Continental Ice Sheet Retreat, Chemical Weathering, and Isotope and Solute Fluxes: Examples from Western Greenland

• Main Author: Deuerling, Kelly M
• Language: English
• Published: University of Florida 2016
• Subjects: deglaciated; foreland; greenland; proglacial; strontium; weathering; Greenland; Carbonic acid; Ice Sheet
• Online Access: http://ufdc.ufl.edu/UFE0050586/00001

Since the Last Glacial Maximum, retreat of major continental ice sheets has exposed three distinct glacial foreland environments that include subglacial (beneath the ice), proglacial (draining water from the ice), and deglaciated (not connected to the ice) watersheds. This work documents distinct chemical weathering products associated with each of these watersheds based on chemical analyses of stream waters and bedload samples from five deglaciated and one proglacial watershed in western Greenland. Variations in the relative proportions of these watersheds as ice sheet advances and retreats will alter oceanic fluxes of solutes and isotopes, and atmospheric CO2 fluxes, which may preserve a record of past ice sheet dynamics and impact future carbon cycling. In inland deglaciated watersheds near the ice sheet, weathering of carbonate minerals dominates the chemical weathering signal, but silicate mineral weathering increases toward the coast. Weathering overall is predominantly driven by carbonic acid from carbon dioxide hydration, but sulfuric acid weathering increases and carbonic acid weathering decreases toward the coast as iron-sulfide minerals oxidize. This solute signature of more extensive chemical weathering is consistent with a decrease in dissolved strontium isotope ratios toward the coast. The proglacial watershed shows decreasing carbonate and increasing silicate weathering downstream. An increase in strontium isotope ratios downstream is attributed to increased biotite weathering, hydrologic exchange within sandurs, and/or the introduction of water with distinct isotopic compositions from a different proglacial tributary. Minimal seasonal variations in chemical weathering were observed through one melt season in an inland deglaciated watershed, but silicate weathering increased through the melt season in the proglacial watershed. The change in mineral weathering is again reflected in strontium isotope ratios, which are elevated early in the melt season similar to pore water values documented in the sandur but decrease through time to values similar to tributaries. These results indicate that spatiotemporal variations in weathering across the newly exposed landscape will complicate marine records of continental ice sheet melting and alter magnitudes of atmospheric carbon dioxide sources and sinks.