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 800 000 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 ∼100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At ∼134 000 and ∼129 000 years before present (hereafter ka), both CH4 and N2O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard–Oeschger events identified in the last glacial period. In addition, gradually rising N2O levels at ∼130 ka resemble a pattern of increasing N2O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH4 and N2O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed.

Precisely constrained 134-ka strong monsoon event in the penultimate deglaciation by an annually laminated speleothem from the Asian monsoon domain

“…The 134-ka event is a strong ASM interval centered at 134.5 ka in the penultimate deglaciation, characterized by a significantly negative oxygen isotope (δ 18 O) excursion in the speleothem records from the ASM domain (e.g., Cheng et al, 2006;Kelly et al, 2006;Wang et al, 2018;Duan et al, 2019). Atmospheric methane (CH 4 ) and nitrous oxide (N 2 O) also show significant peaks at approximately 134 ka, as recorded in the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) ice core records (Schmidely et al, 2021). The rise in CH 4 concomitant with the event also can be seen in the Vostok ice core record (Delmotte et al, 2004), and presumably resulted from the expanded wetland due to enhanced tropical rainfall and temperature in NH (Bock et al, 2017).…”

The ST22 chronology for the Skytrain Ice Rise ice core – part 2: an age model to the last interglacial and disturbed deep stratigraphy

“…Ten discrete samples were therefore measured at the University of Bern between 533-546 m, and a further 25 samples between 600 and 650 m depth. Details of the method have been published elsewhere (Schmidely et al, 2021). Concentrations ranged between 413 and 644 ppb, with an estimated precision (1 sigma) of 7 ppb (Table S1).…”

“…Concentrations ranged between 413 and 644 ppb, with an estimated precision (1 sigma) of 7 ppb (Table S1). Note that the discrete data presented here have been corrected by -18 ppb (Schmidely et al, 2021) to align them with previously published CH4 records. These offsets are potentially due to different remnant solubility of CH4 in meltwater using different melt extraction methods in different labs.…”

“…These offsets are potentially due to different remnant solubility of CH4 in meltwater using different melt extraction methods in different labs. Taking the uncertainty of the correction into account, the total uncertainty is estimated at 12 ppb (Schmidely et al, 2021), while that of the reference data is estimated at 10 ppb (Loulergue et al, 2008). Combining these uncertainties suggests that when comparing absolute values of methane (discrete data) with reference datasets we should allow an uncertainty of 16 ppb (much higher offsets are possible for the data derived by CFA, and there we mainly look for similar patterns to those in the reference data).…”

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

“…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 cm. 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).…”