MSGID: 1:317/3 6270b03d   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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