Subpolar marginal seas play a key role in making the subarctic Pacific nutrient-rich

Date:
August 7, 2020
Source:
Hokkaido University
Summary:
A group of researchers has discovered why the western subarctic
Pacific Ocean, which accounts for only 6 percent of the world's
oceans, produces an estimated 26 percent of the world's marine
resources.



FULL STORY ==========================================================================
A group of researchers from three Japanese universities has discovered why
the western subarctic Pacific Ocean, which accounts for only 6 percent
of the world's oceans, produces an estimated 26 percent of the world's
marine resources.


========================================================================== Japan neighbors this ocean area, known for rich marine resources including salmon and trout. The area, located at the termination of the global
ocean circulation called the ocean conveyor belt, has one of the largest biological carbon dioxide draw-downs of the world's oceans.

The study, led by Hokkaido University, the University of Tokyo and
Nagasaki University, showed that water rich in nitrate, phosphate
and silicate - - essential chemicals for producing phytoplankton --
is pooled in the intermediate water (from several hundred meters to a
thousand meters deep) in the western subarctic area, especially in the
Bering Sea basin. Nutrients are uplifted from the deep ocean through the intermediate water to the surface, and then return to the intermediate
nutrient pool as sinking particles through the biological production
and microbial degradation of organic substances.

The intermediate water mixes with dissolved iron that originates in the
Okhotsk Sea and is uplifted to the surface -- pivotal processes linking
the intermediate water and the surface and that maintain high surface biological productivity. This finding defies the conventional view that nutrients are simply uplifted from the deep ocean to the surface.

The study relied on ocean data obtained by a research vessel that
surveyed the marginal seas (the Okhotsk Sea and the Bering Sea) where,
the group believed, large-scale mixture of seawater occurs due to the interaction of tidal currents with the rough topography. This voyage was
made in collaboration with a Russian research team because many of the
areas surveyed fall inside Russia's exclusive economic zone. The obtained
data was then combined with data collected by Japanese research vessels.

Analysis of the data showed that nitrate and phosphate re-produced
through microbial degradation of organic substances accumulate in high concentrations in intermediate water in the entire subpolar Pacific
region.

The researchers also found that the vertical mixing magnitude near the
Kuril Islands and the Aleutian Islands is far stronger than that in the surrounding open seas. This study demonstrated that large-scale vertical
mixing in the marginal seas breaks the density stratification to mix ocean water, transporting nutrients from the intermediate water to the surface.

"Our findings should help deepen understanding about the circulation of
carbon and nutrients in the ocean and ecological changes caused by climate change," says Associate Professor Jun Nishioka of Hokkaido University,
who led the study.


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


========================================================================== Journal Reference:
1. Jun Nishioka, Hajime Obata, Hiroshi Ogawa, Kazuya Ono, Youhei
Yamashita,
Keunjong Lee, Shigenobu Takeda, Ichiro Yasuda. Subpolar marginal
seas fuel the North Pacific through the intermediate water at
the termination of the global ocean circulation. Proceedings
of the National Academy of Sciences, 2020; 117 (23): 12665 DOI:
10.1073/pnas.2000658117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200807102330.htm

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