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Episodic fresh surface waters in the Eocene Arctic Ocean

Abstract

It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions1 that characterized the early Palaeogene period (55–45 Myr ago) probably induced an intensified hydrological cycle2 with precipitation exceeding evaporation at high latitudes3. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an 800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas4,5,6,7 probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea8. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from 10 °C to 13 °C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas.

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Figure 1: The early Eocene Arctic basin, site locations, and geographic distribution of the Azolla pulse in adjacent basins.
Figure 2: Core recovery, chronology, palynological, physical properties and geochemical data across the Azolla phase of holes 302-4A and 913B.
Figure 3: Azolla mega- and microspores from Hole 302-4A-11X.

References

  1. Zachos, J. C., Pagani, M., Sloan, L. C., Thomas, E. & Billups, K. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292, 686–693 (2001)

    ADS  CAS  Article  Google Scholar 

  2. Barron, E. J., Hay, W. W. & Thompson, S. The hydrologic cycle: A major variable during Earth history. Glob. Planet. Change 1, 157–174 (1989)

    ADS  Article  Google Scholar 

  3. Huber, M., Sloan, L. C. & Shellito, C. J. in Causes and Consequences of Globally Warm Climates in the Early Palaeogene (eds Wing, S. L., Gingerich, P. D., Schmitz, B. & Thomas, E.) 25–47 (GSA Special Paper 369, Geological Society of America, Boulder, Colorado, 2003)

    Google Scholar 

  4. Boulter, M. C. Pollen and spore events from the marine Tertiary of North Europe. J. Micropalaeontol. 5, 75–84 (1986)

    Article  Google Scholar 

  5. Bujak, J. P. & Mudge, D. C. A high-resolution North Sea Eocene dinocyst zonation. J. Geol. Soc. Lond. 151, 449–462 (1994)

    Article  Google Scholar 

  6. Eldrett, J. S., Harding, I. C., Firth, J. V. & Roberts, A. P. Magnetostratigraphic calibration of Eocene-Oligocene dinoflagellate cyst biostratigraphy from the Norwegian-Greenland Sea. Mar. Geol. 204, 91–127 (2004)

    ADS  Article  Google Scholar 

  7. Gradstein, F. M. & Agterberg, F. in Quantitative Stratigraphic Correlation (eds Cubitt, J. M. & Reyment, R. A.) 119–175 (Wiley & Sons, Chichester, UK, 1982)

    Google Scholar 

  8. Heilmann-Clausen, C. in Early Paleogene Stage Boundaries. Abstracts and Field Trip Guides (ed. Molina, E.) 19 (University of Zaragoza, Zaragoza, Spain, 1996)

    Google Scholar 

  9. Backman, J., Moran, K., McInroy, D. B., Mayer, L. A. & the Expedition 302 Scientists. Proc. IODP 302 doi:10.2204/iodp.proc.302.2006 (Integrated Ocean Drilling Program Management International, Inc., Edinburgh, 2006).

  10. Moran, K. et al. The cenozoic palaeoenvironment of the Arctic Ocean. Nature doi:10.1038/nature04800 (this issue)

  11. Rai, V. & Rai, A. K. Growth behaviour of Azolla pinnata at various salinity levels and induction of high salt tolerance. Plant Soil 206, 79–84 (1998)

    CAS  Article  Google Scholar 

  12. Arora, A. & Singh, P. K. Comparison of biomass productivity and nitrogen fixing potential of Azolla SPP. Biomass Bioenergy 24, 175–178 (2003)

    CAS  Article  Google Scholar 

  13. Collinson, M. E. The ecology of Cainozoic ferns. Rev. Palaeobot. Palynol. 119, 51–68 (2002)

    Article  Google Scholar 

  14. Collinson, M. E. Cainozoic ferns and their distribution. Brittonia 53, 173–235 (2001)

    Article  Google Scholar 

  15. Collinson, M. E. Palaeofloristic assemblages and palaeoecology of the Lower Oligocene Bembridge Marls, Hamstead Ledge, Isle of Wight. Bot. J. Linn. Soc. 86, 177–225 (1983)

    Article  Google Scholar 

  16. Sweet, A. R. & Hills, L. V. Early Tertiary species of Azolla subg. Azolla sect Kremastospora from western and arctic Canada. Can. J. Bot. 54, 334–351 (1976)

    Article  Google Scholar 

  17. Hopmans, E. C. et al. A novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids. Earth Planet. Sci. Lett. 224, 107–116 (2004)

    ADS  CAS  Article  Google Scholar 

  18. Sluijs, A. et al. Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum. Nature doi:10.1038/nature04668 (this issue)

  19. Schouten, S., Hopmans, E. C., Schefuß, E. & Sinninghe Damsté, J. S. Distributional variations in marine crenarchaeotal membrane lipids: a new tool for reconstructing ancient sea water temperatures? Earth Planet. Sci. Lett. 204, 265–274 (2002)

    ADS  CAS  Article  Google Scholar 

  20. Wuchter, C., Schouten, S., Coolen, M. J. L. & Sinninghe Damsté, J. S. Temperature-dependent variation in the distribution of tetraether membrane lipids of marine Crenarchaeota: Implications for TEX86 paleothermometry. Paleoceanography 19, doi:10.1029/2004PA001041 (2004)

  21. Powers, L. A. et al. Crenarchaeotal membrane lipids in lake sediments: A new paleotemperature proxy for continental paleoclimate reconstruction? Geology 32, 613–616 (2004)

    ADS  CAS  Article  Google Scholar 

  22. Greenwood, D. R. & Wing, S. L. Eocene continental climates and latitudinal temperature gradients. Geology 23, 1044–1048 (1995)

    ADS  Article  Google Scholar 

  23. Markwick, P. J. Fossil crocodilians as indicators of Late Cretaceous and Cenozoic climates: Implications for using palaeontological data in reconstructing palaeoclimate. Palaeogeogr. Palaeoclimatol. Palaeoecol. 137, 205–271 (1998)

    Article  Google Scholar 

  24. Tripati, A., Zachos, J., Marincovich, L. Jr & Bice, K. Late Paleocene Arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios. Palaeogeogr. Palaeoclimatol. Palaeoecol. 170, 101–113 (2001)

    Article  Google Scholar 

  25. Jahren, A. H. & Sternberg, L. S. L. Humidity estimate for the middle Eocene Arctic rain forest. Geology 31, 463–466 (2003)

    ADS  Article  Google Scholar 

  26. Fricke, H. C. & Wing, S. L. Oxygen isotope and paleobotanical estimates of temperature and δ18O-latitude gradients over North America during the early Eocene. Am. J. Sci. 304, 612–635 (2004)

    ADS  Article  Google Scholar 

  27. Huber, M. & Nof, D. The ocean circulation in the southern hemisphere and its climatic impacts in the Eocene. Palaeogeogr. Palaeoclimatol. Palaeoecol. 231, 9–28 (2006)

    Article  Google Scholar 

  28. Sloan, L. C. & Rea, D. K. Atmospheric carbon dioxide and early Eocene climate: A general circulation modeling sensitivity study. Palaeogeogr. Palaeoclimatol. Palaeoecol. 119, 275–292 (1996)

    Article  Google Scholar 

  29. Pagani, M., Zachos, J. C., Freeman, K. H., Tipple, B. & Bohaty, S. Marked decline in atmospheric carbon dioxide concentrations during the Paleogene. Science 309, 600–603 (2005)

    ADS  CAS  Article  Google Scholar 

  30. Pearson, P. N. & Palmer, M. R. Atmospheric carbon dioxide concentrations over the past 60 million years. Nature 406, 695–699 (2000)

    ADS  CAS  Article  Google Scholar 

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Acknowledgements

H.B. thanks the Netherlands Organization for Scientific Research (NWO) and Utrecht University for enabling participation in the ACEX expedition. A.S. thanks the Utrecht Biogeology Centre for funding. M.H. thanks the Purdue Research Foundation for funding. This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). We thank L. Bik, T. Brain, S. Gibbons, P. Goggin, N. Holloway, J. van Tongeren, N. Welters and M. Woltering for technical support and L.J. Lourens, H. Nohr-Hansen, M. Pagani, C.E. Stickley, G.L. Williams and J.C. Zachos for discussions. Author Contributions H.B., A.S., F.S. and J.S.E. carried out the palynology, S.S. and J.S.S.D. the TEX86 and BIT analyses, M.E.C., J.v.d.B. and H.v.K.-v.C. the palaeobotany, J.O. and K.T. generated siliceous microfossil numbers, while R.S. generated the TOC data. M.H. carried out the comparison to climate models. J.B. and K.M. were co-chiefs on the ACEX. J.P.B. and H.B. compiled the unpublished industrial palynological records. All authors contributed to writing the paper.

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Brinkhuis, H., Schouten, S., Collinson, M. et al. Episodic fresh surface waters in the Eocene Arctic Ocean. Nature 441, 606–609 (2006). https://doi.org/10.1038/nature04692

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