Department of Earth Science, University of California, Santa Barbara, CA 93106.
Institute of Geosciences, Kiel University, 24118 Kiel, Germany.
Proc Natl Acad Sci U S A. 2022 Aug 30;119(35):e2201871119. doi: 10.1073/pnas.2201871119. Epub 2022 Aug 22.
The stability of widespread methane hydrates in shallow subsurface sediments of the marine continental margins is sensitive to temperature increases experienced by upper intermediate waters. Destabilization of methane hydrates and ensuing release of methane would produce climatic feedbacks amplifying and accelerating global warming. Hence, improved assessment of ongoing intermediate water warming is crucially important, especially that resulting from a weakening of Atlantic meridional overturning circulation (AMOC). Our study provides an independent paleoclimatic perspective by reconstructing the thermal structure and imprint of methane oxidation throughout a water column of 1,300 m. We studied a sediment sequence from the eastern equatorial Atlantic (Gulf of Guinea), a region containing abundant shallow subsurface methane hydrates. We focused on the early part of the penultimate interglacial and present a hitherto undocumented and remarkably large intermediate water warming of 6.8 °C in response to a brief episode of meltwater-induced, modest AMOC weakening centered at 126,000 to 125,000 y ago. The warming of intermediate waters to 14 °C significantly exceeds the stability field of methane hydrates. In conjunction with this warming, our study reveals an anomalously low δC spike throughout the entire water column, recorded as primary signatures in single and pooled shells of multitaxa foraminifers. This extremely negative δC excursion was almost certainly the result of massive destabilization of methane hydrates. This study documents and connects a sequence of climatic events and climatic feedback processes associated with and triggered by the penultimate climate warming that can serve as a paleoanalog for modern ongoing warming.
广泛分布的海洋大陆边缘浅表层沉积物中甲烷水合物的稳定性对上层中层水经历的温度升高极为敏感。甲烷水合物的失稳以及随后释放的甲烷将产生气候反馈，放大并加速全球变暖。因此，改进对正在发生的中层水变暖的评估至关重要，尤其是由大西洋经向翻转环流（AMOC）减弱引起的变暖。我们的研究通过重建 1300 米水柱的热结构和甲烷氧化的印记，提供了一个独立的古气候视角。我们研究了东赤道大西洋（几内亚湾）的一个沉积物序列，该地区含有丰富的浅层浅表层甲烷水合物。我们专注于上一个间冰期的早期，并提出了一个迄今为止未被记录的、非常显著的中层水变暖 6.8°C 的记录，这是对大约 126000 到 125000 年前以融水诱导的、适度的 AMOC 减弱为中心的短暂事件的响应。中层水变暖到 14°C 显著超过了甲烷水合物的稳定范围。伴随着这种变暖，我们的研究揭示了整个水柱中异常低的 δC 峰值，这是在单细胞和多细胞有孔虫的组合壳中作为主要特征记录下来的。这种极其负的 δC 偏移几乎可以肯定是甲烷水合物大规模失稳的结果。本研究记录并连接了一系列与上一个间冰期变暖相关联的气候事件和气候反馈过程，并由其引发，可作为现代正在发生的变暖的古气候类比。
