Description: Integrated Ocean Drilling Program (IODP) Expedition 342 recovered exceptional Paleogene to early Neogene sedimentary archives from clay-rich sediments in the northwest Atlantic Ocean. These archives present an opportunity to study Cenozoic climate in a highly sensitive region at often unprecedented resolution. Such studies require continuous records in the depth and time domains. Using records from multiple adjacent drilled holes, intervals within consecutive cores are typically spliced into a single composite record on board the R/V JOIDES Resolution using high-resolution physical properties data sets acquired before the cores are split. The highly dynamic nature of the sediment drifts drilled during Expedition 342 and the modest amplitude of variance in the physical property records made it possible to construct only highly tentative initial working splices, which require extensive postexpedition follow-up work. Postexpedition, high-resolution X-ray fluorescence (XRF) core scanning data enabled the construction of a preliminary composite depth scale and splice. Here, we present the revised composite depth scale and splice for IODP Site U1406, predominantly constructed using detailed hole-to-hole correlations of newly generated high-resolution XRF data and revisions of the initial XRF data set. The revised composite depth scale and splice serve as a reference framework for future research on Site U1406 sediments.

Description: The interval spanning from the Early Eocene Climatic Optimum (EECO) to the onset of long-term cooling in the middle Eocene is marked by prominent changes in calcareous nannofossil assemblages and coincides with modification of the North Atlantic deep-ocean circulation. Here we present an integrated calcareous nannoplakton and bulk stable isotope records (δ18O and δ13C) across the early-middle Eocene (~52- 43 Ma) from IODP Site U1410 (northwest Atlantic), where middle Eocene deposits occur as clay-rich drift sediments reflecting the formation of persistent deep currents. Abundance patterns of selected biostratigraphically relevant taxa encompassing Ypresian-Lutetian calcareous nannofossil Zones CNE4-CNE12 served to test the biostratigraphic reliability of the species. In addition, long- and short-term trends documented in geochemical data have been used to determine the temporal relationships between palaeoenvironmental trends and changes in calcareous nannofossil assemblages. After the EECO to the Ypresian-Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm-water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. This prominent change occurred during a phase of relatively high δ18O values likely related to the post-EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the study middle Eocene interval, early Lutetian stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a temporary restoration of warmer conditions associated with an increase in abundance of D. sublodoensis. These results confirm previous records of environmental instability but the comparison of our results with different dataset highlights a global enigmatic scenario in term of bio-chemo-magnetostratigraphy.

Description: Fossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous-dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid-REE-enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources. This article is protected by copyright. All rights reserved.

Description: Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century (Haywood and Valdes, doi:10.1016/S0012-821X(03)00685-X) and atmospheric CO2 concentrations similar to today (Seki et al., 2010, doi:10.1016/j.epsl.2010.01.037; Bartoli et al., 2011, doi:10.1029/2010PA002055; Pagani et al., 2010, doi:10.1038/ngeo724). Estimates for global sea level highstands during these times (Miller et al., 2012, doi:10.1130/G32869.1) imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Description: The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

Description: The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today (doi:10.1130/0091-7613(1995)023〈1044:ECCALT〉2.3.CO;2, doi:10.1038/nature08399) and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume (doi:10.1016/j.gca.2003.09.002, doi:10.1038/ngeo1186). Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth's climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future (doi:10.1007/s10584-011-0156-z) as a consequence of unabated anthropogenic carbon emissions (doi:10.1038/ngeo1186, doi:10.1038/nature06588). Climatic conditions of the early Eocene 'greenhouse world', however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing.