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  • 1
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    Understanding long-term carbon cycle trends: The late paleocene through the early eocene (2013)
    Wiley
    Details
    Publication Date: 2013-09-20
    Description: [1]  The late Paleocene to the early Eocene (~58-52 Ma) was marked by significant changes in global climate and carbon cycling. Among evidence for these changes, stable isotope records reveal prominent decreases in δ 18 O and δ 13 C, suggesting a rise in temperature on Earth's surface (~4 °C) and a drop in net carbon output from the ocean and atmosphere. Concurrently, deep-sea carbonate records at several sites indicate a deepening of the calcite compensation depth (CCD). Here, we investigate possible causes (e.g., increased volcanic degassing, decreased net organic burial, and accelerated dissociation of gas hydrate) for these observations, but from a new perspective. The basic model employed is a modified version of GEOCARB III. However, we have coupled this well-known geochemical model to LOSCAR, a model that enables simulation of seawater carbonate chemistry, the CCD, and ocean δ 13 C. We have also added a capacitor, in this case presented by gas hydrates, that can store and release 13 C-depleted carbon to and from the shallow geosphere over millions of years. We further consider accurate input data (e.g., δ 13 C of carbonate) on a currently accepted time scale that spans an interval much longer than the perturbation. Several different scenarios are investigated with the goal of consistency amongst inferred changes in temperature, the CCD, and surface ocean and deep ocean δ 13 C. The results strongly suggest that a decrease in net organic carbon burial drove carbon cycle changes during the late Paleocene and early Eocene, although an increase in volcanic activity might have contributed. Importantly, a drop in net organic carbon burial may represent increased oxidation of previously deposited organic carbon, such as stored in peat or gas hydrates. The model successfully recreates trends in Earth surface warming, as inferred from δ 18 O records, the CCD, and δ 13 C. At the moment, however, our coupled modeling effort cannot reproduce the magnitude of change in all these records collectively. Similar problems have arisen in simulations of short-term hyperthermal events during the early Paleogene (PETM), suggesting one or more basic issues with data interpretation or geochemical modeling remain.
    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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    The Source and Fate of Massive Carbon Input During the Latest Paleocene Thermal Maximum (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-11-24
    Description: Lithologic, faunal, seismic, and isotopic evidence from the Blake Nose (subtropical western North Atlantic) links a massive release of biogenic methane approximately 55.5 million years ago to a warming of deep-ocean and high-latitude surface waters, a large perturbation in the combined ocean-atmosphere carbon cycle (the largest of the past 90 million years), a mass extinction event in benthic faunas, and a radiation of mammalian orders. The deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming, massive carbon input to the global exogenic carbon cycle, pelagic carbonate dissolution, a decrease in dissolved oxygen, and a benthic foraminiferal extinction event. These events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the Blake Nose as a site of methane release.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Katz -- Pak -- Dickens -- Miller -- New York, N.Y. -- Science. 1999 Nov 19;286(5444):1531-1533.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854, USA. Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA. School of Earth Sciences, James Cook University, Townsville, Queensland 4811, Australia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10567252" 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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  • 3
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    An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-01-19
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zachos, James C -- Dickens, Gerald R -- Zeebe, Richard E -- England -- Nature. 2008 Jan 17;451(7176):279-83. doi: 10.1038/nature06588.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, University of California at Santa Cruz, Santa Cruz, California 95060, USA. jzachos@es.ucsc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18202643" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere/chemistry ; Carbon/analysis/*metabolism ; Carbon Dioxide/analysis/metabolism ; Ecosystem ; *Greenhouse Effect ; History, 21st Century ; History, Ancient ; Human Activities ; Models, Theoretical ; Oceans and Seas ; Temperature ; Time Factors
    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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  • 4
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    Distributions of microbial activities in deep subseafloor sediments (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-12-25
    Description: Diverse microbial communities and numerous energy-yielding activities occur in deeply buried sediments of the eastern Pacific Ocean. Distributions of metabolic activities often deviate from the standard model. Rates of activities, cell concentrations, and populations of cultured bacteria vary consistently from one subseafloor environment to another. Net rates of major activities principally rely on electron acceptors and electron donors from the photosynthetic surface world. At open-ocean sites, nitrate and oxygen are supplied to the deepest sedimentary communities through the underlying basaltic aquifer. In turn, these sedimentary communities may supply dissolved electron donors and nutrients to the underlying crustal biosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉D'Hondt, Steven -- Jorgensen, Bo Barker -- Miller, D Jay -- Batzke, Anja -- Blake, Ruth -- Cragg, Barry A -- Cypionka, Heribert -- Dickens, Gerald R -- Ferdelman, Timothy -- Hinrichs, Kai-Uwe -- Holm, Nils G -- Mitterer, Richard -- Spivack, Arthur -- Wang, Guizhi -- Bekins, Barbara -- Engelen, Bert -- Ford, Kathryn -- Gettemy, Glen -- Rutherford, Scott D -- Sass, Henrik -- Skilbeck, C Gregory -- Aiello, Ivano W -- Guerin, Gilles -- House, Christopher H -- Inagaki, Fumio -- Meister, Patrick -- Naehr, Thomas -- Niitsuma, Sachiko -- Parkes, R John -- Schippers, Axel -- Smith, David C -- Teske, Andreas -- Wiegel, Juergen -- Padilla, Christian Naranjo -- Acosta, Juana Luz Solis -- New York, N.Y. -- Science. 2004 Dec 24;306(5705):2216-21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ocean Drilling Program Leg 201 Shipboard Scientific Party, NASA Astrobiology Institute, University of Rhode Island Graduate School of Oceanography, South Ferry Road, Narragansett, RI 02882, USA. dhondt@gso.uri.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15618510" target="_blank"〉PubMed〈/a〉
    Keywords: Bacteria/growth & development/isolation & purification/*metabolism ; Carbon/metabolism ; Colony Count, Microbial ; *Ecosystem ; Electron Transport ; Geologic Sediments/*microbiology ; Iron/metabolism ; Manganese/metabolism ; Methane/metabolism ; Nitrates/metabolism ; Oxidants/metabolism ; Oxidation-Reduction ; Pacific Ocean ; Peru ; Photosynthesis ; Seawater/chemistry ; Sulfates/metabolism ; Thermodynamics
    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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  • 5
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    Dynamic simulations of potential methane release from East Siberian continental slope sediments (2016)
    Wiley
    Details
    Publication Date: 2016-02-18
    Description: Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH 4 ) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3°C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH 4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 gigaton (Gt) of CH 4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH 4 discharge becomes significantly smaller (to ∼0.05 Gt) if glacial sea-level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH 4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH 4 inputs from other sources. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Onset of carbon isotope excursion at the Paleocene-Eocene thermal maximum took millennia, not 13 years (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-02-26
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    PETM onset took millennia, not 13 years [Physical Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-03-26
    Description: The Paleocene-Eocene thermal maximum (PETM) may represent the best paleo-analog for rapid and massive carbon release to the ocean and atmosphere. Thus, constraining the carbon release rate at its onset is critical. Wright and Schaller (1) use records from apparently rhythmically layered shelf sediments to argue that the layering is...
    Keywords: Letters
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Continental arc-island arc fluctuations, growth of crustal carbonates, and long-term climate change (2013)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2013-01-29
    Description: The Cretaceous to early Paleogene (ca. 140–50 Ma) was characterized by a greenhouse baseline climate, driven by elevated concentrations of atmospheric CO 2 . Hypotheses for the elevated CO 2 concentrations invoke an increase in volcanic CO 2 production due to higher oceanic crust production rates, higher frequency of large igneous provinces, or increases in pelagic carbonate deposition, the last leading to enhanced carbonate subduction into the mantle source regions of arc volcanoes. However, these are not the only volcanic sources of CO 2 during this time interval. We show here that ocean-continent subduction zones, manifested as a global chain of continental arc volcanoes, were as much as 200% longer in the Cretaceous and early Paleogene than in the late Paleogene to present, when a cooler climate prevailed. In particular, many of these continental arcs, unlike island arcs, intersected ancient continental platform carbonates stored on the continental upper plate. We show that the greater length of Cretaceous–Paleogene continental arcs, specifically carbonate-intersecting arcs, could have increased global production of CO 2 by at least 3.7–5.5 times that of the present day. This magmatically driven crustal decarbonation flux of CO 2 through continental arcs exceeds that delivered by Cretaceous oceanic crust production, and was sufficient to drive Cretaceous–Paleogene greenhouse conditions. Thus, carbonate-intersecting continental arc volcanoes likely played an important role in driving greenhouse conditions in the Cretaceous–Paleogene. If so, the waning of North American and Eurasian continental arcs in the Late Cretaceous to early Paleogene, followed by a fundamental shift in western Pacific subduction zones ca. 52 Ma to an island arc–dominated regime, would have been manifested as a decline in global volcanic CO 2 production, prompting a return to an icehouse baseline in the Neogene. Our analysis leads us to speculate that long-term (〉50 m.y.) greenhouse-icehouse oscillations may be linked to fluctuations between continental- and island arc–dominated states. These tectonic fluctuations may result from large-scale changes in the nature of subduction zones, changes we speculate may be tied to the assembly and dispersal of continents. Specifically, dispersal of continents may drive the leading edge of continents to override subduction zones, resulting in continental arc volcanism, whereas assembly of continents or closing of large ocean basins may be manifested as large-scale slab rollback, resulting in the development of intraoceanic volcanic arcs. We suggest that greenhouse-icehouse oscillations are a natural consequence of plate tectonics operating in the presence of continental masses, serving as a large capacitor of carbonates that can be episodically purged during global flare-ups in continental arcs. Importantly, if the global crustal carbonate reservoir has grown with time, as might be expected because platform carbonates on continents do not generally subduct, the greenhouse-driving potential of continental arcs would have been small during the Archean, but would have increased in the Neoproterozoic and Phanerozoic after a significant reservoir of crustal carbonates had formed in response to the evolution of life and the growth of continents.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Generalization of gas hydrate distribution and saturation in marine sediments by scaling of thermodynamic and transport processes (2007)
    American Journal of Science
    Details
    Publication Date: 2007-06-01
    Print ISSN: 0002-9599
    Electronic ISSN: 1945-452X
    Topics: Geosciences
    Published by American Journal of Science
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  • 10
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    Understanding long-term carbon cycle trends: The late Paleocene through the early Eocene (2013)
    American Geophysical Union
    Details
    Publication Date: 2013-11-11
    Print ISSN: 2572-4517
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by American Geophysical Union
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