Hydrology, microbiology and carbon cycling at a high Arctic polythermal glacier, (John Evans Glacier, Ellesmere Island, Canada).

摘要

Analysis of the hydrology, hydrochemistry and microbiology at polythermal John Evans Glacier and geochemical and isotopic data from Haut Glacier d'Arolla demonstrates that certain subglacial chemical weathering processes are microbially mediated.; Subglacial drainage is likely an annual occurrence beneath John Evans Glacier and solute rich subglacial waters indicate over winter storage at the glacier bed. Subglacial microbial populations are also present, and are viable under simulated near in situ conditions at 0.3°C. This suggests that temperate subglacial environments at a polythermal glacier, which are isolated by cold ice above and around them, provide a viable habitat for life where basal water and organic carbon are present throughout the year. Thus, a subglacial microbial ecosystem based upon legacy carbon, (from old soils or surface inputs) rather than primary production may exist, where redox processes are a key component, and seasonal anoxia may occur. The existence of anoxic environments is supported by the presence of strictly anaerobic bacteria (sulphate reducing bacteria and methanogens) in the basal sediments—which are viable in culture at 4°C—and also argues that these bacteria are not washed in with oxygenated surface meltwaters, but are present in the subglacial environment.; During the summer meltseason there is a large input of surficial waters to the subglacial system and water residence times are drastically reduced. Hence, kinetic weathering processes dominate, resulting in light δ 13C-DIC (dissolved inorganic carbon) in glacial runoff, as verified by experimental work on CaCO₃ and John Evans Glacier sediments. The experiments demonstrate kinetic bedrock fractionation (KBF) during carbonate hydrolysis and that kinetic fractionation of CO₂ (KFC) is proportional to the rate of CO₂ draw down during the carbonation of carbonates. This results in significantly depleted δ13C-DIC values (≤−16 ‰) relative to the bedrock carbonate. Incorporating KBF and KFC processes into geochemical weathering models makes it possible to distinguish between kinetic effects and microbial CO₂ as causes of light δ13C-DIC in glacial runoff. However, where kinetically produced DIC dominates, this can potentially mask small microbial respiration signatures. Only in the distributed system waters at Haut Glacier d'Arolla is light δ13C-DIC clearly due to microbial respiration.