Seasonal hydrological cycle control on age, abundance and lability of carbon exported from the Greenland ice sheet
Abstract
Glacial environments possess a more dynamic organic carbon system than previously thought. The discovery of abundant, active microbial communities at the base of glaciers and ice sheets provides a mechanism for both (a) extensive subglacial organic carbon metabolism (e.g. respiration, fermentation) on various timescales, and (b) the present-day export of labile carbon to downstream ecosystems. Prior studies are limited but point towards the importance of both of these processes in modulating carbon cycling. In order to develop predictive understanding of these processes, elucidation of the dominant molecular-level and bulk carbon dynamics is critical. Here we build on earlier results that described changes in molecular-level composition of dissolved organic matter associated with the Greenland ice sheet (GrIS), by describing for the first time the bulk-level carbon composition of glacial meltwater from the GrIS. Our study focuses on several outlet glaciers and a large proglacial lake along the western margin of the GrIS. We investigate the organic carbon abundance (dissolved and particulate concentrations), age (dissolved and particulate radiocarbon content), and lability (dissolved organic carbon to nitrogen ratios) in the subglacial discharge throughout the summer melt season. The early season (May) glacier discharge contains significantly higher dissolved organic carbon concentrations (23 - 342 μM), and exports younger carbon (~ 2 kyr 14C age) compared to the peak season (July) glacier discharge, where the concentrations are lower (11 - 51 μM) and the age is older (~ 4 kyr 14C age). These results illustrate (1) that chemically-distinct organic carbon pools are accessed by seasonally-evolving hydrological flow-paths and (2) that the GrIS can deliver labile, old carbon to the North Atlantic and Arctic Oceans.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B21F..03B
- Keywords:
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- 0793 CRYOSPHERE / Biogeochemistry