THE HYDROCHEMISTRY OF MELTWATERS DRAINING A POLYTHERMAL-BASED, HIGH ARCTIC GLACIER, SOUTH SVALBARD - I - THE ABLATION SEASON

Solute and runoff time-series at Finsterwalderbreen, Svalbard, provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments. The hydrochemistry of a subglacial upwelling provides evidence for a snowmelt-fed subglacial reservoir that dominates bulk runoff during re cession flow. High concentrations of Cl- and crustal ions, high pCO(2) and ratios of [SO42-/(*SO42- + HCO3-)] close to 0.5 indicate the pas sage of snowmelt through a subglacial weathering environment character ized by high rock:water ratios, prolonged residence times and restrict ed access to the atmosphere. At higher discharges, bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conve yed through a chemical weathering environment characterized by low roc k:water ratios, short residence times and free contact with atmospheri c gases. These observations suggest that icemelt is routed via a hydro logical system composed of basal/ice-marginal, englacial and supraglac ial components and is directed to the glacier margins by the ice surfa ce slope. Upwelling water hows relatively independently of icemelt to the terminus via a subglacial drainage system, possibly constituting f low through a sediment layer. Cold basal ice at the terminus forces it to take a subterranean routing in its latter stages. The existence of spatially discrete flow paths conveying icemelt and subglacial snowme lt to the terminus may be the norm for polythermal-based glaciers on S valbard. Proglacial mixing of these components to form the bulk meltwa ters gives rise to hydrochemical trends that resemble those of warm-ba sed glaciers. These hydrochemical characteristics of bulk runoff have not been documented on any other glacier on Svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology. (C) 1998 John Wiley & Sons, Ltd.