The fate of newly exposed carbon in the Arctic - controls on release to the atmosphere and transport to the ocean
EMSL Project ID
48360
Abstract
The carbon (C) in thawing permafrost soils may have global impacts on climate change, yet the controls on processing and fate of this newly released C are poorly understood. Inland waters are important conduits of C from land to the atmosphere and ocean, and the fate of dissolved organic carbon (DOC) released from soils is either complete oxidation to CO2 or partial oxidation and river export to oceans. Our recent findings show that (1) photochemical reactions dominate the degradation of soil DOC exported to surface waters, (2) the fate of DOC varied consistently by location on the landscape, and (3) permafrost soils have distinct chemical signatures and photo-reactivity compared to currently thawed organic mats. Our objective is to relate these three novel findings within a conceptual model where DOC fate is controlled by initial DOC chemical composition and its history of light exposure. In this model, DOC from soil feeding headwater streams has low light history, and photo-reactions favor complete oxidation to CO2, whereas in lakes and large rivers prior light exposure is high and partial photo-oxidation is favored. To achieve our objective we will use ultra-high resolution and molecular characterization of DOC molecules concurrent with field degradation experiments to obtain a predictive understanding of the relationship between DOC chemistry, light exposure, and the pathways and magnitudes of DOC fate. We propose to use the high resolution mass spectrometry and NMR capabilities at EMSL which will provide a semi-quantitative assessment of the molecular composition of DOC in surface waters and thawed and permafrost soils. Comparing this composition to the light history and degradation rates measured experimentally in the field, we can determine the fate of DOC as CO2 emitted to the atmosphere or partially oxidized DOC transported downstream. EMSL has the combination of instruments and expertise with environmental soil water samples that allow both high molecular resolution and high sample throughput. High resolution mass spectrometry provides the unique molecular formulas for components within the DOC assemblage, and solid state 13C-NMR will be used to evaluate shifts in major functional group distributions on a subset of isolated DOC samples (previously collected). Samples will be analyzed across a gradient of geochemical factors that represent arctic landscapes and most likely influence the chemical composition and reactivity of soil carbon. By combining these techniques we can uniquely relate DOC source chemistry to photo-reactivity, and then track the degradation of DOC as it moves through surface waters by measuring the relative production of CO2 and partially oxidized DOC in controlled experiments. Providing a mechanistic understanding of the controls on soil DOC degradation across the landscape in the Arctic is needed to create the next generation of models that can better predict the impact of a thawing permafrost on global warming.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-10-01
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Ward C P,Cory R M 2015. "Chemical Composition of Dissolved Organic Matter Draining Permafrost Soils" Geochimica et Cosmochimica Acta 167():63-79. 10.1016/j.gca.2015.07.001
Ward C P,Cory R M 2016. "Complete and Partial Photo-oxidation of Dissolved Organic Matter Draining Permafrost Soils" Environmental Science & Technology 50(7):3545–3553. 10.1021/acs.est.5b05354