Interior Ice-Sheet Dynamics are Constrained through the Holocene Transition using the Thermodynamics of South Pole Lake

Abstract:

Most studies on subglacial environments have focused on either active lakes under West Antarctic ice streams or especially large lakes in East Antarctica; however, the majority of Antarctic subglacial lakes are actually small water bodies under thick ice in East Antarctica. These lakes may hold clues to the history of the much older and larger eastern half of the Antarctic Ice Sheet. Here, we present the most extensive geophysical exploration to date of one such East Antarctic lake near the geographic South Pole, which is underlain by a 100-meter thick sediment column, making it a prospective site for sediment coring. Our horizontal and vertical strain measurements indicate that basal sliding may be occuring, consistent with a regionally thawed bed. Further, the strain rates are out of balance, which could indicate a recent change in basal thermal state (onset of sliding) to which the ice sheet has yet to equilibrate. Nearby measurements of ice temperature made at the IceCube Array in ’07-’10 are colder than would be expected for a bed that remained thawed through the Holocene and into the most recent glacial period. We use a 1-dimensional thermal model, optimized with the IceCube measurements, to invert for the geothermal flux, sliding, and deformational heat sources through time. The model is constrained with historical surface temperature and accumulation data from the South Pole Ice Core. Our result favors two possible scenarios that are consistent with the measured temperature profile: first, as has been suggested by previous authors, a slowdown in ice flow and associated drop in basal shear heating due to a cessation of basal sliding could explain the exceptionally cold conditions with a freezing lake that is a relic from a prior time; second, a speedup in ice flow could have initiated basal melting during the Holocene transition with the IceCube Array remaining cold because of the long thermal diffusion timescale in ice. Based on our geophysical data, we hypothesize that ice in the South Pole region sped up through the Holocene transition and that the South Pole Lake formed (or more likely reformed) during the Holocene.