Two Metrics Describing the Causes of Seasonal and Spatial Changes in Subglacial Aqueous Chemistry

Graly, Joseph, Humphrey, Neil F. and Licht, Kathy J. (2018) Two Metrics Describing the Causes of Seasonal and Spatial Changes in Subglacial Aqueous Chemistry. Frontiers in Earth Science, 6. pp. 1-8. ISSN 2296-6463

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Official URL: https://doi.org/10.3389/feart.2018.00195

Abstract

Seasonal change in surface melt input and spatial controls on the distribution of subglacial water can cause considerable variability in the aqueous chemistry of subglacial waters. Much of this variability has been interpreted in terms of a single variable: water residence time, with slow flow assumed to correlate with greater mineral dissolution and oxidative weathering. We synthesize data from a range of glacier and ice sheet settings to show that this approach does not adequately describe presently available data. Instead, we propose that two independent variables control spatial and seasonal changes in aqueous chemistry in subglacial settings: atmospheric gas abundance and sediment supply abundance. Where atmospheric gases are abundant, carbonation weathering is responsible for most of the subglacial chemical activity; where they become limited, oxidation weathering becomes more dominant. Where freshly comminuted sediment is abundant, easily dissolved minerals, especially calcite, have proportionally more influence on subglacial hydrochemistry; where sediment supply is limited, silicate minerals, and less reactive carbonate minerals will increase in relative influence. In most settings, simple metrics of the abundance of SO42− and Ca2+ in the subglacial waters can characterize these two variables. In the data we synthesize, neither variable consistently correlates to the inferred water residence time, nor do the variables consistently correlate with each other. Spatial data show that point locations and small catchments on the glacial bed differ substantially from the integrated composition found at glacial outlets. The varied response in the subglacial aqueous chemistry to changing water residence times suggests complex control by a broad range of glaciological factors that affect water routing and subglacial sediment generation.

Item Type: Article
Uncontrolled Keywords: chemical weathering, subglacial hydrology, seasonal variation, glacial processes, hydrochemistry, Greenland ice sheet, svalbard, Alps-northern appennine
Subjects: F600 Geology
F700 Ocean Sciences
F800 Physical and Terrestrial Geographical and Environmental Sciences
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: Rachel Branson
Date Deposited: 09 Mar 2020 10:47
Last Modified: 09 Mar 2020 11:00
URI: http://nrl.northumbria.ac.uk/id/eprint/42412

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