Arctic Amplification of Global Warming Strengthened by Sunlight Oxidation of Permafrost Carbon to CO₂

Abstract

Once thawed, up to 15% of the ∼1,000Pg of organic carbon (C) in arctic permafrost soils may be oxidized to carbon dioxide (CO 2) by 2,100, amplifying climate change. However, predictions of this amplification strength ignore the oxidation of permafrost C to CO 2 in surface waters (photomineralization). We characterized the wavelength dependence of permafrost dissolved organic carbon (DOC) photomineralization and demonstrate that iron catalyzes photomineralization of old DOC (4,000-6,300 a BP) derived from soil lignin and tannin. Rates of CO 2 production from photomineralization of permafrost DOC are twofold higher than for modern DOC. Given that model predictions of future net loss of ecosystem C from thawing permafrost do not include the loss of CO 2 to the atmosphere from DOC photomineralization, current predictions of an average of 208 Pg C loss by 2,299 may be too low by~14%. Plain Language Summary The thawing of organic carbon stored in arctic permafrost soils, and its oxidation to carbon dioxide (a greenhouse gas), is predicted to be a major, positive feedback on global warming. However, current estimates of the magnitude of this feedback do not include the oxidation of permafrost soil organic carbon flushed to sunlit lakes and rivers. Here we show that ancient dissolved organic carbon (>4,000 years old) draining permafrost soils is readily oxidized to carbon dioxide by sunlight. As a consequence, current estimates of additional global warming from the permafrost carbon feedback are too low.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Research has continued to quantify the permafrost carbon feedback that involves release of greenhouse gases from thawing permafrost in the Arctic [ 1 ]. Experiments on the wavelength dependence of the photodegradation of dissolved organic carbon (DOC) in permafrost indicated that also UV-A radiation was most efficient [ 314 ]. Laboratory manipulations indicated that variability in the photodegradation may be attributable to iron catalysed photoreactions of old DOC derived from soil lignin and tannin in the melted permafrost.…”

“…Laboratory manipulations indicated that variability in the photodegradation may be attributable to iron catalysed photoreactions of old DOC derived from soil lignin and tannin in the melted permafrost. Rates of CO 2 photoproduction from permafrost DOC were twofold higher than for modern DOC [ 314 ]. Model predictions of future net loss of ecosystem carbon from thawing permafrost do not include the loss of CO 2 to the atmosphere from DOC photodegradation.…”

“…One of the major sources of DOM involves release by melting of the permafrost in the Arctic [ 167 , 314 , 317 , 318 ]. Current research on photodegradation by UV radiation of Arctic dissolved organic matter [ 318 ] shows that formation of CO 2 is accompanied by buildup of a pool of partially photooxidised DOM that likely plays a role in photo-facilitated microbial degradation [ 167 ].…”

Measurement of Atmospheric CO2 Column Concentrations Based on Open-Path TDLAS

“…The SNR of 880 was determined based on the ratio of the maximal amplitude of measured CO 2 absorbance to the 1-σ background noise. In addition, the integral absorbance (τ) was obtained to be 2.5 × 10 −2 , and CO 2 concentration was calculated to be 458.89 ppm, according to Equation (5). Therefore, the minimum detection limit was 0.52 ppm, which confirms that the system can be used to measure the atmospheric CO 2 concentration.…”

“…Anthropogenic emissions of greenhouse gases (GHGs) have a significant impact on global warming, and carbon dioxide (CO 2 ) and methane (CH 4 ) account for 66% and 16% of radiative forcing, respectively [ 1 , 2 , 3 ]. During the last decade (2009–2019), CO 2 concentrations increased at the fastest observed decadal rate of change (2.4 ppm/year), which is higher than that during of any previous decade since direct atmospheric concentration measurements began in 1958 [ 4 , 5 ]. Measurement of the atmospheric CO 2 column concentrations is valuable for understanding regional carbon emissions, sources, and sinks [ 6 , 7 , 8 , 9 , 10 , 11 ].…”