Subglacial drainage across Kamb Ice Stream’s Grounding Zone, West Antarctica.

Kamb Ice Stream in West Antarctica is a poster child for the natural variability of ice sheet flow. This major ice stream ceased flowing approximately 160 years ago and mass gain in its catchment currently offsets a significant portion of the mass loss occurring elsewhere in West Antarctica. Hypotheses explaining why Kamb shut down include changes in water routing at the ice stream bed. Here I report on our exploration of the main subglacial drainage channel crossing Kamb’s grounding zone and entering the ocean cavity beneath the Ross Ice Shelf. We find that the subglacial channel transitions into a large sub ice shelf channel. Oceanographic observations detect subglacial discharge within the channel, although the channel shape and surface elevation change suggest greater discharge rates in the past. Sediment coring of the channel substrate shows evidence of repeated high-velocity discharge events. The provenance of these sediments, combined with subglacial routing constraints indicate the subglacial catchment varies in time. Together with observations of surface change, these findings indicate that the subglacial hydrologic network beneath Kamb Ice Stream varies temporally, with background flow punctuated by fast flow events, and also changes spatially, spanning catchments of variable size.