Climate change is making one of the world's strongest currents flow
faster

Date:
November 29, 2021
Source:
University of California - San Diego
Summary:
The Antarctic Circumpolar Current (ACC), the only ocean current
that circumnavigates the planet, is speeding up. For the first
time, scientists are able to tell that this is happening by taking
advantage of a decades-long set of observational records.



FULL STORY ==========================================================================
The Antarctic Circumpolar Current (ACC), the only ocean current
that circumnavigates the planet, is speeding up. For the first time,
scientists are able to tell that this is happening by taking advantage
of a decades-long set of observational records.


========================================================================== Researchers from Scripps Institution of Oceanography at UC San Diego,
Woods Hole Oceanographic Institution, the Chinese Academy of Sciences,
and UC Riverside used satellite measurements of sea-surface height and
data collected by the global network of ocean floats called Argo to
detect a trend in Southern Ocean upper layer velocity that had been
hidden to scientists until now.

The team representing the National Science Foundation-funded Southern
Ocean Carbon and Climate Observations and Modeling (SOCCOM) project
reports its findings in the Nov. 29 issue of the journal Nature Climate
Change.

Prevailing westerly winds have sped up as climate warms. Models show
that the wind speedup does not change the ocean currents much. Rather,
it energizes ocean eddies, which are circular movements of water running counter to main cuurents.

"From both observations and models, we find that the ocean heat change
is causing the significant ocean current acceleration detected during
recent decades," said Jia-Rui Shi, formerly a PhD student at Scripps Oceanography and currently a postdoctoral researcher at Woods Hole Oceanographic Institution.

"This speedup of the ACC, especially its jet centered on the Subantarctic Front, facilitates property exchange, such as of heat or carbon, between
ocean basins and creates the opportunity for these properties to increase
in subsurface subtropical regions." The ACC encircles Antarctica and
separates cold water in the south from warmer subtropical water just
to its north. This warmer part of the Southern Ocean takes up a lot of
the heat that human activities are adding to Earth's atmosphere. For
this reason, scientists consider it vital to understand its dynamics,
since what happens there could influence climate everywhere else.

The ocean warming pattern is important. When the gradient, or amount
of heat difference, between warm and cold waters increases, currents
between those two masses speed up.

"The ACC is mostly driven by wind, but we show that changes in its
speed are surprisingly mostly due to changes in the heat gradient," said co-author Lynne Talley, a physical oceanographer at Scripps Oceanography.

Long-term data capturing changes in the Southern Ocean were hard to
come by before the availability of satellite-mounted instruments and
the Argo network.

That network of autonomous floats, which measure ocean conditions such
as temperature and salinity, began in 1999 and reached full capacity
in 2007. A full complement of 4,000 floats across the world's oceans
continues to collect data to this day. The researchers were thus able to
use more than a decade's worth of comprehensive Argo data to distinguish
the trend of the accelerating current from natural variability.

Study co-authors said it is also likely that the speed of the current
will increase even more as the Southern Ocean continues to take up heat
from human- induced global warming.

Besides Shi and Talley, the research team included Scripps Oceanography
climate scientist Shang-Ping Xie, Qihua Peng of the Chinese Academy of Sciences, and Wei Liu of UC Riverside.

========================================================================== Story Source: Materials provided by
University_of_California_-_San_Diego. Original written by Robert
Monroe. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jia-Rui Shi, Lynne D. Talley, Shang-Ping Xie, Qihua Peng, Wei
Liu. Ocean
warming and accelerating Southern Ocean zonal flow. Nature Climate
Change, 2021; DOI: 10.1038/s41558-021-01212-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211129122815.htm

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