Atmosphere Ocean Science Colloquium
Water, crevasses, and glacier dynamics in Southeast Greenland
Speaker: Prof. Kristin Poinar, University at Buffalo
Location: Warren Weaver Hall 1302
Date: Wednesday, November 15, 2023, 3:30 p.m.
Synopsis:
Helheim Glacier discharges ~30 Gt/yr of ice into the ocean, the water-equivalent of an Olympic swimming pool every three seconds. A combination of underlying topography, ocean forcing at its terminus, and the structure of the subglacial hydrologic system give rise to seasonal and interannual variability in the flow of this key Southeast Greenland glacier.
Helheim Glacier is unusual in that it has a far-upstream water source to its bed: firn aquifers, liquid water bodies buried 10-20 meters below the surface. Meltwater trickles downward through isothermal snow into these aquifers, then flows laterally downslope for tens of kilometers into crevasses. The integration of small amounts of melt across a wide area drive the fracture of crevasses to the bed hundreds of meters below. Without the aquifers to amass melt, the crevasses would arrest high in the ice column, and no melt would reach the bed.
Through field analysis, remote sensing, and modeling, we tested the effect of time-variable drainage of firn aquifer water on Helheim ice flow velocity. A fracture mechanics approach shows that crevasses access and drain the aquifer, and a simple box model with outflow through crevasses explains airborne observations of the water table well. Empirical orthogonal function (principal component) analysis of satellite-observed ice velocity shows that the flow of the glacier is quite variable in space and time and is sensitive to conditions at the terminus. The ice flow is modulated by subglacial hydrology, including water from the firn aquifer and frictional melting from glacier sliding. Observations from on-ice GPS stations suggest that water reaches the bed seasonally at our field site, 40 km from the glacier terminus and 1500 m above sea level. This is farther inland and higher on the ice sheet than typically assumed.
Independent observations near the terminus of Helheim Glacier indicate a threat of significant ice flow and retreat this century. The acceleration will depend on the subglacial hydrologic system and its ability to rapidly adapt to changes in overburden pressure and water inputs. The results of our study suggest that this will help stabilize the glacier, but its ultimate fate remains a function of the strength of the coming climate forcing.