Seasonal trend in suspended-sediment transport from an Arctic glacier, and implications for drainage-system structure

Abstract

Suspended-sediment concentration (SSC) and discharge time series have been obtained for a proglacial stream draining from Scott Turnerbreen, a non-temperate glacier at 78° N in the Svalbard archipelago. These time series exhibit seasonal trends in diurnal hysteresis between SSC and discharge, which changes progressively from clockwise (SSC lead) to anticlockwise (SSC lag), and in the availability of sediment for fluvial transport, which increases during the season. These results contrast with those for streams draining temperate glaciers, in which a seasonal trend in diurnal hysteresis is typically not observed, and sediment supply is usually exhausted during the melt season. This contrast indicates differences in the processes of sediment acquisition and in temporal patterns of sediment transport between temperate and non-temperate glaciers, which reflect different drainage-system structures. The principal mechanism of suspended-sediment acquisition by meltwater is subaerial sediment supply to ice-marginal channels at non-temperate glaciers, whereas at temperate glaciers it is subglacial supply to basal channels. The hysteresis trend probably arises from a delaying effect, because of sediment circulation in pools and slack water adjoining the ice-marginal channels, which varies with discharge. Continuing subaerial sediment supply from heavily debris-covered ice-cored moraines during the melt season precludes sediment-supply exhaustion at Arctic glaciers but means that measurements of sediment flux give a misleading indication of the contemporary rate of glacial erosion.