ice went afloat, and therefore causing a rapid thinning and
mechanical disruption of the ice as the grounding line passed beneath the summit of Siple Dome.
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