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  • 1
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    Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-09-13
    Description: The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    The timescale of the silicate weathering negative feedback on atmospheric CO2 (2015)
    Wiley
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    Publication Date: 2015-04-09
    Description: The ultimate fate of CO 2 added to the ocean–atmosphere system is chemical reaction with silicate minerals and burial as marine carbonates. The timescale of this silicate weathering negative feedback on atmospheric p CO 2 will determine the duration of perturbations to the carbon cycle, be they geological release events or the current anthropogenic perturbation. However, there has been little previous work on quantifying the time-scale of the silicate weathering feedback, with the primary estimate of 300–400 kyr being traceable to an early box model study by Sundquist [1991]. Here we employ a representation of terrestrial rock weathering in conjunction with the ‘GENIE’ Earth System Model to elucidate the different timescales of atmospheric CO 2 regulation whilst including the main climate feedbacks on CO 2 uptake by the ocean. In this coupled model, the main dependencies of weathering – runoff, temperature and biological productivity – were driven from an energy-moisture balance atmosphere model and parameterized plant productivity. Long-term projections (1 Myr) were conducted for idealized scenarios of 1000 and 5000 PgC fossil fuel emissions and their sensitivity to different model parameters was tested. By fitting model output to a series of exponentials we determined the e -folding timescale for atmospheric CO 2 draw-down by silicate weathering to be ~240 kyr (range 170–380 kyr), significantly less than existing quantifications. Although the time-scales for re-equilibration of global surface temperature and surface ocean pH are similar to that for CO 2 , a much greater proportion of the peak temperature anomaly persists on this longest time-scale; ~21% compared to ~10% for CO 2 .
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Assessing the controllability of Arctic sea ice extent by sulfate aerosol geoengineering (2015)
    Wiley
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    Publication Date: 2015-01-24
    Description: In an assessment of how Arctic sea ice cover could be remediated in a warming world, we simulated the injection of SO 2 into the Arctic stratosphere making annual adjustments to injection rates. We treated one climate model realisation as a surrogate ‘real world’ with imperfect ‘observations’ and no re-running or reference to control simulations. SO 2 injection rates were proposed using a novel model predictive control regime which incorporated a second simpler climate model to forecast ‘optimal’ decision pathways. Commencing the simulation in 2018, Arctic sea ice cover was remediated by 2043 and maintained until solar geoengineering was terminated. We found quantifying climate side effects problematic because internal climate variability hampered detection of regional climate changes beyond the Arctic. Nevertheless, through decision maker learning and the accumulation of at least 10 years’ time series data exploited through an annual review cycle, uncertainties in observations and forcings were successfully managed.
    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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    Early Cenozoic Decoupling of Climate and Carbonate Compensation Depth Trends (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Our understanding of the long‐term evolution of the Earth system is based on the assumption that terrestrial weathering rates should respond to, and hence help regulate, atmospheric CO2 and climate. Increased terrestrial weathering requires increased carbonate accumulation in marine sediments, which in turn is expected to result in a long‐term deepening of the carbonate compensation depth (CCD). Here, we critically assess this long‐term relationship between climate and carbon cycling. We generate a record of marine deep‐sea carbonate abundance from selected late Paleocene through early Eocene time slices to reconstruct the position of the CCD. Although our data set allows for a modest CCD deepening, we find no statistically significant change in the CCD despite 〉3 °C global warming, highlighting the need for additional deep‐sea constraints on carbonate accumulation. Using an Earth system model, we show that the impact of warming and increased weathering on the CCD can be obscured by the opposing influences of ocean circulation patterns and sedimentary respiration of organic matter. From our data synthesis and modeling, we suggest that observations of warming, declining δ13C and a relatively stable CCD can be broadly reproduced by mid‐Paleogene increases in volcanic CO2 outgassing and weathering. However, remaining data‐model discrepancies hint at missing processes in our model, most likely involving the preservation and burial of organic carbon. Our finding of a decoupling between the CCD and global marine carbonate burial rates means that considerable care is needed in attempting to use the CCD to directly gauge global carbonate burial rates and hence weathering rates.
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    The geological record of ocean acidification (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-03-03
    Description: Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO(2), global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry-a consequence of the unprecedented rapidity of CO(2) release currently taking place.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Honisch, Barbel -- Ridgwell, Andy -- Schmidt, Daniela N -- Thomas, Ellen -- Gibbs, Samantha J -- Sluijs, Appy -- Zeebe, Richard -- Kump, Lee -- Martindale, Rowan C -- Greene, Sarah E -- Kiessling, Wolfgang -- Ries, Justin -- Zachos, James C -- Royer, Dana L -- Barker, Stephen -- Marchitto, Thomas M Jr -- Moyer, Ryan -- Pelejero, Carles -- Ziveri, Patrizia -- Foster, Gavin L -- Williams, Branwen -- New York, N.Y. -- Science. 2012 Mar 2;335(6072):1058-63. doi: 10.1126/science.1208277.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA. hoenisch@ldeo.columbia.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22383840" target="_blank"〉PubMed〈/a〉
    Keywords: Adaptation, Biological ; Animals ; *Aquatic Organisms ; Atmosphere ; Carbon Dioxide ; Carbonates/analysis ; *Ecosystem ; Extinction, Biological ; Forecasting ; Fossils ; *Geological Phenomena ; Hydrogen-Ion Concentration ; Oceans and Seas ; Seawater/*chemistry
    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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  • 6
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    Marine ecosystem responses to Cenozoic global change (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-08-03
    Description: The future impacts of anthropogenic global change on marine ecosystems are highly uncertain, but insights can be gained from past intervals of high atmospheric carbon dioxide partial pressure. The long-term geological record reveals an early Cenozoic warm climate that supported smaller polar ecosystems, few coral-algal reefs, expanded shallow-water platforms, longer food chains with less energy for top predators, and a less oxygenated ocean than today. The closest analogs for our likely future are climate transients, 10,000 to 200,000 years in duration, that occurred during the long early Cenozoic interval of elevated warmth. Although the future ocean will begin to resemble the past greenhouse world, it will retain elements of the present "icehouse" world long into the future. Changing temperatures and ocean acidification, together with rising sea level and shifts in ocean productivity, will keep marine ecosystems in a state of continuous change for 100,000 years.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Norris, R D -- Turner, S Kirtland -- Hull, P M -- Ridgwell, A -- New York, N.Y. -- Science. 2013 Aug 2;341(6145):492-8. doi: 10.1126/science.1240543.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA. rnorris@ucsd.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23908226" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biological Evolution ; *Climate Change/history ; *Ecosystem ; Greenhouse Effect ; History, Ancient ; *Oceans and Seas ; *Seawater ; Temperature ; Tidal Waves ; Vertebrates
    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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  • 7
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    A Cenozoic record of the equatorial Pacific carbonate compensation depth (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-08-31
    Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Palike, 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 -- Bown, Paul -- Busch, William -- Channell, Jim E T -- Chun, Cecily O J -- Delaney, Margaret -- Dewangan, Pawan -- Dunkley Jones, Tom -- Edgar, Kirsty M -- Evans, Helen -- Fitch, Peter -- Foster, Gavin L -- Gussone, Nikolaus -- Hasegawa, Hitoshi -- Hathorne, Ed C -- Hayashi, Hiroki -- Herrle, Jens O -- Holbourn, Ann -- Hovan, Steve -- Hyeong, Kiseong -- Iijima, Koichi -- Ito, Takashi -- Kamikuri, Shin-ichi -- Kimoto, Katsunori -- Kuroda, Junichiro -- Leon-Rodriguez, Lizette -- Malinverno, Alberto -- Moore, Ted C Jr -- Murphy, Brandon H -- Murphy, Daniel P -- Nakamura, Hideto -- Ogane, Kaoru -- Ohneiser, Christian -- Richter, Carl -- Robinson, Rebecca -- Rohling, Eelco J -- Romero, Oscar -- Sawada, Ken -- Scher, Howie -- Schneider, Leah -- Sluijs, Appy -- Takata, Hiroyuki -- Tian, Jun -- Tsujimoto, Akira -- Wade, Bridget S -- Westerhold, Thomas -- Wilkens, Roy -- Williams, Trevor -- Wilson, Paul A -- Yamamoto, Yuhji -- Yamamoto, Shinya -- Yamazaki, Toshitsugu -- Zeebe, Richard E -- England -- Nature. 2012 Aug 30;488(7413):609-14. doi: 10.1038/nature11360.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK. hpaelike@marum.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22932385" target="_blank"〉PubMed〈/a〉
    Keywords: *Altitude ; Atmosphere/chemistry ; Calcium Carbonate/*analysis ; *Carbon Cycle ; Carbon Dioxide/analysis ; Diatoms/metabolism ; Foraminifera/metabolism ; Geologic Sediments/chemistry ; Global Warming/history/statistics & numerical data ; History, 21st Century ; History, Ancient ; Marine Biology ; Oxygen/metabolism ; Pacific Ocean ; Seawater/*chemistry ; Temperature
    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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  • 8
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    Potential methane reservoirs beneath Antarctica (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-08-31
    Description: Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wadham, J L -- Arndt, S -- Tulaczyk, S -- Stibal, M -- Tranter, M -- Telling, J -- Lis, G P -- Lawson, E -- Ridgwell, A -- Dubnick, A -- Sharp, M J -- Anesio, A M -- Butler, C E H -- England -- Nature. 2012 Aug 30;488(7413):633-7. doi: 10.1038/nature11374.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK. j.l.wadham@bris.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22932387" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Feedback ; Gases/analysis/chemistry/metabolism ; Geologic Sediments/*chemistry/microbiology ; Global Warming ; Ice Cover ; Methane/*analysis/biosynthesis/chemistry ; Pressure ; Solubility ; Temperature ; Uncertainty
    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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  • 9
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    Climate–carbon cycle uncertainties and the Paris Agreement (2018)
    Springer Nature
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    Publication Date: 2018-06-26
    Description: Climate–carbon cycle uncertainties and the Paris Agreement Climate–carbon cycle uncertainties and the Paris Agreement, Published online: 25 June 2018; doi:10.1038/s41558-018-0197-7 A reasonable interpretation of the Paris Agreement may well still be technically achievable without the need for net negative emissions or excessively stringent policies according to climate–carbon-cycle modelling.
    Print ISSN: 1758-678X
    Electronic ISSN: 1758-6798
    Topics: Geosciences
    Published by Springer Nature
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  • 10
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    Nutrients as the dominant control on the spread of anoxia and euxinia across the Cenomanian-Turonian oceanic anoxic event (OAE2): Model-data comparison (2012)
    Wiley
    Details
    Publication Date: 2012-12-15
    Description: The Cenomanian-Turonian oceanic anoxic event (OAE2) is characterized by large perturbations in the oxygen and sulfur cycles of the ocean, potentially resulting from changes in oxygen supply (via oxygen solubility and ocean circulation) and in marine productivity. We assess the relative impact of these mechanisms, comparing model experiments with a new compilation of observations for seafloor dysoxia/anoxia and photic zone euxinia. The model employed is an intermediate-complexity Earth system model which accounts for the main ocean dynamics and biogeochemistry of the Cretaceous climate. The impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations. The model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with OAE2. Observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content (responsible for 85% of the change). Higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments, which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation. The model also shows that the presence of seafloor anoxia, as suggested by black-shale deposition in the proto-North Atlantic Ocean before the event, might be the result of the silled shape and lack of deep-water formation of this basin at the Late Cretaceous. Overall our model-data comparison shows that OAE2 anoxia was quasi-global spreading from 5% of the ocean volume before the event to at least 50% during OAE2.
    Print ISSN: 0883-8305
    Electronic ISSN: 1944-9186
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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