Riddell-Young Ben, Lee James Edward, Brook Edward J, Schmitt Jochen, Fischer Hubertus, Bauska Thomas K, Menking James A, Iseli René, Clark Justin Reid
College of Earth, Ocean, and Atmospheric Sciences (CEOAS), Oregon State University, Corvallis, OR, USA.
Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA.
Nature. 2025 Jan;637(8044):91-96. doi: 10.1038/s41586-024-08363-3. Epub 2025 Jan 1.
Understanding the causes of past atmospheric methane (CH) variability is important for characterizing the relationship between CH, global climate and terrestrial biogeochemical cycling. Ice core records of atmospheric CH contain rapid variations linked to abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (DO) events and Heinrich events (HE). The drivers of these CH variations remain unknown but can be constrained with ice core measurements of the stable isotopic composition of atmospheric CH, which is sensitive to the strength of different isotopically distinguishable emission categories (microbial, pyrogenic and geologic). Here we present multi-decadal-scale measurements of δC-CH and δD-CH from the WAIS Divide and Talos Dome ice cores and identify abrupt 1‰ enrichments in δC-CH synchronous with HE CH pulses and 0.5‰ δC-CH enrichments synchronous with DO CH increases. δD-CH varied little across the abrupt CH changes. Using box models to interpret these isotopic shifts and assuming a constant δC-CH of microbial emissions, we propose that abrupt shifts in tropical rainfall associated with HEs and DO events enhanced C-enriched pyrogenic CH emissions, and by extension global wildfire extent, by 90-150%. Carbon cycle box modelling experiments suggest that the resulting released terrestrial carbon could have caused from one-third to all of the abrupt CO increases associated with HEs. These findings suggest that fire regimes and the terrestrial carbon cycle varied contemporaneously and substantially with past abrupt climate changes of the last glacial period.
了解过去大气甲烷（CH₄）变化的原因对于描述CH₄、全球气候和陆地生物地球化学循环之间的关系至关重要。大气CH₄的冰芯记录包含与末次冰期的突然气候变化相关的快速变化，这些气候变化被称为丹斯加德-奥舍格（DO）事件和 Heinrich 事件（HE）。这些CH₄变化的驱动因素仍然未知，但可以通过对大气CH₄稳定同位素组成的冰芯测量来加以限制，大气CH₄稳定同位素组成对不同同位素可区分排放类别（微生物、热解和地质）的强度敏感。在这里，我们展示了来自WAIS Divide和Talos Dome冰芯的δ¹³C-CH₄和δD-CH₄的数十年尺度测量结果，并确定了与HE CH₄脉冲同步的δ¹³C-CH₄突然富集1‰，以及与DO CH₄增加同步的δ¹³C-CH₄富集0.5‰。在CH₄的突然变化中，δD-CH₄变化很小。使用箱式模型来解释这些同位素变化，并假设微生物排放的δ¹³C-CH₄恒定，我们提出与HEs和DO事件相关的热带降雨突然变化增强了富含¹³C的热解CH₄排放，进而使全球野火范围扩大了90-150%。碳循环箱式模型实验表明，由此释放的陆地碳可能导致了与HEs相关的突然CO₂增加的三分之一至全部。这些发现表明，火灾状况和陆地碳循环与末次冰期过去的突然气候变化同时发生且有很大变化。
