The Palaeocene/Eocene thermal maximum, ∼55 million years ago, was a brief period of widespread, extreme climatic warming1,2,3, that was associated with massive atmospheric greenhouse gas input4. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition5. We show that sea surface temperatures near the North Pole increased from ∼18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations6, but the absolute polar temperatures that we derive before, during and after the event are more than 10 °C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds7 or hurricane-induced ocean mixing8—to amplify early Palaeogene polar temperatures.
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A.S. thanks the Utrecht Biogeology Centre for funding. H.B. thanks the Netherlands Organization for Scientific Research, and Utrecht University for enabling participation in the ACEX expedition. M.H. thanks the Purdue Climate Change Research Center, ITaP and the Purdue Research Foundation for their continued support. This research used samples and data provided by the IODP. We thank L. Bik, J. van Tongeren, N. Welters and A. van Dijk for technical support, and C. E. Stickley for discussions. Author Contributions A.S. and H.B. carried out the palynology, A.S. & G.-J.R. the δ13CTOC, S.S., M.W. and J.S.S.D. the TEX86′, BIT and isorenieratane analyses. R.S. generated the hydrogen index data. J.B. and K.M. were the co-chiefs of the ACEX expedition. N.P., J.M and the Expedition 302 Scientists were involved in generating shipboard and shore-based ACEX data. A.S., S.S., M.P., H.B., J.S.S.D., G.R.D., M.H. and L.J.L. contributed to interpreting the data and writing the paper.
This file contains Supplementary Methods, Supplementary Discussion, Supplementary Figures 1–3, Supplementary Table 1 and additional references.