Abstract
Abstract. Ice streams are corridors of fast-flowing ice that control mass transfers from continental ice sheets to oceans. Their flow speeds are known to accelerate and decelerate, their activity can switch on and off, and even their locations can shift entirely. Our analogue physical experiments reveal that a life cycle incorporating evolving subglacial meltwater routing and bed erosion can govern this complex transitory behaviour. The modelled ice streams switch on and accelerate when subglacial water pockets drain as marginal outburst floods (basal decoupling). Then they decelerate when the lubricating water drainage system spontaneously organizes itself into channels that create tunnel valleys (partial basal recoupling). The ice streams surge or jump in location when these water drainage systems maintain low discharge but they ultimately switch off when tunnel valleys have expanded to develop efficient drainage systems. Beyond reconciling previously disconnected observations of modern and ancient ice streams into a single life cycle, the modelling suggests that tunnel valley development may be crucial in stabilizing portions of ice sheets during periods of climate change.
Highlights
Continental ice sheets currently store the equivalent of a 65 m thick global water layer and have been major contributors to the nearly 85 mm in global sea level rise measured between 1993 and 2017 (Vaughan et al, 2013; Beckley et al., 2015)
After an initial identical state, a six-stage ice stream life cycle linking outburst flooding, transitory ice streaming, and tunnel valley development has been observed for all these simulations (Figs. 2, 3)
The silicon stream, still channelized, still flows 8 times faster than the rest of the silicon layer and is still decoupled from the substratum. These results are consistent with inferences that channelization of hitherto distributed subglacial water drainage systems can occur and reduce ice flow velocity after outburst floods (Kamb, 1987; Retzlaff and Bentley, 1993; Magnússon et al, 2007), and it can be responsible for narrowing and deceleration of ice streams (Raymond, 1987; Retzlaff and Bentley, 1993; Catania et al, 2006; Beem et al, 2014; Kim et al, 2016)
Summary
Continental ice sheets currently store the equivalent of a 65 m thick global water layer and have been major contributors to the nearly 85 mm in global sea level rise measured between 1993 and 2017 (Vaughan et al, 2013; Beckley et al., 2015). Connections between ice stream activity and subglacial hydrology are supported by the occurrence of geomorphic markers of meltwater drainage on ancient ice stream beds (e.g. meltwater channels, tunnel valleys, eskers) (Patterson, 1997; Margold et al, 2015; Livingstone et al, 2016) Among these markers, tunnel valleys deserve specific attention because they have high discharge capacities and, as such, may be major contributors to the release of meltwater and sediment to the ocean and may promote ice sheet stability by reducing the lubricating effect of high basal water pressure. This study reconciles into a single story several detached inferences, derived from observations at different timescales and at different places on modern and ancient ice streams
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