The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change. © 2006 Nature Publishing Group

Introduction The behavior and inf luence of the A rct ic Oceanthroughout the course of the global Cenozoic climateevolution have been virtually unknown. Only the uppermostfew meters of the Arctic’s sediment record, representingHolocene and late Pleistocene times, have been retrievedfrom ridges through a limited number of short piston,gravity, and box cores. Even less of the thick sedimentsequences, ~6 km in the Canada Basin and ~3 km in theNansen Basin(Grantz et al., 1990; Jokat et al., 1995), restingon the Arctic Ocean’s abyssal plains, have been cored.Prior to the Arctic Coring Expedition (ACEX), informationon Neogene or Paleogene conditions in the central Arcticwas limited to a 1.6-m interval in a 3.6-m-long T-3 gravitycore raised from the Alpha Ridge (Clark, 1974), providingthe sole evidence for marine conditions no older than themiddle Eocene in the central Arctic (Bukry, 1984)

The naturea nda ge ofthe Cenozoic compressional/transpressionaldeformation withint he NE Faroe-ShetlandB asin,the Wyville-Thomson Ridge andH atton Bankareashaveb eeninvestigated, primarily usingseismic reflection data.Inall three areas,the foldsreach approximately 2to4kminamplitude and40kmin wavelength.Early andmid-Eocenec ompressional/transpressionaldeformation affected the Hatton Banka nd Wyville-Thomson Ridge areas,andfoldingwaslocally activeevenearlier,duringPaleocene/Cretaceous times. However,the mainCenozoic compressional/transpressionalt ectonism thataffected the Hatton Banka rea was coevalw ithd evelopment ofthe regionalLateE oceneU nconformity (C30),a ndwithc hangesins preading geometriesandaphaseofaccelerated subsidence inthe Rockall Basin. Withinthe NE Atlantic margin,WNWto NW-trendinglineaments/transferz onesanda ssociated oceanic fracturezonesfacilitatesignificant structural segmentation. Offsets int he continent-oceanboundary alongH atton Bankprobably reflectinherited basin architecture, andmany Cenozoic foldsint he Hatton Bank, Wyville-Thomson Ridge andN EF aroe-Shetland Basinareasareconsidered to mainly reflectcompressionalbuttressingagainst pre-existingstructures. However, relatively small lateraldisplacements probably occurred alongsomereactivated transferz onesfollowing continentalbreak-up. Paleocene-Eocenecompressional/transpressionaldeformation mayhaveaffected parts of the Faroe-ShetlandB asin,b ut seismic resolution ofthisisl argely masked byp ervasivepolygonalfaulting. Significant,e arlyt om id-Miocenec ompressional/transpressionaldeformation isr ecordedi nt he NE Faroe-ShetlandB asin,a ndmayalso havee xerted amajor influence on the Wyville-Thomson Ridge and surroundingarea.Inparticular,mid-Miocenegrowthofthe FaroeBankChannelsynclinemayhaveresulted in major changesinn orthern hemisphered eep-oceancirculation witha ssociated impacto nglobalclimate.Compressional/transpressionaldeformation appears to havecontinued into Pliocene-?Recent timesandresulted int he development offeaturessuch asthe Pilot WhaleAnticlineanda ssociated mudvolcanoes/diapirs.

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Core Curator † /Curatorial Specialist Bremen Core Repository (BCR) †Participated in shipboard operations.