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  • Wiley  (2)
  • Geological Society of America (GSA)  (1)
  • American Association for the Advancement of Science (AAAS)
  • 2010-2014  (3)
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  • 1
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    Robust elements of Snowball Earth atmospheric circulation and oases for life (2013)
    Wiley
    Details
    Publication Date: 2013-06-06
    Description: [1]  Atmospheric circulation in a Snowball Earth is critical for determining cloud behavior, heat export from the tropics, regions of bare ice, and sea glacier flow. These processes strongly affect Snowball Earth deglaciation and the ability of oases to support photosynthetic marine life throughout a Snowball Earth. Here we establish robust aspects of the Snowball Earth atmospheric circulation by running six general circulation models with consistent Snowball Earth boundary conditions. The models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation. The strength of the Snowball Hadley circulation is roughly double modern at low CO 2 and greatly increases as CO 2 is increased. We force a 1D axisymmetric sea glacier model with GCM output and show that, neglecting zonal asymmetry, sea glaciers would limit ice thickness variations to O (10%). Global mean ice thickness in the 1D sea glacier model is well-approximated by a 0D ice thickness model with global mean surface temperature as the upper boundary condition. We then show that a thin-ice Snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the GCMs if we use ice optical properties that favor the thin-ice solution. Finally, we examine Snowball oases for life using analytical models forced by the GCM output and find that conditions become more favorable for oases as the Snowball warms, so that the most critical time for the survival of life would be near the beginning of a Snowball Earth episode.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Modeling the early Paleozoic long-term climatic trend (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-05-01
    Description: The early Paleozoic climate has been described as warm and equable. However, recent data based on conodont oxygen isotopic composition reveal a large, long, cooling trend through the Ordovician, followed by an abrupt cooling during the Late Ordovician glaciation. This long-term climate change is associated with a major radiation in the Earth life history. Nonetheless, the driving mechanisms for this cooling trend remain unknown. Carbon dioxide consumption by the weathering of fresh rocks from volcanic arcs has recently been suggested as a possible driver for this climate change. However, the impact of the plate motion context has not been explored yet, although it might have a major impact on atmospheric CO2 levels. Simulations with a climate model coupled to a biogeochemical model (GEOCLIM) show that the atmospheric CO2 decreased from more than 20 PAL ([~]5600 ppmv) in the Furongian down to approximately 10 PAL ([~]2800 ppmv) in the Llandovery before rising again in the Early Devonian. We suggest that changes in geography and exposure of fresh volcanic rocks on continents are required to explain the large CO2 drawdown that led to the onset of cooler to glacial conditions from the Middle Ordovician to the Llandovery. The weathering of fresh volcanic rocks is itself responsible for 33% of the Late Ordovician atmospheric CO2 decrease; the rest being related to the continent motion through the intertropical convergence zone (ITCZ). Mean annual continental temperature falls by 3{degrees}C in the Early Ordovician, reaching 13.5{degrees}C during the glacial interval, and rises to 16{degrees}C in the Early Devonian.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 3
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    Clouds and Snowball Earth deglaciation (2012)
    Wiley
    Details
    Publication Date: 2012-10-25
    Description: Neoproterozoic, and possibly Paleoproterozoic, glaciations represent the most extreme climate events in post-Hadean Earth, and may link closely with the evolution of the atmosphere and life. According to the Snowball Earth hypothesis, the entire ocean was covered with ice during these events for a few million years, during which time volcanic CO2 increased enough to cause deglaciation. Geochemical proxy data and model calculations suggest that the maximum CO2 was 0.01–0.1 by volume, but early climate modeling suggested that deglaciation was not possible at CO2 = 0.2. We use results from six different general circulation models (GCMs) to show that clouds could warm a Snowball enough to reduce the CO2 required for deglaciation by a factor of 10–100. Although more work is required to rigorously validate cloud schemes in Snowball-like conditions, our results suggest that Snowball deglaciation is consistent with observations.
    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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