The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skaftá river, Iceland

Abstract

This study describes the chemical composition of dissolved, degased and suspended fluxes of the 2002 Skaftá glacial flood, which emerged from one of the Skaftá subglacial lake due to geothermal activity beneath the Icelandic Vatnajökull glacier. The dissolved and suspended fluxes during the flood are compared with those normally observed in the Skaftá river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters. Concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the Skaftá river. In addition, dissolved concentrations of nutrients such as SiO2, Fe, and V, increased more than an order of magnitude during the flood. These will affect biological processes on a local scale. The δ34S composition in the flood water suggests that the dissolved SO4 was derived from the oxidation of H2S and the geothermal fluid. The total suspended particulate load measured in the Skaftá river during the 8-day 2002 flood was approximately half of the non-flood total annual Skaftá suspended load. As particles carry the bulk of limiting nutrients to the oceans, this demonstrates the importance of glacial floods for primary production of coastal waters. The composition of the flood water and the Skaftá subglacial lake, together with reaction path modelling suggest that substantial degasing of CO2 and H2S occurred at the glacial outlet during the flood. This degasing may have released as much as 262,000 and 7,980tonnes of CO2 and H2S, respectively, to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event.