Carbon and hydrogen isotope fractionation under continuous light: implications for paleoenvironmental interpretations of the High Arctic during Paleogene warming
The effect of low intensity continuous light, e.g., in the High Arctic summer, on plant carbon and hydrogen isotope fractionations is unknown. We conducted greenhouse experiments to test the impact of light quantity and duration on both carbon and hydrogen isotope compositions of three deciduous conifers whose fossil counterparts were components of Paleogene Arctic floras: Metasequoia glyptostroboides, Taxodium distichum, and Larix laricina. We found that plant leaf bulk carbon isotopic values of the examined species were 1.75–4.63‰ more negative under continuous light (CL) than under diurnal light (DL). Hydrogen isotope values of leaf n-alkanes under continuous light conditions revealed a D-enriched hydrogen isotope composition of up to 40‰ higher than in diurnal light conditions. The isotope offsets between the two light regimes is explained by a higher ratio of intercellular to atmospheric CO2 concentration (C i/C a) and more water loss for plants under continuous light conditions during a 24-h transpiration cycle. Apparent hydrogen isotope fractionations between source water and individual lipids (εlipid–water) range from −62‰ (Metasequoia C27 and C29) to −87‰ (Larix C29) in leaves under continuous light. We applied these hydrogen fractionation factors to hydrogen isotope compositions of in situ n-alkanes from well-preserved Paleogene deciduous conifer fossils from the Arctic region to estimate the δD value in ancient precipitation. Precipitation in the summer growing season yielded a δD of −186‰ for late Paleocene, −157‰ for early middle Eocene, and −182‰ for late middle Eocene. We propose that high-latitude summer precipitation in this region was supplemented by moisture derived from regionally recycled transpiration of the polar forests that grew during the Paleogene warming.
KeywordsArctic Stable isotope Paleogene Paleoclimate Deciduous conifers
This project was funded in part by the CAS/SAFEA International Partnership Program for Creative Research Teams, the Pilot Project of Knowledge Innovation, CAS (KZCX2-YW-105), the Major Basic Research Projects (2006CB806400), the National Science Foundation of China (40402002 and 40872011), the American Chemical Society Petroleum Research Funds, and Bryant University Summer Research Fund. Most of the work presented in this paper was carried out during H.Y.’s sabbatical year at Yale University with M.P. and D.E.G.B. We thank Jingfeng Wang (MIT) for discussion of the recycling model, Liang Xiao (Bryant University) for preparation of diagrams, and Gerard Olack (Yale University) for technical supports. This paper is the contribution 200901 for the Laboratory of Terrestrial Environment of Bryant University. We declare that the experiments comply with the current laws of the United States in which the study was performed.
- Christie RL (1988) Field studies of “fossil forest” sites in the Arctic Islands. Geol Surv Can Pap 88-1D:57–60Google Scholar
- Eberle J, Storer JE (1999) Northernmost record of brontotheres, Axel Heiberg Island, Canada-implications for age of the Buchanan Lake Formation and brontothere paleobiology. J Paleontol 73:979–983Google Scholar
- Irving E, Wynne PJ (1991) The paleolatitude of the Eocene fossil forests of Arctic Canada. Geol Surv Can Bull 403:209–211Google Scholar
- LePage BA, Basinger JF (1991) Early Tertiary Larix from the Buchanan Lake Formation, Canadian Arctic Archipelago, and a consideration of the phytogeography of the genus. Geol Surv Can Bull 403:67–82Google Scholar
- Ögren E, Sundin U (1996) Photosynthetic responses to variable light: a comparison of species from contrasting habitats. Oecologia 106:18–27Google Scholar
- Osborne CP, Royer DL, Beerling DJ (2004) Adaptive role of leaf habit in extinct polar forests. Int For Rev 6:181–186Google Scholar
- Ricketts BD, McIntyre DJ (1986) The Eureka Sound Group of eastern Axel Heiberg Island: new data on the Eurekan Orogeny. Geol Surv Can Pap 86-1B:405–410Google Scholar
- Ricketts BD, Stephenson RA (1994) The demise of Sverdrup Basin: late Cretaceous–Paleogene sequence stratigraphy and forward modeling. J Sediment Res B64:516–530Google Scholar
- Yang H, Jin J-H (2000) Phytogeographic history and evolutionary stasis of Metasequoia: geological and genetic information contrasted. Acta Palaeontol Sin 39(suppl):288–307Google Scholar