Subglacial swamps

Abstract

The existence of both water and sediment at the bed of ice streams is well documented, but there is a lack of fundamental understanding about the mechanisms of ice, water and sediment interaction. We pose a model to describe subglacial water flow below ice sheets, in the presence of a deformable sediment layer. Water flows in a rough-bedded film; the ice is supported by larger clasts, but there is a millimetric water layer submerging the smaller particles. Partial differential equations describing the water film are derived from a description of the dynamics of ice, water and mobile sediment. We assume that sediment transport is possible, either as fluvial bedload, but more significantly by ice-driven shearing and by internal squeezing. This provides an instability mechanism for rivulet formation; in the model, downstream sediment transport is compensated by lateral squeezing of till towards the incipient streams. We show that the model predicts the formation of shallow, swamp-like streams, with a typical depth of the order of centimetres. The swamps are stable features, typically with a width of the order of tens to hundreds of metres.

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

“…The findings of Oswald & Robin [2] substantiated the theory of persistent subglacial water in Antarctica and also led to speculation that these lakes might provide refuge for microorganisms. It is now accepted that there are a variety of aqueous features beneath ice sheets including 'wetlands' or saturated sediments, streams, rivers and lakes [3,4]. As of this writing, 379 perennial subglacial lakes have been identified below the Antarctic ice sheets [5] and these lakes likely represent a variety of chemistries ranging from fresh [6,7] to highly saline [8,9].…”

“…This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH 4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor influence from seawater.…”

Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet

“…Therefore, a coupled distributed and channelized system that takes into account both porous flow through sediment and/or cavities is needed to properly address this problem in the future. Additionally, the definition of what is a subglacial lake has been expanding in recent years to include ponds and swamps [56,57], and 'ribbed terrane' [58] and even change in storage of subglacial aquifers [17]. Although these means of water storage comprise important parts of the subglacial environment, their evolution and stability on longer time scales is unclear.…”

Modelling water flow under glaciers and ice sheets

“…Model simplifications include the assumption of temperate bed conditions and partial treatment of thermal processes (such that energy is not conserved), the use of idealized domain geometry, omission of sediment transport (including by till deformation) and a limit on water depth to prevent N = 0. When sediment transport is added to the model [79], wide and shallow stable waterways develop through the combined effects of fluvial transport and shearing and squeezing of the saturated till.…”