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

• Applicant: Dr. Tobias Anhäuser
• Subject Area: Palaeontology
• Term: from 2019 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 420409273

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.

• DFG Programme: Research Fellowships
• International Connection: Canada
• Host: Professor Dr. Jochen Halfar