Imaging an Englacial Brine Conduit within a -17°C Polar Glacier

Abstract:

Despite cold ice, there is evidence of an active zone of englacial brine that taps the subglacial brine reservoir of Taylor Glacier, McMurdo Dry Valleys (average annual air temperature -17°C). As part of the MIDGE (Minimally Invasive Direct Glacial Exploration) project, our geophysical study aims to reveal the hydraulic path of brine through Taylor Glacier prior to surface discharge at Blood Falls. We collected ground-penetrating-radar surveys at the terminus of Taylor Glacier that show a horizontal, linear scattering zone, the first evidence for englacial brine near Blood Falls. The scattering zone extends from Blood Falls upglacier and its trend matches that of past brine discharge cracks. By measuring depression of the basal ice reflector, we estimate a > 4% liquid brine content at the edge of the englacial scattering zone, assuming even dispersal of water within the ice column extending from the top of the scattering zone to the basal reflector. The brine content likely increases towards the center of the scattering zone as the underlying, depressed basal reflector disappears altogether. The concentration of brine at the center of the scattering zone may involve processes such at cryoconcentration and active input of brine from a nearby source. We use hydraulic potential models to map the source pathway of the englacial brine; the glacier’s significant surface relief drives channelization of subglacial fluids. On the northern side of the eastward flowing glacier, channeled fluids are trapped between ice-cored moraines to the north and east and an area of high hydraulic potential to the south. The trapped fluids pond beneath and upglacier from Blood Falls and provide a likely source pool for the observed englacial brine. Although Blood Falls is a unique feature, our results suggest that polar glaciers can support subglacial and englacial hydraulic systems despite a temperature difference between the ice and the brine of nearly 10°C.