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Titel |
Intensification and deepening of the Arabian Sea Oxygen Minimum Zone in response to increase in Indian monsoon wind intensity |
VerfasserIn |
Zouhair Lachkar, Shafer Smith, Marina Lévy |
Konferenz |
EGU General Assembly 2017
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250138892
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Publikation (Nr.) |
EGU/EGU2017-2030.pdf |
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Zusammenfassung |
The decline in oxygen supply to the ocean associated with global warming of sea-surface
temperatures is expected to expand the oxygen minimum zones (OMZs). This global trend
can be attenuated or amplified by regional processes. In the Arabian Sea, the World’s thickest
OMZ is highly vulnerable to changes in the Indian monsoon wind. Evidence from
paleo records and future climate projections indicate strong variations of the Indian
monsoon wind intensity over climatic timescales. Yet, the response of the OMZ to
these wind changes remains poorly understood and its amplitude and timescale
unexplored. Here, we investigate the impacts of perturbations in Indian monsoon wind
intensity (from -50% to +50%) on the size and intensity of the Arabian Sea OMZ,
and examine the biogeochemical and ecological implications of these changes. To
this end, we conducted a series of eddy-resolving simulations of the Arabian Sea
using the Regional Oceanic Modeling System (ROMS) coupled to a nitrogen based
Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) ecosystem model that includes a
representation of the O2 cycle. We show that the Arabian Sea productivity increases and its
OMZ expands and deepens in response to monsoon wind intensification. These responses are
dominated by the perturbation of the summer monsoon wind, whereas the changes in the
winter monsoon wind play a secondary role. While the productivity responds quickly and
nearly linearly to wind increase (i.e., on a timescale of years), the OMZ response
is much slower (i.e., a timescale of decades). Our analysis reveals that the OMZ
expansion at depth is driven by increased oxygen biological consumption, whereas its
surface weakening is induced by increased lateral ventilation. The enhanced lateral
ventilation favors episodic intrusions of oxic waters in the lower epipelagic zone
(100-200m) of the western and central Arabian Sea, leading to intermittent expansions of
habitats and a more frequent alternation of hypoxic and oxic conditions there. The
increased productivity and deepening of the OMZ also lead to a strong intensification of
denitrification at depth, resulting in a substantial amplification of fixed nitrogen
depletion in the Arabian Sea. We conclude that changes in the Indian monsoon can
affect, on longer timescales, the large-scale biogeochemical cycles of nitrogen and
carbon, with a positive feedback on climate change in the case of stronger winds. |
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