Details

Autor(en) / Beteiligte

• Graly, Joseph A.
• Drever, James I.
• Humphrey, Neil F.

Titel

Calculating the balance between atmospheric CO 2 drawdown and organic carbon oxidation in subglacial hydrochemical systems

Ist Teil von

• Global biogeochemical cycles, 2017-04, Vol.31 (4), p.709-727

Erscheinungsjahr

2017

Link zum Volltext

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Abstract In order to constrain CO 2 fluxes from biogeochemical processes in subglacial environments, we model the evolution of pH and alkalinity over a range of subglacial weathering conditions. We show that subglacial waters reach or exceed atmospheric p CO 2 levels when atmospheric gases are able to partially access the subglacial environment. Subsequently, closed system oxidation of sulfides is capable of producing p CO 2 levels well in excess of atmosphere levels without any input from the decay of organic matter. We compared this model to published pH and alkalinity measurements from 21 glaciers and ice sheets. Most subglacial waters are near atmospheric p CO 2 values. The assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies. If the subglacial environment is assumed to be closed from any input of atmospheric gas, large organic carbon inputs are required in nearly all cases. These closed system assumptions imply that order of 10 g m −2 y −1 of organic carbon are removed from a typical subglacial environment—a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon. Partial open system input of atmospheric gases is therefore likely in most subglacial environments. The decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock. In glaciers and ice sheets on silicate bedrock, substantial long‐term drawdown of atmospheric CO 2 occurs. Key Points The subglacial waters of temperate ice have pH and alkalinities consistent with partial atmospheric gas exchange during chemical weathering Closed system sulfur oxidation following atmospheric gas exchange typically explains high p CO 2 values found in subglacial waters Drawdown of atmospheric CO 2 through silicate weathering typically exceeds CO 2 flux from organic matter decomposition in subglacial systems Plain Language Summary Two things can happen beneath a glacier or ice sheet: atmospheric carbon dioxide can be captured through chemical reactions with the underlying rock and carbon can be released to the atmosphere by decaying organic matter. This study finds that, in most cases, more carbon dioxide is captured than produced under ice. Carbon dioxide is a long‐lived, heat‐trapping gas whose influence on climate makes it a major controller in the growth and collapse of ice sheets over time. Glaciers that consume carbon dioxide through chemical weathering are helping maintain glacial conditions on Earth, whereas those that release carbon dioxide from organic matter are limiting them. This paper synthesizes data from 21 glaciers, analyzing the balance of atmospheric and organic carbon in each. Our analysis suggests that under most glaciers, more carbon dioxide is leaving the atmosphere through chemical weathering than entering from the decay of organic matter, but the scale of this effect depends on the type of rock underlying the ice. This differs from previous scientific work that postulated a more important role for organic carbon decay.