Subglacial conditions during and after stoppage of an Antarctic Ice Stream: Is reactivation imminent?

Abstract

Borehole observations from the base of the West‐Antarctic Ice Sheet (WAIS) reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of Kamb Ice Stream (KIS). This ice layer has formed over a time of several thousand years by freeze‐on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location. Analysis of samples and videos sequences from boreholes drilled to the bottom of KIS confirms that KIS‐stoppage was due to basal freeze‐on and that relubrication of the ice stream is well underway. These results further suggest that ice stream cyclicity may be shorter than expected (1000s of years) and that a restart of KIS may be imminent within decades to centuries.

Superimposition of ribbed moraines on a palaeo‐ice‐stream bed: implications for ice stream dynamics and shutdown

“…This sequence of inferred events fits with observations of contemporary ice streams which also show a switch from extensional to compressional flow regimes before and after ice stream stoppage (Vogel et al, 2005).…”

“…Our observations of prominent fractures and thrusting appear to suggest a stiffening of the till that previously contributed to the motion of the ice stream. One way that till could become stiffer would be to drain water from it, and direct observation of contemporary ice stream beds using boreholes suggests that basal freezing is an effective mechanism to accomplish this process (Vogel et al, 2005). If this was the case at the Dubawnt Lake Ice Stream bed, the presence of ribbed moraines reveals the locations that underwent basal freezing, prior to warm-based deglaciation.…”

“…Therefore, data collected from the exposed beds of palaeoice streams has the potential to provide valuable insights about subglacial conditions and processes, complementing those being obtained from under the bed of active ice streams (e.g. Tulaczyk et al, 2001;King et al, 2003;Vogel et al, 2005;Peters et al, 2007;Smith et al, 2007). The inferred strain history of sediments preserved on a palaeo-ice stream bed, for example, might assist in parameterising the basal conditions in ice stream models.…”

“…This interpretation is also consistent with the conjecture that the change from glacial lineations to ribbed moraines implies ice stream stoppage. It is well accepted that fast-flowing ice streams are associated with horizontal extension (at least in ice) and the example of the UpC ice bulge in West Antarctica's Ice Stream C indicates that this stress state switches to compression after stoppage (Vogel et al, 2005).…”

Provenance of Des Moines lobe till records ice-stream catchment evolution during Laurentide deglaciation

“…There would remain the potential to incorporate new material by drag-folding at horizons of contrasting strength or by freezing-on (e.g. Vogel et al 2005). Large decreases in speed that result where drainage exceeds water production or availability (Catania et al 2006) might have occurred at the margin where loss of subglacial water through tunnel valleys occurred (Hooke & Jennings 2006).…”