• Carbon, climate change and ocean anoxia

    From ScienceDaily@1:317/3 to All on Monday, May 02, 2022 22:30:42
    Carbon, climate change and ocean anoxia in an ancient icehouse world


    Date:
    May 2, 2022
    Source:
    University of California - Davis
    Summary:
    A new study describes a period of rapid global climate change
    in an ice- capped world much like the present -- but 304 million
    years ago. Within about 300,000 years, atmospheric carbon dioxide
    levels doubled, oceans became anoxic, and biodiversity dropped on
    land and at sea.



    FULL STORY ==========================================================================
    A new study describes a period of rapid global climate change in
    an ice-capped world much like the present -- but 304 million years
    ago. Within about 300,000 years, atmospheric carbon dioxide levels
    doubled, oceans became anoxic, and biodiversity dropped on land and
    at sea.


    ==========================================================================
    "It was one of the fastest warming events in Earth's history," said
    Isabel Montan~ez, distinguished professor in the Department of Earth
    and Planetary Sciences at the University of California, Davis.

    Although several other 'hyperthermal' or rapid warming events are known
    in Earth's history, this is the first identified in an icehouse Earth,
    when the planet had ice caps and glaciers, comparable to the present
    day. It shows that an icehouse climate may be more sensitive to changes
    in atmospheric carbon dioxide than warmer conditions, when CO2levels are already higher. The work is published this week (May 2) in Proceedings
    of the National Academy of Sciences.

    Montan~ez' lab has studied the period from 300 million to 260 million
    years ago, when Earth's climate went from a glacial icehouse to a hot,
    ice-free greenhouse. In 2007, they showed that the climate swung back
    and forth several times during this period.

    More recently, Montan~ez' team and others have been able to home in on
    a transition 304 million years ago, the Kasimovian-Gzhelian boundary
    or KGB. They used multiple proxies, including carbon isotopes and
    trace elements from rocks and plant fossils, and modeling to estimate atmospheric CO2 at the time.

    The researchers estimate that about 9000 Gigatons of carbon were released
    into the atmosphere just before the K-G boundary.



    ==========================================================================
    "We don't have a rate, but it was one of the fastest in Earth's history," Montan~ez said. That doubled atmospheric CO2from approximately 350 parts
    per million, comparable to modern pre-industrial levels, to about 700 ppm.

    Deep ocean dead zones One of the consequences of global warming is marine anoxia, or a drop in dissolved oxygen in the ocean. Melting ice caps
    release fresh water onto the ocean surface, creating a barrier to deep
    water circulation and cutting off the supply of oxygen. Without oxygen,
    marine life dies.

    Lack of oxygen leaves its mark in uranium isotopes incorporated into
    rocks forming at the bottom of the ocean. By measuring uranium isotopes
    in carbonate rocks in present-day China, the researchers could get a
    proxy for the amount of oxygen -- or lack of it -- in the ocean when
    those rocks were laid down.

    About 23 percent of the seafloor worldwide became anoxic dead zones,
    they estimate. That lines up with other studies showing big losses in biodiversity on land and at sea at the same time.



    ==========================================================================
    The effect of carbon release on ocean anoxia was significantly greater
    than that seen in other studies of rapid warming during 'greenhouse' conditions.

    That may be because the baseline level of atmospheric CO2 was already
    much higher.

    "If you raised CO2 by the same amount in a greenhouse world, there isn't
    much affect, but icehouses seem to be much more sensitive to change and
    marine anoxia," Montan~ez said.

    The massive carbon release may have been triggered by volcanic eruptions
    that tore through carboniferous coal beds, Montan~ez said. The eruptions
    would also have started fires, and warming may have melted permafrost,
    leading to the release of more organic carbon.

    Montan~ez is co-corresponding author on the paper with Jitao Chen,
    formerly a postdoctoral scholar at UC Davis and now at the Nanjing
    Institute of Geology and Palaeontology, China and Xiang-dong Wang,
    Nanjing University, China.

    Additional coauthors are: Shuang Zhang, Texas A&M University; Terry
    Isson, Sofia Rauzi and Kierstin Daviau, University of Waikato, New
    Zealand; Le Yao, Yu-ping Qi and Yue Wang, Nanjing Institute of Geology
    and Palaeontology; Sophia Macarewich and Christopher Poulsen, University
    of Michigan, Ann Arbor; Noah Planavsky, Yale University; Feifei Zhang,
    Jun-xuan Fan and Shu-zhong Shen, Nanjing University; and Ariel Anbar,
    Arizona State University.

    The work was supported by the National Natural Science Foundation of
    China, the Chinese Academy of Sciences and the U.S. National Science Foundation.


    ========================================================================== Story Source: Materials provided by
    University_of_California_-_Davis. Original written by Andy Fell. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Jitao Chen, Isabel P. Montan~ez, Shuang Zhang, Terry T. Isson,
    Sophia I.

    Macarewich, Noah J. Planavsky, Feifei Zhang, Sofia Rauzi, Kierstin
    Daviau, Le Yao, Yu-ping Qi, Yue Wang, Jun-xuan Fan, Christopher J.

    Poulsen, Ariel D. Anbar, Shu-zhong Shen, Xiang-dong Wang. Marine
    anoxia linked to abrupt global warming during Earth's penultimate
    icehouse.

    Proceedings of the National Academy of Sciences, 2022; 119 (19)
    DOI: 10.1073/pnas.2115231119 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/05/220502170851.htm

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