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Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch
Pross, J철rg,Contreras, Lineth,Bijl, Peter K.,Greenwood, David R.,Bohaty, Steven M.,Schouten, Stefan,Bendle, James A.,R철hl, Ursula,Tauxe, Lisa,Raine, J. Ian,Huck, Claire E.,van de Flierdt, Tina,Jamieso Nature Publishing Group, a division of Macmillan P 2012 Nature Vol.488 No.7409
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 70째 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??째C) 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.
Reorganization of Southern Ocean Plankton Ecosystem at the Onset of Antarctic Glaciation
Houben, Alexander J. P.,Bijl, Peter K.,Pross, Jö,rg,Bohaty, Steven M.,Passchier, Sandra,Stickley, Catherine E.,Rö,hl, Ursula,Sugisaki, Saiko,Tauxe, Lisa,van de Flierdt, Tina,Olney, Matthew,San American Association for the Advancement of Scienc 2013 Science Vol.340 No.6130
<P><B>Southern Change</B></P><P>Antarctica has been mostly covered by ice since the inception of large-scale continental glaciation during the Oligocene, which profoundly altered the isotopic and mineralogical records of the sediments surrounding the continent. <B>Houben <I>et al.</I></B> (p. 341) found records of the corresponding living systems in the fossil marine dinoflagellate cysts, which revealed that a microplankton ecosystem, similar to the one that exists today, appeared simultaneously with the first major Antarctic glaciation approximately 34 million years ago.</P>
Cho, Hong Y.,Srinivasan, Abiraman,Hong, Joanna,Hsu, Eric,Liu, Shiguang,Shrivats, Arun,Kwak, Dan,Bohaty, Andrew K.,Paik, Hyun-jong,Hollinger, Jeffrey O.,Matyjaszewski, Krzysztof American Chemical Society 2011 Biomacromolecules Vol.12 No.10
<P>Star polymers with poly(ethylene glycol) (PEG) arms and a degradable cationic core were synthesized by the atom transfer radical copolymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate macromonomer (PEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a disulfide dimethacrylate (cross-linker, SS) via an “<I>arm-first</I>” approach. The star polymers had a diameter ∼15 nm and were degraded under redox conditions by glutathione treatment into individual polymeric chains due to cleavage of the disulfide cross-linker, as confirmed by dynamic light scattering. The star polymers were cultured with mouse calvarial preosteoblast-like cells, embryonic day 1, subclone 4 (MC3T3-E1.4) to determine biocompatibility. Data suggest star polymers were biocompatible, with ≥80% cell viability after 48 h of incubation even at high concentration (800 μg/mL). Zeta potential values varied with N/P ratio confirming complexation with siRNA. Successful cellular uptake of the star polymers in MC3T3-E1.4 cells was observed by confocal microscopy and flow cytometry after 24 h of incubation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/bomaf6/2011/bomaf6.2011.12.issue-10/bm2006455/production/images/medium/bm-2011-006455_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/bm2006455'>ACS Electronic Supporting Info</A></P>
A Cenozoic record of the equatorial Pacific carbonate compensation depth
P채like, Heiko,Lyle, Mitchell W.,Nishi, Hiroshi,Raffi, Isabella,Ridgwell, Andy,Gamage, Kusali,Klaus, Adam,Acton, Gary,Anderson, Louise,Backman, Jan,Baldauf, Jack,Beltran, Catherine,Bohaty, Steven M.,Bo Nature Publishing Group, a division of Macmillan P 2012 Nature Vol.488 No.7413
Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0??3.5??kilometres during the early Cenozoic (approximately 55??million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.