Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuary
<p>We examined the evolution of intermittent hypoxia off the Pearl River estuary based on three cruise legs conducted in July 2018: one during severe hypoxic conditions before the passage of a typhoon and two post-typhoon legs showing destruction of the hypoxia and its reinstatement. The lowes...
Main Authors: | , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2021-04-01
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Series: | Biogeosciences |
Online Access: | https://bg.copernicus.org/articles/18/2755/2021/bg-18-2755-2021.pdf |
Summary: | <p>We examined the evolution of intermittent hypoxia off the
Pearl River estuary based on three cruise legs conducted in July 2018: one
during severe hypoxic conditions before the passage of a typhoon and two
post-typhoon legs showing destruction of the hypoxia and its reinstatement.
The lowest ever recorded regional dissolved oxygen (DO) concentration of 3.5 <span class="inline-formula">µ</span>mol kg<span class="inline-formula"><sup>−1</sup></span> (<span class="inline-formula">∼</span> 0.1 mg L<span class="inline-formula"><sup>−1</sup></span>) was observed in bottom
waters during leg 1, with an <span class="inline-formula">∼</span> 660 km<span class="inline-formula"><sup>2</sup></span> area experiencing
hypoxic conditions (DO <span class="inline-formula"><i><</i></span> 63 <span class="inline-formula">µ</span>mol kg<span class="inline-formula"><sup>−1</sup></span>). Hypoxia was
completely destroyed by the typhoon passage but was quickly restored
<span class="inline-formula">∼</span> 6 d later, resulting primarily from high biochemical
oxygen consumption in bottom waters that averaged 14.6 <span class="inline-formula">±</span> 4.8 <span class="inline-formula">µ</span>mol O<span class="inline-formula"><sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span> d<span class="inline-formula"><sup>−1</sup></span>. The shoreward intrusion of offshore subsurface
waters contributed to an additional 8.6 <span class="inline-formula">±</span> 1.7 % of oxygen loss
during the reinstatement of hypoxia. Freshwater inputs suppressed
wind-driven turbulent mixing, stabilizing the water column and facilitating
the hypoxia formation. The rapid reinstatement of summer hypoxia has a
shorter timescale than the water residence time, which is however comparable
with that of its initial disturbance from frequent tropical cyclones that
occur throughout the wet season. This has important implications for
better understanding the intermittent nature of hypoxia and predicting
coastal hypoxia in a changing climate.</p> |
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ISSN: | 1726-4170 1726-4189 |