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  • 1
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    Late Cretaceous climate simulations with different CO2 levels and subarctic gateway configurations: A model – data comparison (2017)
    Wiley
    Details
    Publication Date: 2017-08-29
    Description: We investigate the impact of different CO 2 levels and different subarctic gateway configurations on the surface temperatures during the latest Cretaceous using the Earth System Model COSMOS. The simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest Cretaceous proxies. In our numerical experiments, the CO 2 level ranges from 1 to 6 x the pre-industrial (PI) CO 2 level of 280 ppm. On a global scale, the most reasonable match between modelling and proxy data is obtained for the experiments with 3 to 5 x PI CO 2 concentrations. However, the simulated low (high) latitude temperatures are too high (low) as compared to the proxy data. The moderate CO 2 levels scenarios might be more realistic, if we take into account proxy data and the dead zone effect criterion. Furthermore, we test if the model-data discrepancies can be caused by too simplistic proxy-data interpretations. This is distinctly seen at high latitudes, where most proxies are biased towards summer temperatures. Additional sensitivity experiments with different ocean gateway configurations and constant CO 2 level indicate only minor surface temperatures changes (〈~1°C) on a global scale, with higher values (up to ~8°C) on a regional scale. These findings imply that modelled and reconstructed temperature gradients are to a large degree only qualitatively comparable, providing challenges for the interpretation of proxy data and/or model sensitivity. With respect to the latter, our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the mid latitudes.
    Print ISSN: 0883-8305
    Electronic ISSN: 1944-9186
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Ribosome–NatA architecture reveals that rRNA expansion segments coordinate N-terminal acetylation (2018)
    Springer Nature
    Details
    Publication Date: 2018
    Print ISSN: 1545-9993
    Electronic ISSN: 1545-9985
    Topics: Biology , Medicine
    Published by Springer Nature
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  • 3
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    A warm Miocene climate at low atmospheric CO2 levels (2011)
    Wiley
    Details
    Publication Date: 2011-10-27
    Description: Proxy records from the Miocene epoch (∼23-5 Ma) indicate a warmer climate than today in spite of lower atmospheric carbon dioxide (CO2) concentrations in the range of preindustrial levels. As yet the simulation of a warm Miocene climate with these low CO2 values has proven to be a challenge. In this study we present climate simulations of the Late Miocene (11-7 Ma) with a preindustrial CO2 level, using a coupled atmosphere-ocean general circulation model (AOGCM). The simulated global mean surface temperature of ∼17.8 °C represents a significantly warmer climate than today. We have analyzed the relative importance of tectonic and vegetation changes as forcing factors. We find that the strongest temperature increase is due to the Late Miocene vegetation distribution, which is more than three times stronger than the impact induced by tectonic alterations. Furthermore, a combination of both forcing factors results in a global temperature increase which is lower than the sum of the individual forcing effects. Energy balance estimates suggest that a reduction in the planetary albedo and a positive water vapor feedback in a warmer atmosphere are the dominating mechanisms to explain the temperature increase. Each of these factors contributes about one half to the global temperature rise of ∼3 K. Our results suggest that a much warmer climate during the Late Miocene can be reconciled with CO2 concentrations similar to preindustrial values.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Interhemispheric Atlantic seesaw response during the last deglaciation (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-02-27
    Description: The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean. Here we present new records from the South Atlantic that show rapid changes during the last deglaciation that were instantaneous (within dating uncertainty) and of opposite sign to those observed in the North Atlantic. Our results demonstrate a direct link between the abrupt changes associated with variations in the Atlantic meridional overturning circulation and the more gradual adjustments characteristic of the Southern Ocean. These results emphasize the importance of the Southern Ocean for the development and transmission of millennial-scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barker, Stephen -- Diz, Paula -- Vautravers, Maryline J -- Pike, Jennifer -- Knorr, Gregor -- Hall, Ian R -- Broecker, Wallace S -- England -- Nature. 2009 Feb 26;457(7233):1097-102. doi: 10.1038/nature07770.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3YE, UK. barkers3@cf.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19242468" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Atlantic Ocean ; Atmosphere/chemistry ; Carbon Dioxide/analysis ; Greenhouse Effect ; Greenland ; History, Ancient ; *Ice Cover ; Plankton/metabolism ; Seawater/analysis ; *Temperature ; *Water Movements
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Abrupt glacial climate shifts controlled by ice sheet changes (2014)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2014-08-15
    Description: During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhang, Xu -- Lohmann, Gerrit -- Knorr, Gregor -- Purcell, Conor -- England -- Nature. 2014 Aug 21;512(7514):290-4. doi: 10.1038/nature13592. Epub 2014 Aug 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bussestrasse 24, D-27570 Bremerhaven, Germany. ; 1] Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bussestrasse 24, D-27570 Bremerhaven, Germany [2] MARUM-Center for Marine Environmental Sciences, University Bremen, Leobener Strasse, D-28359 Bremen, Germany. ; 1] Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bussestrasse 24, D-27570 Bremerhaven, Germany [2] School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25119027" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 6
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    Icebergs not the trigger for North Atlantic cold events (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-04-17
    Description: Abrupt climate change is a ubiquitous feature of the Late Pleistocene epoch. In particular, the sequence of Dansgaard-Oeschger events (repeated transitions between warm interstadial and cold stadial conditions), as recorded by ice cores in Greenland, are thought to be linked to changes in the mode of overturning circulation in the Atlantic Ocean. Moreover, the observed correspondence between North Atlantic cold events and increased iceberg calving and dispersal from ice sheets surrounding the North Atlantic has inspired many ocean and climate modelling studies that make use of freshwater forcing scenarios to simulate abrupt change across the North Atlantic region and beyond. On the other hand, previous studies identified an apparent lag between North Atlantic cooling events and the appearance of ice-rafted debris over the last glacial cycle, leading to the hypothesis that iceberg discharge may be a consequence of stadial conditions rather than the cause. Here we further establish this relationship and demonstrate a systematic delay between pronounced surface cooling and the arrival of ice-rafted debris at a site southwest of Iceland over the past four glacial cycles, implying that in general icebergs arrived too late to have triggered cooling. Instead we suggest that--on the basis of our comparisons of ice-rafted debris and polar planktonic foraminifera--abrupt transitions to stadial conditions should be considered as a nonlinear response to more gradual cooling across the North Atlantic. Although the freshwater derived from melting icebergs may provide a positive feedback for enhancing and or prolonging stadial conditions, it does not trigger northern stadial events.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barker, Stephen -- Chen, James -- Gong, Xun -- Jonkers, Lukas -- Knorr, Gregor -- Thornalley, David -- England -- Nature. 2015 Apr 16;520(7547):333-6. doi: 10.1038/nature14330.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK. ; Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bussestrasse 24, D-27570 Bremerhaven, Germany. ; 1] Department of Geography, University College London, London WC1E 6BT, UK. [2] Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25877202" target="_blank"〉PubMed〈/a〉
    Keywords: Atlantic Ocean ; Climate Change/*history ; *Cold Temperature ; Foraminifera/isolation & purification ; Greenland ; History, Ancient ; *Ice Cover ; Iceland ; Models, Theoretical ; Time Factors ; Water Movements
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 7
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    800,000 years of abrupt climate variability (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-09-10
    Description: We constructed an 800,000-year synthetic record of Greenland climate variability based on the thermal bipolar seesaw model. Our Greenland analog reproduces much of the variability seen in the Greenland ice cores over the past 100,000 years. The synthetic record shows strong similarity with the absolutely dated speleothem record from China, allowing us to place ice core records within an absolute timeframe for the past 400,000 years. Hence, it provides both a stratigraphic reference and a conceptual basis for assessing the long-term evolution of millennial-scale variability and its potential role in climate change at longer time scales. Indeed, we provide evidence for a ubiquitous association between bipolar seesaw oscillations and glacial terminations throughout the Middle to Late Pleistocene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barker, Stephen -- Knorr, Gregor -- Edwards, R Lawrence -- Parrenin, Frederic -- Putnam, Aaron E -- Skinner, Luke C -- Wolff, Eric -- Ziegler, Martin -- New York, N.Y. -- Science. 2011 Oct 21;334(6054):347-51. doi: 10.1126/science.1203580. Epub 2011 Sep 8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK. barkers3@cf.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21903776" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Long-term pattern and magnitude of soil carbon feedback to the climate system in a warming world (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-10-06
    Description: In a 26-year soil warming experiment in a mid-latitude hardwood forest, we documented changes in soil carbon cycling to investigate the potential consequences for the climate system. We found that soil warming results in a four-phase pattern of soil organic matter decay and carbon dioxide fluxes to the atmosphere, with phases of substantial soil carbon loss alternating with phases of no detectable loss. Several factors combine to affect the timing, magnitude, and thermal acclimation of soil carbon loss. These include depletion of microbially accessible carbon pools, reductions in microbial biomass, a shift in microbial carbon use efficiency, and changes in microbial community composition. Our results support projections of a long-term, self-reinforcing carbon feedback from mid-latitude forests to the climate system as the world warms.
    Keywords: Ecology, Microbiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Evolution of Global Ocean Tide Levels Since the Last Glacial Maximum (2023)
    Details
    Publication Date: 2023-07-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This study addresses the evolution of global tidal dynamics since the Last Glacial Maximum focusing on the extraction of tidal levels that are vital for the interpretation of geologic sea‐level markers. For this purpose, we employ a truly‐global barotropic ocean tide model which considers the non‐local effect of Self‐Attraction and Loading. A comparison to a global tide gauge data set for modern conditions yields agreement levels of 65%–70%. As the chosen model is data‐unconstrained, and the considered dissipation mechanisms are well understood, it does not have to be re‐tuned for altered paleoceanographic conditions. In agreement with prior studies, we find that changes in bathymetry during glaciation and deglaciation do exert critical control over the modeling results with minor impact by ocean stratification and sea ice friction. Simulations of 4 major partial tides are repeated in time steps of 0.5–1 ka and augmented by 4 additional partial tides estimated via linear admittance. These are then used to derive time series from which the tidal levels are determined and provided as a global data set conforming to the HOLSEA format. The modeling results indicate a strengthened tidal resonance by M〈sub〉2〈/sub〉, but also by O〈sub〉1〈/sub〉, under glacial conditions, in accordance with prior studies. Especially, a number of prominent changes in local resonance conditions are identified, that impact the tidal levels up to several meters difference. Among other regions, resonant features are predicted for the North Atlantic, the South China Sea, and the Arctic Ocean.〈/p〉
    Description: Plain Language Summary: We discuss changes in ocean tides during the last 21,000 years. This time marks the Last Glacial Maximum when large parts of the Earth's surface were covered by ice and the sea level was more than 100 m lower than today. Such a low sea level means that many regions of the Earth became land and the ocean's depth changed markedly. The distribution of land and water dominates changes in the tidal levels like the spring or neap tide. With a tidal computer model recently developed by our group, we determine these tidal levels for different times steps from 21,000 years to today. Tidal levels are important for geologists who want to understand former sea level changes with samples found at ancient shorelines. As many of such samples were deposited at a specific tidal level, our modeled information will help them to relate their height to the mean sea‐level. Of course, our model is not the only one that can estimate such changes, but we discuss the advantages of our recent development over previous tools available.〈/p〉
    Description: Key Points: Evolution of four major partial tides from Last Glacial Maximum until present times.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Validation of the employed ocean tide model with present‐day tide gauge data and dissipation rates.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Diligent derivation of global tidal levels for the interpretation of sea level indexpoints.〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.46 ; ocean tide modeling ; tidal dissipation ; tidal levels ; indicative range ; sea level index points ; numerical modeling
    Language: English
    Type: doc-type:article
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  • 10
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    Charge separation at a plasma edge in the presence of a density gradient (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-06-01
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics
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