Mitchell, A. C. and Brown, G. H. (2008)
Modeling geochemical and biogeochemical reactions in subglacial environments
Article
- Cite key
- Mitchell2008
- Language
- en
- Journal
- Arctic, Antarctic, and Alpine Research
- Volume
- 40
- Number
- 3
- Pages
- 531-547
- URL
- http://www.bioone.org/doi/pdf/10.1657/1523-0430(06-075)[MITCHELL]2.0.CO;2
- Description
- This study examines current subglacial biogeochemical weathering models using
PHREEQCi, a computer-based speciation mass-balance (SMB) model, parameterized using hydrochemical and mineralogical field data from Haut Glacier d’Arolla,
Switzerland. The aim is to investigate the utility of SMB models for quantifying
subglacial biogeochemical mechanisms, and the mathematical and thermodynamic
robustness of current subglacial weathering models in a temporally variable, spatially
heterogeneous hydrological and geochemical subglacial environment.
The chemical evolution of meltwaters between their source in the supraglacial
environment and their output from the hydroglacial system as bulk meltwaters are
modeled, and compared with in situ meltwaters collected from the base of boreholes
drilled to the glacier bed. SMB modeling produced a broad range of weathering
outcomes, but delivered no unique weathering scenario which could account for the
observed changes in water chemistry between input and output waters over the
ablation season. Organic carbon oxidation and sulfide oxidation by dissolved O2,
coupled to carbonate dissolution and incongruent silicate dissolution, could account
for seasonal changes in meltwater chemistry, supporting current subglacial
biogeochemical weathering models. Atmospheric CO2 was not required under any
weathering scenario, and organic carbon and atmospheric CO2 dissolution was only
possible in one weathering scenario, at a mass ratio of 10:1, further suggesting that
CO2-driven dissolution is unimportant in subglacial environments. This investigation
indicates the utility of SMB models applied to subglacial hydrological systems for
determining geochemical and biogeochemical processes and interpreting water
quality.