MSGID: 1:317/3 649d08f1   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    There may be good news about the oceans in a globally warmed world   
    Study suggests ongoing oxygen loss from the seas due to climate change   
   may reverse in the future    
      
     Date:   
         June 28, 2023   
     Source:   
         Rutgers University   
     Summary:   
         An analysis of oxygen levels in Earth's oceans may provide some   
         rare, good news about the health of the seas in a future, globally   
         warmed world. A study analyzing ocean sediment shows that ocean   
         oxygen levels in a key area were higher during the Miocene warm   
         period, some 16 million years ago when the Earth's temperature   
         was hotter than it is today.   
      
      
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   FULL STORY   
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   An analysis of oxygen levels in Earth's oceans may provide some rare,   
   good news about the health of the seas in a future, globally warmed world.   
      
   A Rutgers-led study published in Nature analyzing ocean sediment shows   
   that ocean oxygen levels in a key area were higher during the Miocene   
   warm period, some 16 million years ago when the Earth's temperature was   
   hotter than it is today.   
      
   In recent decades, levels of life-sustaining oxygen in the ocean have   
   been decreasing, raising concerns that oxygen-deficient zones in key   
   parts of the world oceans will expand, further harming marine life.   
      
   Scientists have attributed the trend to climate change-induced rising   
   temperatures, which affect the amount of oxygen that can be absorbed   
   from the atmosphere.   
      
   "Our study shows that the eastern equatorial Pacific, which today is home   
   to the largest oxygen-deficient zone in the oceans, was well oxygenated   
   during the Miocene warm period, despite the fact that global temperatures   
   at that time were higher than at present," said Anya Hess, the lead author   
   of the study and a Rutgers doctoral student working with Yair Rosenthal,   
   a Distinguished Professor focused on marine and Earth sciences with the   
   Rutgers School of Art and Sciences and the School of Environmental and   
   Biological Sciences.   
      
   Hess added: "This suggests that current oxygen loss may ultimately   
   reverse."  The fastest rates of oxygen loss in recent decades have   
   been in oxygen- deficient zones, and they are expected to continue to   
   expand and become shallower, threatening fisheries by shrinking fish   
   habitat. However, climate models diverge in their predictions of how   
   these zones will respond beyond the year 2100, inspiring the team to   
   investigate more.   
      
   To test current climate models, researchers chose the mid-Miocene,   
   when climate conditions were similar to those predicted for the next few   
   centuries in the current era of climate change. Researchers examined ocean   
   sediments deposited during the mid-Miocene in the eastern equatorial   
   Pacific. The sediments were recovered from the seafloor by scientists   
   aboard the National Science Foundation-funded research vessel JOIDES   
   Resolution as part of what is now known as the International Ocean   
   Discovery Program (IODP).   
      
   The researchers isolated the fossilized remains of microorganisms the   
   size of individual grains of sand that live in the water column called   
   foraminifera.   
      
   The scientists analyzed the chemical composition of the foraminifera,   
   which reflects the chemical profile of the ancient ocean. They discerned   
   oxygen levels of ancient oceans in a few ways, including using isotopes of   
   nitrogen - - forms of the element that have a different relative atomic   
   mass -- as detectors. The isotopes are sensitive to a process called   
   denitrification that only occurs at very low oxygen levels. They also   
   employed a method of analysis that compares levels of iodine and calcium   
   and gives subtle readings that can differentiate between well-oxygenated   
   conditions and moderately well-oxygenated conditions.   
      
   The methods showed the area was well oxygenated during the height of   
   Miocene warmth, even approaching modern day levels seen in the open-ocean   
   South Pacific.   
      
   "These results were unexpected and suggest that the solubility-driven   
   loss of oxygen that has occurred in recent decades is not the end of   
   the story for oxygen's response to climate change," Rosenthal said.   
      
   Other authors on the study include Ken Miller, a Distinguished Professor   
   in the Department of Earth and Planetary Sciences in the Rutgers School   
   of Arts and Sciences, Alexandra Auderset and Alfredo Martinez-Garcia   
   of the Max Planck Institute for Chemistry in Germany, Daniel Sigman of   
   Princeton University and Xiaoli Zhou of Tongji University in China.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Environmental_Awareness # Climate # Oceanography #   
                   Global_Warming   
             o Fossils_&_Ruins   
                   # Early_Climate # Origin_of_Life # Fossils # Early_Mammals   
       * RELATED_TERMS   
             o Ocean o Ocean_current o Ozone o Paleoclimatology o   
             Antarctic_ice_sheet o Greenland_ice_sheet o Climate_model   
             o Oxygen   
      
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   Story Source: Materials provided by Rutgers_University. Original written   
   by Kitta MacPherson.   
      
   Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Anya V. Hess, Alexandra Auderset, Yair Rosenthal, Kenneth G. Miller,   
         Xiaoli Zhou, Daniel M. Sigman, Alfredo Marti'nez-Garci'a. A well-   
         oxygenated eastern tropical Pacific during the warm Miocene. Nature,   
         2023; DOI: 10.1038/s41586-023-06104-6   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230628125214.htm   
      
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