Interactions of iron and organic matter as controls on the fate of permafrost carbon in the Arctic
EMSL Project ID
49345
Abstract
The ongoing thawing of permafrost soils is the only environmental change that allows tremendous stores of organic carbon (C) to be converted into carbon dioxide (CO2) on relatively short time scales, thus providing a positive and accelerating feedback to global warming. The fate of this soil C is first conversion to dissolved organic matter (DOM), and then oxidation to CO2. Our recent findings show that (1) photochemical reactions dominate the degradation of soil DOM exported to surface waters, (2) permafrost DOM is more susceptible to photo-degradation than expected based only on its chemical composition, and (3) abiotic, redox reactions involving iron and DOM in soils may initiate the oxidation of DOM to CO2. Our objective is to relate these three novel findings within a conceptual model where interactions between iron and DOM (i.e., complexation of iron by ligands within DOM) play a pivotal role in the conversion of DOM to CO2 in sunlit surface waters and dark soils. We propose that in sunlit surface waters, complexation of ferric iron likely enhances the photochemical oxidation of DOM to CO2. In contrast, in dark soils redox reactions of free (un-complexed) ferrous iron initiate oxidation of DOM to CO2. The complexation of iron by DOM in surface waters and soils remains too poorly understood to predict how iron may influence the oxidation of DOM to CO2, because there has been no analytical technique that can directly characterize the nature of iron-DOM complexes. The Environmental Science Molecular Laboratory (EMSL) has developed a novel technique that will allow us to fill knowledge gaps on the role of Fe-DOM complexation in oxidation of DOM to CO2. By combining advances in ultra-high resolution mass spectrometry (FT-ICR MS) with quantification of iron by LC-ICP-MS, it is now possible to resolve the specific compounds within DOM that associate with iron. Our aim is to use this pioneering technique to test hypotheses on the role of iron-DOM complexes in C degradation across environmental gradients representing common arctic landscapes. These analyses will be integrated with our ongoing chemical characterization of DOM and its susceptibility to conversion to CO2. Providing a mechanistic understanding of the controls on soil DOM degradation 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
2016-10-01
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members