Abstract
Chemical weathering dynamics in Greenland Ice Sheet (GrIS) catchments are largely unknown, due to a scarcity of field data. This paper presents the most comprehensive study to date of chemical weathering rates from four GrIS catchments of contrasting size. Cationic denudation rates varied greatly between catchments studied (2.6 to 37.6 tons km-2 a-1, world mean = 11.9 tons km -2 a -1), but were of the same order of magnitude to the world non-glacial riverine mean, and are greater than those documented in some major temperate rivers catchments (e.g. Mississippi (1.3 tons km-2 a-1) and Nile (0.4 tons km-2 a-1) rivers). These high chemical denudation rates indicate that the GrIS is a potential source of solute to downstream environments. Dissolved silica yields, indicative of silicate weathering rates, also varied by an order of magnitude, with upper values similar to the world mean (0.2 to 3.8 tons km-2 a-1, world mean = 3.53 tons km-2 a-1). Elevated chemical weathering rates in GrIS catchments are strongly influenced by the specific discharge, which drives flushing of the subglacial environment and physical erosion of the ice sheet bed. The direct relationship between specific discharge and chemical denudation rates supports the hypothesis that Greenland Ice Sheet chemical weathering rates and solute fluxes are likely to increase with enhanced melt rates in a warming climate.
Highlights
Rock-water chemical interactions control the solute concentration and composition of streams and rivers and play an important role in global biogeochemical cycles (Chillrud et al, 1994; Lasaga et al, 1994; Wadham et al, 2010b)
Annual yields of individual cations and Si and total cationic denudation rates from this study are plotted alongside previously published values from valley glaciers (Hodson et al, 2000; Wadham et al, 2000; Anderson, 2007), rivers draining non-glacierised catchments (Huh and Edmond, 1999) and major world rivers (Meybeck and Ragu, 2012) in a log-log scatter plot (Figure 2)
Annual cationic denudation rates in Greenlandic glacial catchments (2.6–37 tons km−2 a−1, Table 2) generally fall within the rage of values reported for other glaciated catchments and non-glaciated catchments (e.g., Siberian Rivers, Huh and Edmond, 1999)
Summary
Rock-water chemical interactions control the solute concentration and composition of streams and rivers and play an important role in global biogeochemical cycles (Chillrud et al, 1994; Lasaga et al, 1994; Wadham et al, 2010b). Carbonate dissolution in alpine glacial systems exceeds silicate dissolution in a ratio of 5:1 (Tranter et al, 2002c), compared to the global mean of 1.3:1 (Holland, 1978) This is because comminution of bedrock by physical erosion exposes trace carbonates, which display rapid dissolution kinetics (Anderson et al, 1997). Despite the predominance of carbonate weathering in glacial systems, it is possible that silicate mineral weathering is enhanced under certain hydrological conditions, such as within long residence time distributed subglacial drainage systems (Brown, 2002; Tranter et al, 2002c; Wadham et al, 2010b; Hawkings et al, 2017, 2018) This may influence the capacity for glacial systems to act as a source of crustal nutrients commonly associated with bedrock weathering such as Fe, Si, and P (Calvaruso et al, 2006; Hawkings et al, 2015)
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