Old carbon reservoirs were not important in the deglacial methane budget

Abstract

Permafrost and methane hydrates are large, climate-sensitive old carbon reservoirs that have the potential to emit large quantities of methane, a potent greenhouse gas, as the Earth continues to warm. We present ice core isotopic measurements of methane (Δ14C, δ13C, and δD) from the last deglaciation, which is a partial analog for modern warming. Our results show that methane emissions from old carbon reservoirs in response to deglacial warming were small (<19 teragrams of methane per year, 95% confidence interval) and argue against similar methane emissions in response to future warming. Our results also indicate that methane emissions from biomass burning in the pre-Industrial Holocene were 22 to 56 teragrams of methane per year (95% confidence interval), which is comparable to today.

East Siberian Arctic inland waters emit mostly contemporary carbon

“…Radiocarbon ( 14 C) based studies in Yedoma regions have shown that pre-aged C is highly vulnerable to microbial decomposition to CO 2 when released into streams [12][13][14] , while studies targeting thermokarst lakes (formed from abrupt thaw processes) detected CH 4 emissions as old as 42,900 years before present (yBP) 15 . In contrast, contemporary C dominated emissions to the atmosphere in non-Yedoma permafrost regions 6,7,16,17 , and ice-core studies suggest it is unlikely that large-scale emissions of pre-aged CH 4 from permafrost regions have occurred in the past~15,000 years 18 . It therefore remains unclear whether the release of preaged permafrost C into inland waters is an important driver of landscape-scale C emissions relative to contemporary C turnover.…”

Impact of tides and sea-level on deep-sea Arctic methane emissions

“…However, there is no consensus on how gas emissions from these dynamic systems fit into a climate-change scenario 20 . For example, while field observations on formerly glaciated margins point towards massive emissions of greenhouse gases following ice-sheet retreat 21 , recent analysis of ice-cores suggest that post-LGM (Last Glacial Maximum, ∼20,000 years ago) methane release from old reservoirs was too small to impact the global climate 22 . A challenging aspect on the quantification of present-day emissions is that seepage may be more widespread and abundant than we are able to identify based on the presence of gas plumes in hydro-acoustic surveys.…”

Extracting a History of Global Fire Emissions for the Past Millennium From Ice Core Records of Acetylene, Ethane, and Methane

“…Geologic ethane emissions in the modern atmosphere are estimated at 2–4 Tg year −1 (Etiope & Ciccioli, 2009). However, the importance and magnitude of geologic hydrocarbons in the preindustrial atmosphere has been heavily debated based on measurements of radiocarbon‐free methane in ice cores (Dyonisius et al, 2020; Hmiel et al, 2020; Petrenko et al, 2017).…”

“…Acetylene has a simple biogeochemical cycle, with fire as the major source during the preindustrial (see section 2.1 for global budget discussions) (Nicewonger et al, 2020; Xiao et al, 2007). Ethane has one additional source from geologic emissions, the magnitude of which is controversial (Dyonisius et al, 2020; Etiope & Ciccioli, 2009; Hmiel et al, 2020; Petrenko et al, 2017). Methane and CO are considerably more complex.…”

“…Methane and CO are considerably more complex. Microbial sources comprise most of the preindustrial CH 4 emissions with geologic emissions as another possible, but debated source (Dyonisius et al, 2020; Etiope & Ciccioli, 2009; Hmiel et al, 2020; Petrenko et al, 2017). CO has preindustrial sources from biomass burning and from atmospheric oxidation of methane and nonmethane hydrocarbons.…”