Early Eocene subarctic terrestrial paleoclimatology inferred from stable hydrogen isotope ratios of precipitation using mummified wood

使用木乃伊木乃伊从降水稳定氢同位素比推断早始新世亚北极陆地古气候学

• 批准号: 420409273
• 负责人: Dr. Tobias Anhäuser
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/420409273?language=en
• 关键词: Early; Eocene; subarctic; terrestrial; paleoclimatology

The early Eocene (~55-50 million years before present [Ma]) was characterized by a 'hothouse' climate as a result of high atmospheric greenhouse gas concentrations. This interval is regarded as analogue for near-future climatic conditions and has therefore been subject of intense (paleo-) climate studies. However, most of Eocene climate dynamics is reconstructed using marine climate archives whereby the terrestrial realm is less understood due to a lack of appropriate archives. Helpful for terrestrial climate investigations may be the use of mummified (non-petrified) wood found in Eocene volcaniclastic kimberlites. Depending on the state of preservation climate proxies such as tree-ring width and compound-specific stable hydrogen isotope ratios (expressed as Delta 2H values) at annual resolution can be determined. The University of Toronto (Canada) holds a large mummified wood collection (supervised by Prof. Jochen Halfar) comprising 12 multi-decadal to -centennial length tree-ring series at annual to pentadal resolution. Specimens were found in three early Eocene kimberlites such as Diavik A-154 (55.5 Ma), Diavik A-418 (55.2 Ma) and Ekati Panda (53.3 Ma) in the subarctic Northwest Territories (Canada). In a recent pioneer study (using three of the 12 mummified tree-ring series) I proposed the lignin methoxyl groups as promising climate proxy for mummified wood as (i) lignin is the dominant remaining wood compound largely excluding the extraction of commonly used cellulose and (ii) in modern trees their delta 2H values reflect the climate-sensitive delta 2H value in precipitation modulated by a uniform isotope fractionation (expressed as epsilon value). However, reconstructions of delta 2H in precipitation using the found ancient taxa (Taxodioxylon) are - at this early stage of research - hampered since the epsilon value of the nearest living relatives, Metasequoia glyptostroboides, has yet to be determined. Here, I propose to calibrate the species-specific epsilon value of Metasequoia glyptostroboides at a Canadian study site to strengthen the potential of delta 2H values of lignin methoxyl groups as a climate proxy. Subsequently, the calibrated epsilon value will be used to produce unprecedented high-resolution, multi-centennial length reconstructions of early Eocene terrestrial climate by exploiting the full mummified wood collection available at the University of Toronto. Hence, this research is not only expected to establish the delta 2H values of lignin methoxyl groups as 'proxy of choice' for mummified wood samples but also significantly advance knowledge of terrestrial paleoclimatology of the early Eocene, a climatically important period for the understanding of near-future climate conditions in a high-CO2 world.

始新世早期（距今约55-5000万年[Ma]）的特点是由于大气中温室气体浓度高而形成“温室”气候。该区间被视为近期气候条件的模拟，因此一直是深入（古）气候研究的主题。然而，大多数始新世气候动态都是利用海洋气候档案重建的，而由于缺乏适当的档案，对陆地领域的了解较少。使用在始新世火山碎屑金伯利岩中发现的木乃伊（非石化）木材可能有助于陆地气候调查。根据保存状态，可以确定年分辨率的气候指标，例如树木年轮宽度和特定化合物的稳定氢同位素比率（表示为 Delta 2H 值）。多伦多大学（加拿大）拥有大量木乃伊收藏（由 Jochen Halfar 教授监督），其中包括 12 个数十年至百年长度的树木年轮系列，分辨率为每年至五周年。在亚北极西北地区（加拿大）的三个早始新世金伯利岩中发现了样本，例如 Diavik A-154（55.5 Ma）、Diavik A-418（55.2 Ma）和 Ekati Panda（53.3 Ma）。在最近的一项先驱研究中（使用 12 个木乃伊年轮系列中的三个），我提出木质素甲氧基团作为木乃伊木材有前途的气候代表，因为 (i) 木质素是主要的剩余木材化合物，很大程度上不包括常用纤维素的提取和(ii) 在现代树木中，它们的 delta 2H 值反映了由均匀同位素分馏（表示为 epsilon 值）调节的降水中气候敏感的 delta 2H 值。然而，在研究的早期阶段，使用发现的古代分类单元（Taxodioxylon）重建降水中的 delta 2H 受到阻碍，因为最近的现存亲戚水杉的 epsilon 值尚未确定。在这里，我建议在加拿大的一个研究地点校准水杉的物种特异性 epsilon 值，以增强木质素甲氧基团的 delta 2H 值作为气候代理的潜力。随后，通过利用多伦多大学现有的完整木乃伊木材收藏，校准后的 epsilon 值将用于对始新世早期陆地气候进行前所未有的高分辨率、数百年长度的重建。因此，这项研究不仅有望确立木质素甲氧基团的 δ2H 值作为木乃伊木材样品的“选择代理”，而且还能显着增进对始新世早期陆地古气候学的了解，这是了解近来气候的重要时期。 -高二氧化碳世界的未来气候条件。