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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
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The deep ocean circulation that forms around Antarctica could be headed
for collapse, say scientists.


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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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