Subglacial silica deposits

Abstract

SUPERFICIAL carbonate deposits are common on bedrock surfaces recently exposed by retreating temperate glaciers^1–5. Their morphology indicates that they formed subglacially in intimate contact with sliding ice. Besides suggesting that chemical transport is an active subglacial process, these relatively widespread deposits reflect high solute concentrations in subglacial waters. This is a fact of considerable significance because solutes at the glacier–bed interface can impede significantly the sliding of temperate glaciers⁵. The dynamics of temperate glaciers and especially the more intriguing aspects of their behaviour, such as surging⁶, are thought to depend critically on the basal sliding process⁷. Thus, chemical exchange at the base of a glacier may affect significantly its entire motion. Moreover, because glacial erosion and deposition are largely dependent on glacial sliding, they too are affected by the presence of solutes at the bed. To date, reported subglacial deposits have all been carbonates. On the basis of previously unrecognised subglacial deposits rich in silica, I suggest that subglacial deposits are not exclusively carbonates, but that silicates are of wider significance, than is believed at present.