Circulation and thermodynamics in a subglacial geothermal lake under the Western Skaftá cauldron of the Vatnajökull ice cap, Iceland

Abstract

[1] The subglacial, geothermal lake beneath the Western Skaftá cauldron (depression) in the Vatnajökull ice cap, Iceland, was accessed by hot water drilling through the overlying 300 m-thick ice shelf. Most of the ca. 100-m water column was near 4.7°C, but was underlain by a distinct $10 m-deep water mass at 3.5°C. The sensible heat content of the lake water is approximately twice the potential energy dissipated in outburst floods, and the temperature of the lake may be an important factor in the development of subglacial water courses of jökulhlaups from the lake. The lake temperature is higher than the temperature of maximum density, implying that convective heat transfer can take place in the lake. The vertical temperature structure suggests a large-scale recirculating flow in the lake, the rate of which was estimated from the lake temperatures and the chemical composition of a water sample. Citation: Jóhannesson, T.,

Microbial communities in the subglacial waters of the Vatnajökull ice cap, Iceland

“…However, in addition to biological sulfur cycling, sulfate can be formed by abiotic sulfide oxidation and SO 2 disproportionation, and removed by dilution with glacial melt. The Skaftárketill lakes contain volcanic CO 2 and presumably Fe(III) (in mafic minerals), and we are also reasonably certain that O 2 enters the lakes as the overlying ice shelf melts but have not detected it, probably because it reacts with sulfide to sub-micromolar levels on the B1-year residence time of the lakes (Jó hannesson et al, 2007). Although, we expect H 2 from serpentinization and we detected it in the west lake, we have been unable to quantify this sparingly soluble gas because of loss to bubbles during depressurization of retrieved samples.…”

“…There is no indication of a colder bottom water mass as in the west lake (Jó hannesson et al, 2007), but a single profile beneath borehole A contains some suggestion of this phenomenon. Like the west lake, all east lake samples were anoxic, with average sulfide (H 2 S) of 16 p.p.m., and average dissolved CO 2 of 105 p.p.m.…”

“…), cold (o5 1C) and low in organic matter (o o1 mg l À 1 C) owing to melting of the overlying, nutrient-poor ice (Á gú stsdó ttir and Brantley, 1994;Gaidos et al, 2004;Jó hannesson et al, 2007;Gaidos et al, 2009). The Grímsvötn lake was sampled in June 2002, 3 months after a jö kulhlaup, and consisted of oxygenated glacial melt, but the west Skaftárketill lake, explored in June 2006, was anoxic and sulfidic, with hydrothermal input (Jó hannesson et al, 2007). The pelagic microbial communities are also distinct: Grímsvö tn contains a low abundance (2 Â 10 4 cells ml À 1 ) of diverse heterotrophic bacteria (Gaidos et al, 2004), whereas west Skaftárketill has a higher biomass (5 Â 10 5 cells ml À 1 ) dominated by a few bacterial taxa related to anaerobes and microaerobes, with no evidence for archaea (Gaidos et al, 2009).…”

“…), cold (o5 1C) and low in organic matter (o o1 mg l À 1 C) owing to melting of the overlying, nutrient-poor ice (Á gú stsdó ttir and Brantley, 1994;Gaidos et al, 2004;Jó hannesson et al, 2007;Gaidos et al, 2009). The Grímsvötn lake was sampled in June 2002, 3 months after a jö kulhlaup, and consisted of oxygenated glacial melt, but the west Skaftárketill lake, explored in June 2006, was anoxic and sulfidic, with hydrothermal input (Jó hannesson et al, 2007).…”

Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain

“…3). Similarly, sample E7 comes from a river that occasionally drains subglacial geothermal lakes under the western Vatnajökull glacier (Johannesson et al, 2007).…”