CH<sub>4</sub> and N<sub>2</sub>O fluctuations during the penultimate deglaciation

Abstract

Abstract. Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 thousand years. Reconstructions of millennial to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of about ~ 100 years. Our data permit the identification of centennial-scale fluctuations standing out of the overall transition to interglacial levels. These features occurred in concert with reinvigorations of the Atlantic Meridional Overturning Circulation (AMOC) and northward shifts of the Intertropical Convergence Zone. The abrupt CH4 and N2O rises at about ~ 134 and ~ 128 thousand of years before present (hereafter ka BP) are assimilated to the fluctuations accompanying the Dansgaard–Oeschger events of the last glacial period, while rising N2O levels at ~ 130.5 ka BP are assimilated to a pattern of increasing N2O concentrations that characterized the end of Heinrich stadials. We suggest the 130.5-ka event to be driven by a partial reinvigoration of the AMOC. Overall, the CH4 and N2O fluctuations during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation. However, trace gas responses may differ for similar type of climatic events, as exemplified by the reduced amplitude and duration of the 134-ka event compared to the fluctuations of the Bølling–Allerød during the last deglaciation.

Laser-induced sublimation extraction for centimeter-resolution multi-species greenhouse gas analysis on ice cores

“…Generally, our EDC samples agree well with the published record, but there is a tendency to a positive bias of ∼ 7 ppb, even for interglacial samples not affected by in situ production. A similarly high bias compared to previous literature values has been observed recently by Schmidely et al (2021) using a refined, more efficient melt extraction technique and may point to non-quantitative extraction of highly soluble N 2 O from the meltwater in older studies. The 100 % extraction efficiency of our sublimation method avoids any such solubility issues.…”

“…Alternatively, CH 4 concentrations can be measured in continuous flow analysis (CFA) campaigns with typical depth resolution of 5-10 cm (Stowasser et al, 2012;Chappellaz et al, 2013;Rhodes et al, 2017). The discrete sample method requires a sample size of 20-40 g of ice (Schilt et al, 2010a;Mitchell et al, 2011;Baumgartner et al, 2014;Ryu et al, 2018;Schmidely et al, 2021), corresponding to a typical depth resolution of several centimeters. CH 4 records from melt extraction techniques of discrete ice samples can be affected by production of CH 4 during extraction (in extractu) observed in dusty glacial ice from Greenland (Lee et al, 2020;Muehl et al, 2022).…”

Review of “CH4 and N2O fluctuations during the penultimate deglaciation” by Schmidely et al. (2020)

“…: maybe give a one-sentence description of the IRMS setup for N2O istopes L91: acknowledge this is also the approach used by the Japanese lab at NIPR (Oyabu et al, 2020) Section 2: More details are needed here, as outlined above.…”