Direct effect of ice sheets on terrestrial bicarbonate, sulphate and base cation fluxes during the last glacial cycle: minimal impact on atmospheric CO2 concentrations

Abstract

Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are f 25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO 2 . The potential change in atmospheric CO 2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being < 1 ppm. D

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

“…Of all analyzed variables, cation yield is most highly correlated with the proportion of glacial cover and the sampling distance from the glacial snout (SI Appendix, Table S3). Subglacial weathering fluxes also depend on hydrology, for example, differing for warm-vs. coldbased ice (35,36) and along different flowpaths (37), and these differences may explain some of the variability within the dataset.…”

“…Driving all oxidation by atmospheric O 2 would consume 5-14 × 10 11 mol O 2 /y, or 5-14 × 10 15 mol O 2 over 10 ky, less than 0.01-0.04% of the atmospheric reservoir of ∼4 × 10 19 mol O 2 and within the range of observed declines in pO 2 over the past 1 My (46). Similarly, proxies or models of total weathering fluxes to the oceans (36,47,48) may not capture modest increases in these sulfate fluxes because oxidative weathering is a small portion of the total global weathering flux.…”

Clay mineral precipitation and low silica in glacier meltwaters explored through reaction-path modelling

“…Anderson and others 1997;Lafreniere and Sharp, 2005; Pogge von Strandmann and others, 2006; Wimpenny and others, 2011), and the relevant impacts on atmospheric CO 2 drawdown (e.g. Sharp and others, 1995a; Hodson and others, 2000;Tranter and others, 2002a). More recent work has shifted the focus of subglacial weathering to consider the importance of alternative proton sources for mineral dissolution through microbially mediated pyrite oxidation and organic carbon sources, because atmospheric CO 2 and O 2 supply are often limited at the glacier bed (e.g.…”

Geochemical characteristics of meltwater and pondwater on Barton and Weaver Peninsulas of King George Island, West Antarctica

“…The concentrations of the Ca, Mg and Na of the soils were lower than those of the rocks. This result may be associated with carbonate mineral dissolution and alteration of silicate minerals (Tranter et al, 2002;Wadham et al, 2007). However, the K concentrations of the soils were higher than those of the rocks, which may be attributable to the accumulation of K + from sea salt.…”