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Mid-Holocene intensification of the oxygen minimum zone in the northeastern Arabian Sea

Abstract. 

"The Arabian Sea is characterized by a strong Oxygen Minimum Zone (OMZ) bearing sub-oxic conditions at the intermediate water depth. We analyzed a sediment core near the upper margin of OMZ (174 m water depth) from offshore Saurashtra, northeastern (NE) Arabian Sea to reconstruct multi-proxy biogeochemical response in the area during the Early-Middle Holocene (∼10–4 ka before present). The results indicate lower foraminiferal productivity (both benthic and planktic) and weak sub-surface denitrification causing mild OMZ conditions at the study site during the early Holocene (∼10–8 ka). Subsequently, an increased foraminiferal productivity and sub-surface (both the water column and sediment) denitrification in the area led to intensified OMZ conditions during the mid-Holocene (after ∼8 ka). [...]".

 

Source: Science Direct

Authors: Syed Azharuddin et al. 

DOI: https://doi.org/10.1016/j.jseaes.2022.105094

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Observed denitrification in the northeast Arabian Sea during the winter-spring transition of 2009

Abstract. 

"The central and northeast Arabian Sea (AS) has an intense and thick oxygen minimum zone (OMZ) and denitrification zone. It is comparable with the strongest OMZ of the north-equatorial Pacific Ocean. Denitrification in the AS is revisited using a set of cruise observations collected during February–March of 2009 by the Centre for Marine Living Resources, India. The region possesses one of the most robust N* depleted water reaching as low as -20 μmol l−1 at depths (~600 m). In AS, the oxygen depletion is mainly due to sluggish circulation, weak lateral and vertical ventilation. The biological respiration in oxygen deficit condition depletes nitrate and further modifies the Redfield ratio at intermediate depths (200-600 m) from 16N:1P to 8N:1P. [...]".

 

Source: Science Direct

Authors: Anju Mallissery et al.

DOI: https://doi.org/10.1016/j.jmarsys.2021.103680

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Oxygen minimum zone along the eastern Arabian Sea: Intra-annual variation and dynamics based on ship-borne studies

Abstract.

"The oxygen minimum zone (OMZ) in the eastern Arabian Sea (EAS, ∼6° to 21°N), within Indian Exclusive Economic Zone (EEZ), is mapped, for the first time, for one year through ten repeated ship-based observations between December 2017 and January 2019 at seven to ten stations along the 2000 m depth contour. On an annual basis, the OMZ (<20 µM oxygen) in the EAS varied between 60 and 1350 m; its thickness decreased from north to south. During the winter monsoon, the upper boundary of the OMZ in the north and south was deeper (150–160 m) than the central EAS (∼110 m). [...]".

 

Source: Science Direct

Authors: Sudheesh Valliyodan et al.

DOI: https://doi.org/10.1016/j.pocean.2022.102742

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Variability of dissolved oxygen in the Arabian Sea Oxygen Minimum Zone and its driving mechanisms

Abstract.

"The Arabian Sea hosts one of the most intense, perennial Oxygen Minimum Zones (OMZ) in the world ocean. Observations along a meridional transect at 68°E extending from 8 to 21°N showed large seasonal as well as interannual changes in the dissolved oxygen and nitrite concentrations. Unlike previous studies that used observations from the periphery of the OMZ, our observations are from its core and also allow us demarcating the southern extent of the OMZ. [...]"

Source: Journal of Marine Systems
Authors: Damodar M.Shenoy et al.
DOI: 10.1016/j.jmarsys.2020.103310 

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Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

Abstract.

"In response to rising CO2 concentrations and increasing global sea surface temperatures, oxygen minimum zones (OMZ), or “dead zones”, are expected to expand. OMZs are fueled by high primary productivity, resulting in enhanced biological oxygen demand at depth, subsequent oxygen depletion, and attenuation of remineralization. This results in the deposition of organic carbon‐rich sediments. Carbon drawdown is estimated by biogeochemical models; however, a major process is ignored: carbon fixation in the mid‐ and lower water column. [...]"

Source: Global Biogeochemical Cycles
Authors: Sabine K. Lengger et al.
DOI: 10.1029/2019GB006282

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High-throughput screening of sediment bacterial communities from Oxygen Minimum Zones of the northern Indian Ocean

Abstract.

"The Northern Indian Ocean host two recognized Oxygen Minimum Zones (OMZ): one in the Arabian Sea and the other in the Bay of Bengal region. The next-generation sequencing technique was used to understand the total bacterial diversity from the surface sediment of off Goa within the OMZ of Arabian Sea, and from off Paradip within the OMZ of Bay of Bengal. [...]"

Source: Biogeosciences (preprint)
Authors: Jovitha Lincy and Cathrine Manohar
DOI: 10.5194/bg-2019-330

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Microbial diversity of the Arabian Sea in the Oxygen minimum zones by metagenomics approach

Abstract.

"Large oxygen depleted areas known as oxygen minimum zones (OMZ) have been observed in the Arabian Sea and recent reports indicate that these areas are expanding at an alarming rate. In marine waters, oxygen depletion may also be related to global warming and the temperature rise, acidification and deoxygenation can lead to major consequences wherein the plants, fish and other biota will struggle to survive in the ecosystem. [...]"

Source: bioRxiv
Authors: Mandar S Paingankar et al.
DOI: 10.1101/731828

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Strong intensification of the Arabian Sea oxygen minimum zone in response to Arabian Gulf warming

Abstract.

"The highly saline, oxygen saturated waters of the Arabian Gulf (hereafter the Gulf) sink to intermediate depths (200‐300m) when they enter the Arabian Sea, ventilating the World's thickest oxygen minimum zone (OMZ). Here, we investigate the impacts of a warming of the Gulf consistent with climate change projections on the intensity of this OMZ. Using a series of eddy‐resolving model simulations, we show that the warming of the Gulf waters increases their buoyancy and hence limits their contribution to the ventilation of intermediate depths. [...]"

Source: Geophysical Research Letters
Authors: Z. Lachkar, M. Lévy and S. Smith
DOI: 10.1029/2018GL081631

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Assessment of the impact of spatial resolution on ROMS simulated upper-ocean biogeochemistry of the Arabian Sea from an operational perspective

Abstract.

"The resolution of the model emerges to be an important factor in simulating the real oceanic features. In this paper, the performance of two coupled bio-physical models, having spatial resolutions 1/12° (∼9 km) and 1/4° (∼25 km) configured using Regional Ocean Modeling System (ROMS), have been evaluated in simulating upper ocean dynamics of the Arabian Sea. [...]"

Source: Journal of Operational Oceanography
Authors: Kunal Chakraborty et al.
DOI: 10.1080/1755876X.2019.1588697

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Autonomous profiling float observations reveal the dynamics of deep biomass distributions in the denitrifying oxygen minimum zone of the Arabian Sea

Abstract.

"Data from 13 autonomous profiling BGC-Argo floats, equipped with biogeochemical and bio-optical sensors deployed between 2011 and 2016, were used to explore the potential of bio-optical methods to map deep biomass distribution in the Arabian Sea oxygen minimum zone (OMZ). Dissolved oxygen sensors revealed concentrations below 5 μmol kg−1 for much of the depth range between 200 and 400 m and below 1 μmol kg−1 in the centre of the OMZ, which is well below climatological values. [...]"

Source: Journal of Marine Systems
Authors: Bożena Wojtasiewicz et al.
DOI: 10.1016/j.jmarsys.2018.07.002

Read the full article here.


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