Atmospheric methane variability through the Last Glacial Maximum and deglaciation mainly controlled by tropical sources

Riddell-Young, Ben; Rosen, Julia; Brook, Edward; Buizert, Christo; Martin, Kaden; Lee, James; Edwards, Jon; Mühl, Michaela; Schmitt, Jochen; Fischer, Hubertus; Blunier, Thomas (2023). Atmospheric methane variability through the Last Glacial Maximum and deglaciation mainly controlled by tropical sources. Nature geoscience, 16(12), pp. 1174-1180. Springer Nature 10.1038/s41561-023-01332-x

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Constraining the causes of past atmospheric methane variability is
important for understanding links between methane and climate. Abrupt
methane changes during the last deglaciation have been intensely studied
for this purpose, but the relative importance of high-latitude and tropical
sources remains poorly constrained. The methane interpolar concentration
difference reflects past geographic emission variability, but existing records
suffered from subtle but considerable methane production during analysis.
Here, we report an ice-core-derived interpolar difference record covering
the Last Glacial Maximum and deglaciation, with substantially improved
temporal resolution, chronology and a critical correction for methane
production in samples from Greenland. Using box models to infer latitudinal
source changes, we show that tropical sources dominated abrupt methane
variability of the deglaciation, highlighting their sensitivity to abrupt
climate change and rapidly shifting tropical rainfall patterns. Northern
extratropical emissions began increasing ~16,000 years ago, probably
through wetland expansion and/or permafrost degradation induced by
high-latitude warming, and contributed at most 25 Tg yr−1 (45% of the total
emission increase) to the abrupt methane rise that coincided with rapid
northern warming at the onset of the Bølling–Allerød interval. These
constraints on deglacial climate–methane cycle interactions can improve
the understanding of possible present and future feedbacks.

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