Characterization of dissolved and particulate organic matter exported during late summer from a glacio-nival river, Zackenberg, Greenland

• Main Authors: Fouche Julien, Hirst, Catherine, Opfergelt, Sophie, Vonk Jorien, Bonneville Steeve, Haghipour Negar, Eglinton Timothy, Broder Lisa, EGU General Assembly 2020
• Other Authors: UCL - SST/ELI/ELIE - Environmental Sciences
• Format: Conference Object
• Language: English
• Published: 2020
• Subjects: Arctic; Greenland; glacier; Global warming; Ice; permafrost; Thermokarst; Zackenberg
• Online Access: http://hdl.handle.net/2078.1/239916

W ith Arctic warming, both gradual and abrupt thaw of permafrost may trigger a positive feedback loop, since large amounts of organic matter (OM) are released into rivers and thus exposed to mineralization along the fluvial continuum. Both dissolved (DOM) and particulate organic matter (POM) mineralization during lateral transport generates greenhouse gases that may fuel further global warming. In addition to glacier retreat, the extent of permafrost thaw is predicted to increase across the Arctic, which will change the release of DOM and POM to aquatic environments. However, the fate of DOM and POM will likely differ during transport in surface waters due to POM-DOM exchange and biodegradation control from organo-mineral interactions. The contrasting behavior between POM and DOM may affect the strength of the permafrostcarbon feedback to climate but is currently afflicted with high uncertainties. This study characterizes the export of DOM and POM along the fluvial continuum at time of maximum thaw depth and investigates the impacts of permafrost thaw on OM composition and age in the Zackenberg watershed (Northeastern Greenland). In August 2019, streams were sampled twice, before and after a rain event. We collected water and suspended sediments from rivers, the river delta, snow patches and permafrost ice from thermokarst features. Besides in situ river chemistry, we analyzed stable water isotopes (δ18O, δ2H) and dissolved organic carbon (DOC) concentrations. The composition of DOM was characterized using absorbance and fluorescence spectroscopy and both DOM and POM were analyzed for radiocarbon (Δ14C). DOC concentrations increase from 3.1 mg L-1 upstream to 15.6 mg L-1 after the confluence with the main tributaries, which are characterized by a nival river regime, and decreased to 4.3 mg L-1 at the outlet. Optical properties of DOM highlight that low molecular weight microbial-derived organic compounds contribute most to the fluorescent DOM (fDOM) in the upstream part of the river, likely originating from ...