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Expanding 'dead zone' in Arabian Sea raises climate change fears

In the waters of the Arabian Sea, a vast "dead zone" the size of Scotland is expanding and scientists say climate change may be to blame. In his lab in Abu Dhabi, Zouhair Lachkar is labouring over a colourful computer model of the Gulf of Oman, showing changing temperatures, sea levels and oxygen concentrations.His models and new research unveiled earlier this year show a worrying trend.Dead zones are areas of the sea where the lack of oxygen makes it difficult for fish to survive and the one in the Arabian Sea is "is the most intense in the world," says Lachkar, a senior scientist at NYU Abu Dhabi in the capital of the United Arab Emirates.

Source: phys.org

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Ventilation of oxygen to oxygen minimum zone due to anticyclonic eddies in the Bay of Bengal

Abstract.

"Intense oxygen minimum zone (OMZ) occurs in the mid‐depth of the Eastern Tropical Pacific (ETP), Arabian Sea (AS), and Bay of Bengal (BoB). However, the occurrence of anammox/denitrification was reported only in the ETP and AS and its absence in the BoB is attributed to presence of traces of dissolved oxygen (DO). Anticyclonic Eddies (ACE) supply high nutrient, organic‐rich and oxygen poor waters from the coastal upwelling regions leading to strengthening of OMZ in the offshore of AS and ETP.  [...]"

Source: Biogeosciences
Authors: V. V. S. S. Sarma, T. V. S. Udaya Bhaskar
DOI: 10.1029/2018JG004447

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Enhanced carbon-sulfur cycling in the sediments of Arabian Sea oxygen minimum zone center

Abstract.

"Biogeochemistry of oxygen minimum zone (OMZ) sediments, which are characterized by high input of labile organic matter, have crucial bearings on the benthic biota, gas and metal fluxes across the sediment-water interface, and carbon-sulfur cycling. Here we couple pore-fluid chemistry and comprehensive microbial diversity data to reveal the sedimentary carbon-sulfur cycle across a water-depth transect covering the entire thickness of eastern Arabian Sea OMZ, off the west coast of India. [...]"

Source: Scientific Reports
Authors: Svetlana Fernandes et al.
DOI: 10.1038/s41598-018-27002-2

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Physical controls on oxygen distribution and denitrification potential in the north west Arabian Sea

Abstract.

"At suboxic oxygen concentrations, key biogeochemical cycles change and denitrification becomes the dominant remineralization pathway. Earth system models predict oxygen loss across most ocean basins in the next century; oxygen minimum zones near suboxia may become suboxic and therefore denitrifying. Using an ocean glider survey and historical data, we show oxygen loss in the Gulf of Oman (from 6‐12 to < 2 μmol kg‐1) not represented in climatologies. [...]"

Source: Grophysical Research Letters
Authors: B. Y. Queste et al.
DOI: 10.1029/2017GL076666

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Growing 'dead zone' confirmed by underwater robots in the Gulf of Oman

"New research reveals a growing 'dead zone' in the Gulf of Oman. Little data has been collected in the area for almost 50 years because of piracy and geopolitical tensions. The area devoid of oxygen was confirmed by underwater robots. Reasearchers found an area larger than Scotland with almost no oxygen left. The environmental disaster is worse than expected with dire consequences for fish and marine plants, plus humans who rely on the oceans for food and employment. "

Source: Science Daily

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High total organic carbon in surface waters of the northern Arabian Gulf: Implications for the oxygen minimum zone of the Arabian Sea

Abstract.

"Measurements of total organic carbon (TOC) for two years in Kuwaiti waters showed high TOC levels (101.0–318.4, mean 161.2 μM) with maximal concentrations occurring within the polluted Kuwait Bay and decreasing offshore, indicating substantial anthropogenic component. Analysis of winter-time data revealed a large increase in density over the past four decades due to decrease in Shatt Al-Arab runoff, implying that the dissolved/suspended organic matter in surface waters of the northern Gulf could be quickly injected into the Gulf Deep Water (GDW). [...]"

Source: Marine Pollution Bulletin
Authors: Turki Al-Said et al.
DOI: 10.1016/j.marpolbul.2018.02.013

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Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

Abstract.

"At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific.  [...]"

Source: Biogeosciences
Authors: Birgit Gaye et al.
DOI: 10.5194/bg-15-507-2018

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Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

Abstract.

"The decline in oxygen supply to the ocean associated with global warming is expected to expand 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 indicates strong variations of the Indian monsoon wind intensity over climatic timescales. [...]"

Source: Biogeosciences
Authors: Zouhair Lachkar, Marina Lévy, and Shafer Smith
DOI: 10.5194/bg-15-159-2018

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Bacterial Community Profiling of the Arabian Sea Oxygen Minimum Zone Sediments using Cultivation Independent Approach

Abstract.

"The eastern Arabian Sea has a unique and permanent oxygen minimum zone (OMZ) that extends along the western continental margin of India. In order to understand the bacterial community structure and diversity of OMZ sediment of the Arabian Sea (AS), PCR-DGGE analysis were carried out for samples collected off Ratnagiri, Goa and Karwar at 50m, 200m, 500m and 1000m depths. [...]"

Source: Examines Mar Biol Oceanogr
Authors: Baby Divya, Annie Feby and Shanta Nair

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Oxygen Minimum Zone Contrasts between the Arabian Sea and the Bay of Bengal Implied by Differences in Remineralization Depth

Abstract.

"The combination of high primary productivity and weak ventilation in the Arabian Sea (AS) and Bay of Bengal (BoB) generates vast areas of depleted oxygen, known as Oxygen Minimum Zones (OMZs). The AS OMZ is the world's thickest and hosts up to 40% of global denitrification. In contrast, the OMZ in the BoB is weaker and denitrification free. Using a series of model simulations, we show that the deeper remineralization depth (RD) in the BoB, potentially associated with organic matter aggregation with riverine mineral particles, contributes to weaken its OMZ. [...]"

Source: Geophysical Research Letters
Authors: Muchamad Al Azhar, Zouhair Lachkar, Marina Lévy, Shafer Smith
DOI: 10.1002/2017GL075157

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