Plots showing probability distributions derived from measurements of 14C in long-chain fatty acids
Probability distributions derived from measurements of 14C in long-chain fatty acids (LCFAs) reported in the paper. Here, the 14C ages are subtracted from the independently determined depositional age of the sediment to give a ‘pre-depositional age’ of the carbon in these plant-wax derived C compounds. The two distributions (left panel) demonstrate that mean pre-depositional LCFA ages for sediments deposited after the end of the little ice age (red, Post 100 cal. y BP) averaged about 6140 years, indicating the age of C in these compounds in soil that eroded into the river, was transported and deposited at the river mouth. These are on average about 930 years (right panel) older than the same compounds deposited before the termination of the Little Ice Age (yellow, Pre 100 cal. y BP). This supports the idea that in colder periods, shallower thaw layer depths mean younger C is eroded and deposited at the river mouth in the Colville River basin, while in warm periods, deeper thaw layers mean older eroded C. Credit: Zhang et al. [2021], Figure 4
Source: AGU Advances

With amplified warming of the Arctic, there is increasing concern about thawing of permafrost and the fate of the large amounts of organic material it contains. Zhang et al. [2021] report a 2700-year record of variations in the radiocarbon age of carbon in bulk organic matter and plant waxes originating from a the Alaskan Colville river, a watershed underlain by continuous permafrost.

Pre-depositional ages for bulk C ranged from about 1000 to 4300 years, while isolated plant waxes were even older, indicating that erosion was the major contributor to deposited organic matter. During colder periods, pre-depositional ages of plant waxes were about 930 years younger than during warmer periods before and after, suggesting shallower depths of seasonal thaw in cooler periods, and deepening in warmer periods.  Over the past century, the age of deposited carbon has increased, providing evidence supporting increased thaw depths, and therefore also presumably C export, with current global warming.

Citation: Zhang, X., Bianchi, T., Hanna, A. et al. [2021]. Recent Warming Fuels Increased Organic Carbon Export from Arctic Permafrost. AGU Advances, 2, e2021AV000396.

—Susan Trumbore, Editor-in-Chief, AGU Advances

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