Predicting long‐term carbon mineralization and trace gas production from thawing permafrost of Northeast Siberia

Abstract

The currently observed Arctic warming will increase permafrost degradation followed by mineralization of formerly frozen organic matter to carbon dioxide (CO2 ) and methane (CH4 ). Despite increasing awareness of permafrost carbon vulnerability, the potential long-term formation of trace gases from thawing permafrost remains unclear. The objective of the current study is to quantify the potential long-term release of trace gases from permafrost organic matter. Therefore, Holocene and Pleistocene permafrost deposits were sampled in the Lena River Delta, Northeast Siberia. The sampled permafrost contained between 0.6% and 12.4% organic carbon. CO2 and CH4 production was measured for 1200 days in aerobic and anaerobic incubations at 4 °C. The derived fluxes were used to estimate parameters of a two pool carbon degradation model. Total CO2 production was similar in Holocene permafrost (1.3 ± 0.8 mg CO2 -C gdw(-1) aerobically, 0.25 ± 0.13 mg CO2 -C gdw(-1) anaerobically) as in 34 000-42 000-year-old Pleistocene permafrost (1.6 ± 1.2 mg CO2 -C gdw(-1) aerobically, 0.26 ± 0.10 mg CO2 -C gdw(-1) anaerobically). The main predictor for carbon mineralization was the content of organic matter. Anaerobic conditions strongly reduced carbon mineralization since only 25% of aerobically mineralized carbon was released as CO2 and CH4 in the absence of oxygen. CH4 production was low or absent in most of the Pleistocene permafrost and always started after a significant delay. After 1200 days on average 3.1% of initial carbon was mineralized to CO2 under aerobic conditions while without oxygen 0.55% were released as CO2 and 0.28% as CH4 . The calibrated carbon degradation model predicted cumulative CO2 production over a period of 100 years accounting for 15.1% (aerobic) and 1.8% (anaerobic) of initial organic carbon, which is significantly less than recent estimates. The multiyear time series from the incubation experiments helps to more reliably constrain projections of future trace gas fluxes from thawing permafrost landscapes.

Responses of peat carbon at different depths to simulated warming and oxidizing

“…With 15-30% of total world soil carbon, peatlands, mainly distribute in the northern high latitude areas, are an important carbon sink for the atmosphere (Gorham, 1991;Knoblauch et al, 2013;Lee et al, 2012). Large quantity of carbon deposits in peatlands is a result of the imbalance between production and decomposition (Knoblauch et al, 2013;Laiho, 2006).…”

“…Large quantity of carbon deposits in peatlands is a result of the imbalance between production and decomposition (Knoblauch et al, 2013;Laiho, 2006). The decomposition was much lower than production for water saturated condition in peatlands and the consequent anaerobic environment accompanied with low temperature (Bubier et al, 2003;Griffis et al, 2000).…”

“…Climate warming, land use changes and hydrologic redistribution have changed local, regional and global carbon cycle (Hicks Pries and Schuur, 2013) and have the potential to shift peatlands from a carbon sink to a carbon source (Dorrepaal et al, 2009;Knoblauch et al, 2013;Schuur et al, 2009;Wang et al, 2013;Yan et al, 2014). High altitude areas where climate is sensitive to warming are experiencing a "much larger than average" increase in temperature (Knoblauch et al, 2013;Lee et al, 2012;Liu and Chen, 2000;Peng et al, 2014). Besides warming, water table drawdown is the other very important cause for the degradation of peatlands in recent decades on Zoige Plateau peatlands -one of the largest alpine peatlands in the world (Bai et al, 2013;Chen et al, 2010;Gao, 2006;Li et al, 2010).…”

“…Water table drawdown may destroy the stable environment in peatlands, exposing the preserved carbon to aerobic (AE) environment (Oechel et al, 1998), and together with the optimum soil moisture creating an available environment for microbes (Serreze et al, 2000;Yan et al, 2014;Zimov et al, 2006). Water table drawdown also shifts soil respiration (Rs) pathway from anaerobic (AN) to aerobic environment, which responds to climate change differently (Knoblauch et al, 2013;Lee et al, 2012;Schuur et al, 2008;Treat et al, 2014;Yang et al, 2014). Studies showed that the stored old carbon in deep soil of degraded peatlands had participated in modern carbon cycle (McCallister and Del Giorgio, 2012;Schuur et al, 2009;Singer et al, 2012).…”

Cold carbon storage

“…The probability of a huge carbon release will depend not only on climate, but also on the degradability of alas carbon upon thaw: if we are unlucky, alas carbon degrades at similarly high rates to those reported for yedoma carbon 11 , but information about this is scarce 5,12 . We need to fill fundamental gaps in our understanding of the complex dynamics of the permafrost landscape if we are to predict the effects of climate change on such a huge carbon stock.…”