Increasing Organic Carbon Biolability With Depth in Yedoma Permafrost: Ramifications for Future Climate Change

Abstract

Permafrost thaw subjects previously frozen organic carbon (OC) to microbial decomposition, generating the greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4) and fueling a positive climate feedback. Over one quarter of permafrost OC is stored in deep, ice‐rich Pleistocene‐aged yedoma permafrost deposits. We used a combination of anaerobic incubations, microbial sequencing, and ultrahigh‐resolution mass spectrometry to show yedoma OC biolability increases with depth along a 12‐m yedoma profile. In incubations at 3 °C and 13 °C, GHG production per unit OC at 12‐ versus 1.3‐m depth was 4.6 and 20.5 times greater, respectively. Bacterial diversity decreased with depth and we detected methanogens at all our sampled depths, suggesting that in situ microbial communities are equipped to metabolize thawed OC into CH4. We concurrently observed an increase in the relative abundance of reduced, saturated OC compounds, which corresponded to high proportions of C mineralization and positively correlated with anaerobic GHG production potentials and higher proportions of OC being mineralized as CH4. Taking into account the higher global warming potential (GWP) of CH4 compared to CO2, thawed yedoma sediments in our study had 2 times higher GWP at 12‐ versus 9.0‐m depth at 3 °C and 15 times higher GWP at 13 °C. Considering that yedoma is vulnerable to processes that thaw deep OC, our findings imply that it is important to account for this increasing GHG production and GWP with depth to better understand the disproportionate impact of yedoma on the magnitude of the permafrost carbon feedback.

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

“…While there are differences in study design, this may be due to the epigenetic formation of permafrost at our study site, and that a significant proportion of peat that accumulated prior to thaw is recalcitrant upon thawing as it has already undergone millennia of anaerobic decomposition (Beer et al, ; Zoltai, ). Areas where soil C accumulated syngenetically with permafrost have more labile C available to microbial decomposition and are more at risk of experiencing large loss of C post‐thaw (Heslop et al, ; Knoblauch et al, ; Strauss et al, ). We observed nonsignificant losses of C which were smaller than those reported from similar sites (Jones et al, ; O'Donnell et al, ), and we were unable to detect any significant increase to peat humification.…”

Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes

“…Both thawing and intact permafrost often contain relatively high concentrations of iron oxides, nitrate, or sulfate that can be reduced to respire organic carbon, thereby inhibiting methanogenesis. (Herndon et al, 2017;Heslop et al, 2019;Keuper et al, 2012;Winkel et al, 2019). Additionally, rates of methanogenesis have been shown to increase at higher temperatures (Yvon-Durocher et al, 2014).…”

Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

“…The organic matter incorporated into FLU and LAC has likely experienced Holocene decomposition since they were waterlogged during this period, whereas MOR likely been preserved since the Pleistocene and experienced very low decomposition (Strauss et al, 2017). During Holocene decomposition, labile OM, such as aliphatic and peptide-like compounds, in FLU and LAC deposits have been reworked by microbial activity, thereby leaving a higher amount of less labile compounds, such as aromatic compounds, when refrozen during the cooling of the middle Holocene (Stapel et al, 2017;Strauss et al, 2017;Heslop et al, 2019).…”