MSGID: 1:317/3 642661fa   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Deep ocean currents around Antarctica headed for collapse, study finds   
      
      
     Date:   
         March 30, 2023   
     Source:   
         University of New South Wales   
     Summary:   
         Antarctic circulation could slow by more than 40 per cent over the   
         next three decades, with significant implications for the oceans   
         and the climate.   
      
      
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   FULL STORY   
   ==========================================================================   
   The deep ocean circulation that forms around Antarctica could be headed   
   for collapse, say scientists.   
      
      
   ==========================================================================   
   Such decline of this ocean circulation will stagnate the bottom of   
   the oceans and generate further impacts affecting climate and marine   
   ecosystems for centuries to come.   
      
   The results are detailed in a new study coordinated by Scientia Professor   
   Matthew England, Deputy Director of the ARC Centre for Excellence in   
   Antarctic Science (ACEAS) at UNSW Sydney. The work, published today   
   in Nature, includes lead author Dr. Qian Li -- formerly from UNSW and   
   now at the Massachusetts Institute of Technology (MIT) -- as well as   
   co-authors from the Australian National University (ANU) and CSIRO.   
      
   Cold water that sinks near Antarctica drives the deepest flow of the   
   overturning circulation -- a network of currents that spans the world's   
   oceans.   
      
   The overturning carries heat, carbon, oxygen and nutrients around   
   the globe.   
      
   This influences climate, sea level and the productivity of marine   
   ecosystems.   
      
   "Our modelling shows that if global carbon emissions continue at the   
   current rate, then the Antarctic overturning will slow by more than 40   
   per cent in the next 30 years -- and on a trajectory that looks headed   
   towards collapse," says Prof England.   
      
   Modelling the deep ocean About 250 trillion tonnes of cold, salty,   
   oxygen-rich water sinks near Antarctica each year. This water then   
   spreads northwards and carries oxygen into the deep Indian, Pacific and   
   Atlantic Oceans.   
      
   "If the oceans had lungs, this would be one of them," Prof England says.   
      
   The international team of scientists modelled the amount of Antarctic   
   deep water produced under the IPCC 'high emissions scenario', until 2050.   
      
   The model captures detail of the ocean processes that previous models   
   haven't been able to, including how predictions for meltwater from ice   
   might influence the circulation.   
      
   This deep ocean current has remained in a relatively stable state   
   for thousands of years, but with increasing greenhouse gas emissions,   
   Antarctic overturning is predicted to slow down significantly over the   
   next few decades.   
      
   Impacts of reduced Antarctic overturning With a collapse of this deep   
   ocean current, the oceans below 4000 metres would stagnate.   
      
   "This would trap nutrients in the deep ocean, reducing the nutrients   
   available to support marine life near the ocean surface," says Prof   
   England.   
      
   Co-author Dr Steve Rintoul of CSIRO and the Australian Antarctic Program   
   Partnership says the model simulations show a slowing of the overturning,   
   which then leads to rapid warming of the deep ocean.   
      
   "Direct measurements confirm that warming of the deep ocean is indeed   
   already underway," says Dr Rintoul. The study found melting ice around   
   Antarctica makes the nearby ocean waters less dense, which slows the   
   Antarctic overturning circulation. The melt of the Antarctic and Greenland   
   ice sheets is expected to continue to accelerate as the planet warms.   
      
   "Our study shows that the melting of the ice sheets has a dramatic   
   impact on the overturning circulation that regulates Earth's climate,"   
   says Dr Adele Morrison, also from ACEAS and the ANU Research School of   
   Earth Sciences.   
      
   "We are talking about the possible long-term extinction of an iconic   
   water mass," says Prof England.   
      
   "Such profound changes to the ocean's overturning of heat, freshwater,   
   oxygen, carbon and nutrients will have a significant adverse impact on   
   the oceans for centuries to come."   
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Global_Warming # Oceanography # Climate # Geography   
             o Fossils_&_Ruins   
                   # Early_Climate # Origin_of_Life # Fossils # Ancient_DNA   
       * RELATED_TERMS   
             o Global_climate_model o Climate o Greenland_ice_sheet o   
             Climate_model o Antarctic_krill o Global_warming o Deforestation   
             o Antarctic_Circle   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_New_South_Wales. Original written by Melissa Lyne. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Qian Li, Matthew H. England, Andrew McC. Hogg, Stephen R. Rintoul,   
      Adele   
         K. Morrison. Abyssal ocean overturning slowdown and warming   
         driven by Antarctic meltwater. Nature, 2023; 615 (7954): 841 DOI:   
         10.1038/s41586- 023-05762-w   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230330102327.htm   
      
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