Seasonal variability of the Arabian Sea intermediate circulation and its impact on seasonal changes of the upper oxygen minimum zone
<p>Oxygen minimum zones (OMZs) in the open ocean occur below the surface in regions of weak ventilation and high biological productivity with associated sinking organic matter. Very low levels of dissolved oxygen alter biogeochemical cycles and significantly affect marine life. One of the most...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | Ocean Science |
| Online Access: | https://os.copernicus.org/articles/16/1459/2020/os-16-1459-2020.pdf |
| Summary: | <p>Oxygen minimum zones (OMZs) in the open ocean occur below
the surface in regions of weak ventilation and high biological productivity
with associated sinking organic matter. Very low levels of dissolved oxygen
alter biogeochemical cycles and significantly affect marine life. One of the
most intense though poorly understood OMZs in the world ocean is located in
the Arabian Sea between 300 and 1000 m of depth. An improved understanding of
the physical processes that have an impact on the OMZ in the Arabian Sea is
expected to increase the reliability of assessments of its future
development.</p>
<p>This study uses reanalysis velocity fields from the ocean model HYCOM
(Hybrid Coordinate Ocean Model), which are verified with observational data,
to investigate advective pathways of Lagrangian particles into the Arabian
Sea OMZ at intermediate depths between 200 and 800 m.</p>
<p>In the eastern basin, the vertical expansion of the OMZ is strongest during
the winter monsoon, revealing a core thickness 1000 m deep and oxygen values
below 5 <span class="inline-formula">µ</span>mol <span class="inline-formula">kg<sup>−1</sup></span>. The minimum oxygen concentration might be favoured
by a maximum water mass advection that follows the main advective pathway of
Lagrangian particles along the perimeter of the basin into the eastern basin
of the Arabian Sea during the winter monsoon. These water masses pass regions of
high primary production and respiration, contributing to the transport of low-oxygenated water into the eastern part of the OMZ.</p>
<p>The maximum oxygen concentration in the western basin of the Arabian Sea
in May coincides with a maximum southward water mass advection in the
western basin during the spring intermonsoon, supplying the western core of the
OMZ with high-oxygenated water.</p>
<p>The maximum oxygen concentration in the eastern basin of the Arabian Sea
in May might be associated with the northward inflow of water across
10<span class="inline-formula"><sup>∘</sup></span> N into the Arabian Sea, which is highest during the spring
intermonsoon.</p>
<p>The Red Sea outflow of advective particles into the western and eastern
basin starts during the summer monsoon associated with the northeastward
current during the summer monsoon. On the other hand, waters from the Persian
Gulf are advected with little variation on seasonal timescales.</p>
<p>As the weak seasonal cycle of oxygen concentration in the eastern and
western basin can be explained by seasonally changing advection of water
masses at intermediate depths into the Arabian Sea OMZ (ASOMZ), the simplified backward-trajectory approach seems to be a good method for prediction of the
seasonality of advective pathways of Lagrangian particles into the ASOMZ.</p> |
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| ISSN: | 1812-0784 1812-0792 |