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 and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. 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 as a consequence of unabated anthropogenic carbon emissions. 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.

Citation for published item: t miesonD F F F nd ieliD eF nd vivingstoneD FtF nd ¡ y gof ighD gF nd tokesD gF F nd rillen r ndD gEhF nd howdeswellD tFeF @PHIPA 9s eEstre m st ility on reverse ed slopeF9D x ture geos ien eFD S @IIAF ppF UWWEVHPF Further information on publisher's website: httpXGGdxFdoiForgGIHFIHQVGngeoITHH Publisher's copyright statement:Additional information:Read Durham University's press release about this article, available at:http://www.dur.ac.uk/news/newsitem/?itemno=15572 Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Ice streams are fast-flowing arteries of ice sheets that dominate ice discharge into the oceans, impacting directly upon sea level. Many ice streams possess beds that are below sea level and typically deepen inland on a reverse-slope 9 . Theory suggests that ice discharge increases rapidly with water depth 3 , and in the absence of lateral-drag induced buttressing from a floating ice shelf, grounding lines (marking the transition from grounded to floating ice) on reverse-bed slopes may be unstable 1-2 . Bed topography is therefore cited as a strong control on ice-stream retreat rate 3,10 and modern satellite observations of rapid ice-stream thinning and recession appear consistent with this theory 4-6 . However, with just two decades of data, these records are too short to identify the longerterm centennial to millennial-scale trends crucial for constraining future sea-level projections.Major uncertainties in predictions of ice-sheet vulnerability 11 relate to limitations in understanding processes controlling grounding-line motion and, importantly, to deficiencies in grounding-line treatment in ice-sheet models 12 . In recent years, significant advances in model development have been made 3,12-17 , but tests have only been applied to simplified bed geometries or to steady-state conditions and lack validation against data over timescales longer than a few decades. We aim to understand the long-term controls and stability of marine ice streams and, for the first time, 'pinning points' (e.g. at 500 km; Fig. 2). However, in the reverse-sloping portion of the bed and, significantly, in the absence of topographic highs, several slow-downs also occur. Moreover, the simulated stabilisations are broadly consistent with previously mapped GZW positions (Fig. 2).These short-term changes in retreat-rate occur adjacent to GZWs 1, 2, 3, 6, 7 and 8 and prolonged grounding-line stability is modelled between GZWs 4 and 5 where the reverse slope steepens into the overdeepened portion of Marguerite Trough...

We present a reconstruction of the Antarctic topography at the Eocene-Oligocene (ca. 34 Ma) climate transition. This provides a realistic key boundary condition for modeling the first big Antarctic ice sheets at this time instead of using the present day bedrock topography, which has changed significantly from millions of years of tectonism and erosion. We reconstruct topography using a set of tools including ice sheet-erosion models, models of thermal subsidence and plate movement. Erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy. Maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty. Our results point to a significant upland area in the Ross Sea/Marie Byrd Land and Weddell Sea sectors. In addition, East Antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets. Parts of East Antarctica have not changed since the E-O boundary because they were protected under non-erosive cold-based ice. The reconstructions provide a better-defined boundary condition for modeling that seeks to understand interaction between the Antarctic ice sheet and climate, along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations.

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Bentley, M. J., Ocofaigh, C., Anderson, J. B., Conway, H., Davies, B., Graham, A. G. C., Hillenbrand, C. D., Hodgson, D. A., Jamieson, S. S. R., Larter, R. D., Mackintosh, A., Smith, J. A., Verleyen, E., Ackert, R. P., Bart, P. J., Berg, S., Brunstein, D., Canals, M., Colhoun, E. A., Crosta, X., Dickens, W. A., Domack, E., Dowdeswell, J. A., Dunbar, R., Ehrmann, W., Evans, J., Favier, V., Fink, D., Fogwill, C. J., Glasser, N. F., Gohl, K., Golledge, N. R., Goodwin, I., Gore, D. B., Greenwood, S. L., Hall, B. L., Hall, K., Hedding, D. W., Hein, A. S., Hocking, E. P., Jakobsson, M., Johnson, J. S., Jomelli, V., Jones, R. S., Klages, J. P., Kristoffersen, Y., Kuhn, G., Leventer, A., Licht, K., Lilly, K., Lindow, J., Livingstone, S. J., Mass?, G., McGlone, M. S., McKay, R. M., Melles, M., Miura, H., Mulvaney, R., Nel, W., Nitsche, F. O., O'Brien, P. E., Post, A. L., Roberts, S. J., Saunders, K. M., Selkirk, P. M., Simms, A. R., Spiegel, C., Stolldorf, T. D., Sugden, D. E., van der Putten, N., van Ommen, T., Verfaillie, D., Vyverman, W., Wagner, B., White, D. A., Witus, A. E. Zwartz, D. (2014). A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum. Quaternary Science Reviews, 100, 1-9.A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community. (C) 2014 The Authors. Published by Elsevier Ltd.publishersversionPeer reviewe