The environmental water of the middle Eocene Arctic:Evidence from δD, δ18O and δ13C within specific compounds

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Jahren, A. Hope, Byrne, Monica C., Graham, Heather V., Sternberg, Leonel S L, Summons, Roger E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2009
• Subjects: Arctic; Axel Heiberg Island; Heiberg; Polar Ice Cap
• Online Access: https://researchers.mq.edu.au/en/publications/d0d15737-56a2-48ab-9441-97d296246c93; https://doi.org/10.1016/j.palaeo.2008.09.016; http://www.scopus.com/inward/record.url?scp=57749199715&partnerID=8YFLogxK

The extensive vertical exposure (> 150 m) of terrestrial sediments on Axel Heiberg Island, which contain thick fossiliferous lignites, presents an exceptional opportunity to follow the establishment and re-establishment of Arctic Metasequoia forests during the middle Eocene. We compared δD values in n-alkanes of chain length 23, 25, 27 and 29 with δ 18 O values in phenylglucosazone (P-G) derived from α-cellulose; we also analyzed %-abundance of ferns, gymnosperms and angiosperms using pollen and spores isolated from each lignite. Our results showed that forest composition was altered upon uplift, as gymnosperms became more abundant within the relatively well-drained upland sediments. This was also reflected in the small (1‰), but significant, increase in the δ 13 C value of TOM from lowland to upland environments. However, neither the δD values of n-alkanes nor the δ 18 O in P-G were statistically different in the upland sediments, as compared to the lowland sediments; from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests. The δD value of environmental water implied by both n-alkanes and P-G ranged from - 168 to - 131% and was considerably enriched compared to all environmental water samples available from the modern Arctic region (< - 180%). In addition to indicating a warmer Eocene Arctic, subject to meteoric transport patterns different from today's, these results argue against the presence of an Eocene polar ice cap.