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Fast local warming is the main driver of recent deoxygenation in the northern Arabian Sea.
- Source :
- Biogeosciences; 2021, Vol. 18 Issue 20, p5831-5849, 19p
- Publication Year :
- 2021
-
Abstract
- The Arabian Sea (AS) hosts one of the most intense oxygen minimum zones (OMZs) in the world. Observations suggest a decline in O 2 in the northern AS over the recent decades accompanied by an intensification of the suboxic conditions there. Over the same period, the local sea surface temperature has risen significantly, particularly over the Arabian Gulf (also known as Persian Gulf, hereafter the Gulf), while summer monsoon winds may have intensified. Here, we simulate the evolution of dissolved oxygen in the AS from 1982 through 2010 and explore its controlling factors, with a focus on changing atmospheric conditions. To this end, we use a set of eddy-resolving hindcast simulations forced with winds and heat and freshwater fluxes from an atmospheric reanalysis. We find a significant deoxygenation in the northern AS, with O 2 inventories north of 20 ∘ N dropping by over 6 % per decade between 100 and 1000 m. These changes cause an expansion of the OMZ volume north of 20 ∘ N at a rate of 0.6 % per decade as well as an increase in the volume of suboxia and the rate of denitrification by 14 and 15 % per decade, respectively. We also show that strong interannual and decadal variability modulate dissolved oxygen in the northern AS, with most of the O 2 decline taking place in the 1980s and 1990s. Using a set of sensitivity simulations we demonstrate that deoxygenation in the northern AS is essentially caused by reduced ventilation induced by the recent fast warming of the sea surface, including in the Gulf, with a contribution from concomitant summer monsoon wind intensification. This is because, on the one hand, surface warming enhances vertical stratification and increases Gulf water buoyancy, thus inhibiting vertical mixing and ventilation of the thermocline. On the other hand, summer monsoon wind intensification causes a rise in the thermocline depth in the northern AS that lowers O 2 levels in the upper ocean. Our findings confirm that the AS OMZ is strongly sensitive to upper-ocean warming and concurrent changes in the Indian monsoon winds. Finally, our results also demonstrate that changes in the local climatic forcing play a key role in regional dissolved oxygen changes and hence need to be properly represented in global models to reduce uncertainties in future projections of deoxygenation. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 17264170
- Volume :
- 18
- Issue :
- 20
- Database :
- Complementary Index
- Journal :
- Biogeosciences
- Publication Type :
- Academic Journal
- Accession number :
- 153442446
- Full Text :
- https://doi.org/10.5194/bg-18-5831-2021