Using the concept of “orbital tuning”, a continuous, high-resolution deep-sea chronostratigraphy has been developed spanning the last 300,000 yr. The chronology is developed using a stacked oxygen-isotope stratigraphy and four different orbital tuning approaches, each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data. Each approach yields a separate chronology. The error measured by the standard deviation about the average of these four results (which represents the “best” chronology) has an average magnitude of only 2500 yr. This small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used. Excellent convergence between chronologies developed using each of five different paleoclimatological indicators (from a single core) is also obtained. The resultant chronology is also insensitive to the specific indicator used. The error associated with each tuning approach is estimated independently and propagated through to the average result. The resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr, in excellent agreement with the 2500-yr estimate. Transfer of the final chronology to the stacked record leads to an estimated error of ±1500 yr. Thus the final chronology has an average error of ±5000 yr.

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

Since 1968, cruises of the D.V. Glomar Challenger have created a vast and immensely valuable collection of core samples and geologic data for hundreds of drill sites in all oceans and in the Caribbean, Mediterranean, and Red Seas. This collection represents a large part of the Cenozoic and Mesozoic record of the oceans. The material enables us to reconstruct the geologic history of the ocean basins and improve our understanding of the history of the Earth, the evolution of life, temporal changes in oceanic circulation, and indirectly, the evaluation of the Earth's climate. Regional syntheses are indispensable for effective planning for future ocean drilling. Our study provides a synthesis of the data available for the central equatorial Pacific Ocean, with emphasis on the depositional history of pelagic biogenic sediment and its control by tectonic events and paleoceanographic conditions. AbstractThis study has three distinct but interrelated objectives: to prepare a geological synthesis of Deep Sea Drilling Project data from the central equatorial Pacific Ocean, to interpret this information in terms of the paleoceanographic history of this region, and to evaluate the usefulness of drill data and develop procedures and strategies for future studies of this kind. The investigation is based on primary data contained in the Initial Reports of the Deep Sea Drilling Project and is supported by information from surface cores. The principal data used are the biostratigraphy, lithology, carbonate content, bulk density, and porosity of the cores. From these properties, sedimentation rates, carbonate and carbonate-free accumulation rates, and paleobathymetric histories of the drill sites were derived with the aid of Berggren's chronology. Paleopositions of the drill sites and surface cores were determined from rotation parameters of the Pacific and Cocos plates.The present surface and deep circulation, fertility patterns, and sedimentation of the equatorial Pacific constitute a frame of reference for the paleoceanographic evolution. East-west and north-south lithologic profiles show that a zone of maximum deposition approximately parallel to the Equator has existed at least since middle Eocene time. With increasing age, the axis of this zone is found progressively farther north of the Equator. The profiles illustrate a gradual change from calcareous to siliceous deposits with increasing depth at any time, and they indicate an abrupt change from a dominantly siliceous to a dominantly calcareous depositional regime at the Eocene-Oligocene boundary. Large changes with time in the width and sedimentation rate of the calcareous equatorial zone indicate major variations in depositional conditions since Eocene time.Subsidence with age of the oceanic basement, plate rotation, and changes in spreading rate are closely examined in this study. A northward shift of the equatorial zone of maximum deposition with age and trend and ages of linear volcanic island chains (melting spots) define the rotation of the Pacific plate. This gives...

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Stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle Eocene samples (∼55 to ∼45 Ma) recently recovered from the Lomonosov Ridge by Integrated Ocean Drilling Program Expedition 302 (the Arctic Coring Expedition). The δ18O values of the Eocene samples ranged from −6.84‰ to −2.96‰ Vienna Peedee belemnite, with a mean value of −4.89‰, compared to 2.77‰ for a Miocene sample in the overlying section. An average salinity of 21 to 25‰ was calculated for the Eocene Arctic, compared to 35‰ for the Miocene, with lower salinities during the Paleocene Eocene thermal maximum, the Azolla event at ∼48.7 Ma, and a third previously unidentified event at ∼47.6 Ma. At the Azolla event, where the organic carbon content of the sediment reaches a maximum, a positive δ13C excursion was observed, indicating unusually high productivity in the surface waters.