• Climate change has likely begun to suffo

    From ScienceDaily@1:317/3 to All on Tue Feb 1 21:30:42 2022
    Climate change has likely begun to suffocate the world's fisheries


    Date:
    February 1, 2022
    Source:
    American Geophysical Union
    Summary:
    By 2080, around 70% of the world's oceans could be suffocating
    from a lack of oxygen as a result of climate change, potentially
    impacting marine ecosystems worldwide, according to a new
    study. The new models find mid-ocean depths that support many
    fisheries worldwide are already losing oxygen at unnatural rates
    and passed a critical threshold of oxygen loss in 2021.



    FULL STORY ==========================================================================
    By 2080, around 70% of the world's oceans could be suffocating from
    a lack of oxygen as a result of climate change, potentially impacting
    marine ecosystems worldwide, according to a new study. The new models
    find mid-ocean depths that support many fisheries worldwide are already
    losing oxygen at unnatural rates and passed a critical threshold of
    oxygen loss in 2021.


    ========================================================================== Oceans carry dissolved oxygen as a gas, and just like land animals,
    aquatic animals need that oxygen to breathe. But as the oceans warm due
    to climate change, their water can hold less oxygen. Scientists have been tracking the oceans' steady decline in oxygen for years, but the new study provides new, pressing reasons to be concerned sooner rather than later.

    The new study is the first to use climate models to predict how and
    when deoxygenation, which is the reduction of dissolved oxygen content
    in water, will occur throughout the world's oceans outside its natural variability.

    It finds that significant, potentially irreversible deoxygenation of the ocean's middle depths that support much of the world's fished species
    began occurring in 2021, likely affecting fisheries worldwide. The new
    models predict that deoxygenation is expected to begin affecting all
    zones of the ocean by 2080.

    The results were published in the AGU journal Geophysical Research
    Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

    The ocean's middle depths (from about 200 to 1,000 meters deep), called mesopelagic zones, will be the first zones to lose significant amounts
    of oxygen due to climate change, the new study finds. Globally, the
    mesopelagic zone is home to many of the world's commercially fished
    species, making the new finding a potential harbinger of economic
    hardship, seafood shortages and environmental disruption.



    ========================================================================== Rising temperatures lead to warmer waters that can hold less
    dissolved oxygen, which creates less circulation between the ocean's
    layers. The middle layer of the ocean is particularly vulnerable to deoxygenation because it is not enriched with oxygen by the atmosphere
    and photosynthesis like the top layer, and the most decomposition of
    algae -- a process that consumes oxygen -- occurs in this layer.

    "This zone is actually very important to us because a lot of commercial
    fish live in this zone," says Yuntao Zhou, an oceanographer at Shanghai
    Jiao Tong University and lead study author. "Deoxygenation affects
    other marine resources as well, but fisheries [are] maybe most related
    to our daily life." The new findings are deeply concerning and adds to
    the urgency to engage meaningfully in mitigating climate change, says
    Matthew Long, an oceanographer at NCAR who was not involved in the study.

    "Humanity is currently changing the metabolic state of the largest
    ecosystem on the planet, with really unknown consequences for marine ecosystems," he said.

    "That may manifest in significant impacts on the ocean's ability to
    sustain important fisheries." Evaluating vulnerability The researchers identified the beginning of the deoxygenation process in three ocean
    depth zones -- shallow, middle and deep -- by modeling when the loss of
    oxygen from the water exceeds natural fluctuations in oxygen levels. The
    study predicted when deoxygenation would occur in global ocean basins
    using data from two climate model simulations: one representing a high emissions scenario and the other representing a low emissions scenario.

    In both simulations, the mesopelagic zone lost oxygen at the fastest
    rate and across the largest area of the global oceans, although the
    process begins about 20 years later in the low emissions scenario. This indicates that lowering carbon dioxide and other greenhouse gas emissions
    could help delay the degradation of global marine environments.

    The researchers also found that oceans closer to the poles, like the west
    and north Pacific and the southern oceans, are particularly vulnerable
    to deoxygenation. They're not yet sure why, although accelerated warming
    could be the culprit. Areas in the tropics known for having low levels of dissolved oxygen, called oxygen minimum zones, also seem to be spreading, according to Zhou.

    "The oxygen minimum zones actually are spreading into high latitude
    areas, both to the north and the south. That's something we need to pay
    more attention to," she says. Even if global warming were to reverse,
    allowing concentrations of dissolved oxygen to increase, "whether
    dissolved oxygen would return to pre- industrial levels remains unknown." special promotion Explore the latest scientific research on sleep and
    dreams in this free online course from New Scientist -- Sign_up_now_>>> ========================================================================== Story Source: Materials provided by American_Geophysical_Union. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Hongjing Gong, Chao Li, Yuntao Zhou. Emerging Global Ocean
    Deoxygenation
    Across the 21st Century. Geophysical Research Letters, 2021; 48
    (23) DOI: 10.1029/2021GL095370 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/02/220201161050.htm

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