Quantifying the magnitude, spatiotemporal variation and age of aquatic CO2 fluxes in western Greenland

Abstract:

High latitude regions are experiencing accelerated atmospheric warming, and understanding the terrestrial response to this is of crucial importance as: a) there is a large store of carbon (C) in permafrost soils which may be released and feedback to climate change; and, b) ice sheet melt in this region is accelerating, and whilst this will cause albedo and heat flux changes, the role of this in atmospheric gas release is poorly known. To understand how sensitive arctic environments may respond to future warming, we need measurements that document current C flux rates and help to understand C cycling pathways.

Although it has been widely hypothesised that arctic regions may become increasingly significant C sources, the contribution of aquatic C fluxes which integrate catchment-wide sources has been little studied. Using a floating chamber method we directly measured CO₂ fluxes from spatially distributed freshwaters (ice sheet melt, permafrost melt, and lakes/ponds) in the Kangerlussuaq region of western Greenland during the early part of the summer 2014 melt season. Fluxes from freshwaters with permafrost sources were in the range -3.15 to +1.28 µmol CO₂ m^-2 s^-1. Fluxes from a river draining the ice sheet and the Russell Glacier were between -2.19 and +4.31 µmol CO₂ m^-2 s^-1. These ranges show the systems can be both sources (efflux) and sinks (influx) of CO₂. Most freshwater data worldwide shows CO₂ efflux and so recording aquatic systems being a CO_{2­ ­}sink is unusual. Our data show spatial and temporal variations that are related to hydraulic as well as biogeochemical processes.

Additionally, where we recorded CO₂ efflux we collected effluxed CO₂ for radiocarbon analysis. The measured age of the released gas will help to identify the sources and dominant transport processes of CO­₂ (e.g. entrained modern atmospheric CO₂, or old CO₂ trapped during ice formation released through ice melt, or CO₂ derived from respiration of soil and sediment organic matter). These samples are currently being analysed and we intend to present this original data at AGU. By directly measuring aquatic CO₂ efflux and age from this climatically sensitive arctic location and quantifying drawdown in high-pH ice melt streams, we have a unique dataset that aids understanding of key feedbacks affecting the impact of projected future climate change.