Suspended sediment fluxes in a high-Arctic glacierised catchment: implications for fluvial sediment storage

Suspended sediment fluxes from the 68 km(2) Finsterwalderbreen catchment in Svalbard were monitored intensively during the 1999 and 2000 melt seasons, at proximal and distal ends of a 4.2 km(2) proglacial area, which has been deglacierised during the twentieth century. Measured distal sediment fluxes correspond to total catchment denudation rates of 2700 +/- 710 t km(-2) year 1 (1999) and 1800 +/- 350 t km(-2) year(-1) (2000). Hourly net sediment flux time series (distal flux minus proximal flux, isolating change within the proglacial area itself) reveal that the proglacial area serves as both a source and a sink of sediment during different periods of the melt season, and that the majority of sediment evacuation from the area occurs during discrete episodes of enhanced meltwater discharge. The mean net flux from the proglacial area itself was -690 + 230 t km(-2) year 1 (1999) and 3800 + 1700 t km(-2) year 1 (2000). Therefore, in 1999 there was a net increase in sediment storage in the proglacial area (aggradation), and in 2000 there was a net decrease (denudation). The pattern of sediment storage change appears to be driven by the runoff regime, with net storage occurring during a year of relatively episodic sediment transport in which relative supply exhaustion occurs, and net release in a year of more sustained sediment transport when relative supply exhaustion is absent. Many more years' monitoring would be required for any trend to emerge from the large interannual variability in sediment yield. (C) 2003 Elsevier B.V. All rights reserved.