A gaining and losing meltwater corridor in the subglacial environment

Abstract:

Meltwater transmission beneath glacial systems is a fundamental consideration for understanding ice-bed conditions and thus bed-modulated ice flow, with potential impacts on terminus behavior through, for example, impacts on sediment delivery to grounding lines. Realistically characterizing subglacial hydrology relies on knowing the range of possible drainage styles and their spatiotemporal evolution. We present a paleo-subglacial meltwater corridor (5-km wide, >60-km long) comprised of at least 73 Nye-type channels preserved on the deglaciated Antarctic continental shelf. Upstream to downstream (i.e., along-ice flow) transitions in convergence and divergence of meltwater occurred through discrete channels ranging from <1-16 km in length and <2-33 m deep. The corridor encompasses a mixture of blind channels (i.e., with no obvious water source at the channel head), channel braiding, and an extensive meander segment. Bank-full channel area – an approximation for meltwater drainage capacity – varies three orders of magnitude along the length of the corridor, signifying additions of basal water to the channelized drainage system, that correspond to changes in bed topography. A loss of channelized water ~10 km from the apparent terminus of the corridor, likely occurred due to intersections between the channelized drainage system and a shallow groundwater system as water drained through sediment pore spaces. Sedimentological evidence indicates there is channel-siphoning of surrounding sediment pore water, as well as co-mingling of channelization and Darcian flow in the downstream-most segment that remains capable of enhancing sediment flux to the grounding line.