Autonomous profiling float observations reveal the dynamics of deep biomass distributions in the denitrifying oxygen minimum zone of the Arabian Sea
"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.
Oxygen variability controls denitrification in the Bay of Bengal oxygen minimum zone
"Nitrate limits productivity in much of the ocean. Nitrate residence time is a few thousand years and changes in nitrate loss could influence ocean productivity. A major sinks for nitrate is denitrification and anaerobic ammonia oxidation in the oxygen minimum zones (OMZs). The Bay of Bengal OMZ is anomalous because large amounts of nitrate loss do not occur there, while nitrate is removed in the nearby OMZ of the Arabian Sea. Observations of nitrate and oxygen made over 5 years by 20 profiling floats equipped with chemical sensors in the Bay of Bengal and the Arabian Sea are used to understand why nitrate is removed rapidly in the Arabian Sea, but not in the Bay of Bengal. [...]"
Source: Geophysical Research Letters
Authors: Kenneth S. Johnson, Stephen C. Riser and M. Ravichandran
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.
Ventilation of oxygen to oxygen minimum zone due to anticyclonic eddies in the Bay of Bengal
"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. [...]"
Authors: V. V. S. S. Sarma, T. V. S. Udaya Bhaskar
Enhanced carbon-sulfur cycling in the sediments of Arabian Sea oxygen minimum zone center
"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.
Physical controls on oxygen distribution and denitrification potential in the north west Arabian Sea
"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.
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
High total organic carbon in surface waters of the northern Arabian Gulf: Implications for the oxygen minimum zone of the Arabian Sea
"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.
Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification
"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. [...]"
Authors: Birgit Gaye et al.
Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity
"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. [...]"
Authors: Zouhair Lachkar, Marina Lévy, and Shafer Smith