Eddies: Circular currents and their influence on the world's hottest
ocean

Date:
June 9, 2023
Source:
Tohoku University
Summary:
Water from the Pacific Ocean flows into the Indian Ocean via the
Indonesia Archipelago thanks to a vast network of currents that act
as a conveyor belt, transporting warmth and nutrients. Currents can
sometimes form circular motions and these are known as eddies. An
international group of researchers has modeled the impacts of
eddies on the currents that carry water from the Pacific Ocean to
the Indian Ocean.


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==========================================================================
FULL STORY ========================================================================== Water from the Pacific Ocean flows into the Indian Ocean via the
Indonesia Archipelago Seas thanks to a vast network of currents dubbed the Indonesian Throughflow (ITF). The ITF acts as a heat and moisture conveyer belt, transporting warm and nutrient waters. Yet the ITF is neither a
steady nor a straight path, but experiences fluctuations and turbulence
as it passes through the various sea regions, straits, and passages.

Currents can sometimes formulate into circular motions, forming a
whirlpool- like phenomena. These are known as eddies, and they are
prominent in areas where there are strong gradients in temperature,
salinity, or velocity. Their rotating motion can cause nutrients from
the colder, deeper waters to rise to the surface.

To investigate the role eddies play in determining the path of the ITF,
an international research group has harnessed a high-resolution ocean
general circulation model that reproduces eddies. The group featured researchers from Tohoku University, JAMSTEC, Kyushu University, the
University of Hawai`i at Manoa, and the National Research and Innovation
Agency of Indonesia.

Details of their research were reported in the Journal of Geophysical
Research -- Oceans on May 14, 2023.

The group's model enabled them to calculate the transport of
simulated particles in a daily-averaged flow field with eddies and a monthly-averaged flow field with smoothed eddy currents, respectively,
and estimate the flow rate transported by the simulated particles.

In the Sulawesi Sea, which is situated along the northeastern coast
of Borneo and also borders the southern Filipino island of Mindanao,
the Sulu archipelago, and Sulawesi Island's western coast, the group
found that large flow fluctuations occur, and seawater circulates over a
wider area for an extended period. Seawater also rises from the middle
to near the surface, which may cause significant changes in the water
when flowing through due to turbulent mixing.

On the eastern side of Sulawesi Island sits the Banda Sea, which surrounds
the Maluku Islands and borders the islands of New Guinea and Timor. Here,
the current fluctuation is slight, and the model predicted negligible
influence from the eddies on the Indonesian Current.

"Our results indicate that the path and residence time of the ITF, along
with the mixing process of seawater, must be appropriately reproduced
by an ocean general circulation model to gain further insights into
and better predict sea surface temperature fluctuations in each region
of the Indonesian Archipelago," points out Toshio Suga, professor of
physical oceanography at Tohoku University's Graduate School of Science
and co-author of the paper.

Global warming's progression is expected to change the ITF. Such changes
could have profound repercussions for water temperatures in the Indonesia Archipelago and the Indian Ocean, El Nin~o and the Indian Ocean Dipole,
and the frequency and scale of marine heatwaves that affect marine
ecosystems and local weather.

Therefore, it is vital to predict accurately such phenomena.

Looking ahead, the group hopes to improve the accuracy of future
predictions by clarifying the degree to which eddies impact the path
and residence time of the ITF, something quantitatively linked to the determination of water temperature in these areas.

* RELATED_TOPICS
o Earth_&_Climate
# Oceanography # Water # Global_Warming # Geography #
Climate # Weather # Ecosystems # Ecology
* RELATED_TERMS
o Ocean_current o Ocean o El_Nin~o-Southern_Oscillation o
Mid-ocean_ridge o 1997_Pacific_typhoon_season o Climate o
Ocean_surface_wave o List_of_Category_5_Pacific_hurricanes

========================================================================== Story Source: Materials provided by Tohoku_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Mochamad Riza Iskandar, Yanli Jia, Hideharu Sasaki, Ryo Furue,
Shinichiro
Kida, Toshio Suga, Kelvin J. Richards. Effects of
High‐Frequency Flow Variability on the Pathways of the
Indonesian Throughflow. Journal of Geophysical Research: Oceans,
2023; 128 (5) DOI: 10.1029/2022JC019610 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230609125656.htm

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