Contrasting Export of Particulate Organic Carbon From Greenlandic Glacial and Nonglacial Streams

• Published in: Geophysical research letters Vol. 49; no. 21
• Main Authors: Bröder, L., Hirst, C., Opfergelt, S., Thomas, M., Vonk, J. E., Haghipour, N., Eglinton, T. I., Fouché, J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-11-2022; American Geophysical Union
• Subjects: Algae; Carbon; Carbon 14; Carbon dioxide; Chemical precipitation; Climate; Climate change; Continental interfaces, environment; Creeks & streams; Environmental Sciences; Exports; Fluvial sediments; Fractionation; Gas production; Glaciation; glacier; Global Changes; Global warming; Greenhouse effect; Greenhouse gases; Greenland; Ice sheets; Marine environment; Marine sediments; Microorganisms; Minerals; Oil and gas production; Organic carbon; Organic matter; Organic soils; Particulate organic carbon; Permafrost; Precipitation; radiocarbon; Radiocarbon dating; Rainfall; River sediments; Rivers; Sciences of the Universe; Sediment; Sedimentary rocks; Sediments; Soil; Soil bacteria; Soil layers; Soil microorganisms; Soil mixtures; Soil organic matter; Stocks; stream; Streams; Summer rainfall; Translocation; Greenland
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL101210

On‐going shrinkage of Greenland's icecap, permafrost thaw, and changes in precipitation are exposing its landscapes to erosion and remobilization of ancient organic carbon (OC) held in soils and sedimentary rocks. The fate of this OC and potential feedbacks to climate are still unclear. Here, we show that the glacial Zackenberg river (Northeastern Greenland) exports aged particulate OC (POC, uncalibrated radiocarbon ages of ∼4,000 years). Many of the smaller periglacial streams affected by abrupt permafrost thaw transport substantially older POC (up to 32,000 years), especially with enhanced discharge following intense precipitation. Mineralogical analysis, and density and size fractionation of soils and both glacial and nonglacial river sediments reveal that OC is largely associated with phyllosilicate minerals, suggesting stabilization against microbial processing. Enhanced export of ancient, mineral‐associated OC as a consequence of summer rainfall may accelerate translocation of OC from terrestrial to marine environments, but could have limited consequences for climate.
Plain Language Summary
On‐going Arctic warming leads to shrinking ice sheets and permafrost thaw, which promotes erosion of ancient carbon stocks. The decomposition of this remobilized carbon to CO2 or CH4 would in turn fuel further climate warming. Here we show that the glacial Zackenberg river in Northeastern Greenland likely exports a mixture of aged soil organic matter, recent bacteria and ice algae biomass residues, and deposited organic aerosols. In contrast, many of the smaller, nonglacial streams in the study area carried significantly older carbon from deeper soil layers or sedimentary rocks. More intense rainfall will likely increase these carbon fluxes. However, close interactions of organic matter with mineral surfaces may hamper greenhouse gas production and instead promote burial in marine sediments. Therefore, the impact on atmospheric CO2 and climate may be limited.
Key Points
Particulate organic carbon (POC) carried by glacial Zackenberg river shows uniform composition despite diverse inputs from tributaries
Geology and hydrologic conditions control POC composition in small periglacial streams with rain events eroding more ancient carbon
Organic matter in soils and river sediments throughout Zackenberg valley is largely associated with minerals