In:
Climate of the Past, Copernicus GmbH, Vol. 19, No. 5 ( 2023-05-22), p. 999-1025
Abstract:
Abstract. Air trapped in polar ice provides unique records of the past
atmospheric composition ranging from key greenhouse gases such as methane
(CH4) to short-lived trace gases like ethane (C2H6) and
propane (C3H8). Recently, the comparison of CH4 records
obtained using different extraction methods revealed disagreements in the
CH4 concentration for the last glacial in Greenland ice. Elevated
methane levels were detected in dust-rich ice core sections measured
discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH4 excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14:2:1, indicating a shared origin. The measured carbon isotopic signature of excess methane is (-47.0±2.9) ‰ and its deuterium isotopic signature is (-326±57) ‰. With the co-production ratios of excess alkanes
and the isotopic composition of excess methane we established a fingerprint
that allows us to constrain potential formation processes. This fingerprint
is not in line with a microbial origin. Moreover, an adsorption–desorption
process of thermogenic gas on dust particles transported to Greenland
does not appear very likely. Instead, the alkane pattern appears to be
indicative of abiotic decomposition of organic matter as found in soils and
plant leaves.
Type of Medium:
Online Resource
ISSN:
1814-9332
DOI:
10.5194/cp-19-999-2023
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2217985-9
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