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Variability of the oxygen minimum zone associated with primary productivity and hydrographic conditions in the Eastern North Pacific

Abstract. 

"The expansion of the oxygen minimum zone (OMZ) associated with global warming has generated interest in its variability during the last two millennia. Several oceanographic mechanisms, as advection of dissolved oxygen and depletion of dissolved oxygen by oxidation of exported marine productivity, could explain the variability of δ15N in organic matter as a denitrification indicator of the water column in the Pacific Ocean. Our objective was to infer local or remote forcing mechanisms that lead to the strengthening or weakening of the OMZ in the Eastern Tropical North Pacific. [...]". 

 

Source: Science Direct 
Authors: Alberto Sánchez et al.
DOI: https://doi.org/10.1016/j.dsr.2022.103810

Read the full article here.


Mercury stable isotopes suggest reduced foraging depth in oxygen minimum zones for blue sharks

Abstract. 

"Oxygen minimum zones (OMZs) are currently expanding across the global ocean due to climate change, leading to a compression of usable habitat for several marine species. Mercury stable isotope compositions provide a spatially and temporally integrated view of marine predator foraging habitat and its variability with environmental conditions. Here, we analyzed mercury isotopes in blue sharks Prionace glauca from normoxic waters in the northeastern Atlantic and from the world's largest and shallowest OMZ, located in the northeastern Pacific (NEP). [...]".

 

Source: Science Direct 
Authors: Gaël Le Croizier et al.
DOI: https://doi.org/10.1016/j.marpolbul.2022.113892

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Oxygen minimum zone copepods in the Arabian Sea and the Bay of Bengal: Their adaptations and status

Abstract.

"The Arabian Sea and the Bay of Bengal are cul-de-sacs of the northern Indian Ocean, and they contain more than half of the world's Oxygen Minimum Zones (OMZs). The current study reviews the vast and advancing literature on the oceanographic settings that lead to distinct OMZs in the Arabian Sea and the Bay of Bengal and links them with the copepods thriving there, their status, and likely adaptations. The Arabian Sea has a thicker perennial subsurface OMZ (∼1000 m) than the Bay of Bengal (∼500 m), which is linked to high plankton production via upwelling and winter convection in the former and river influx and mesoscale eddies in the latter. [...]."

 

Source: Science Direct 
Authors: Vidhya Vijayasenan et al.
DOI: https://doi.org/10.1016/j.pocean.2022.102839

Read the full article here.


Spatio-temporal variations in culturable bacterial community associated with denitrification in the Arabian Sea oxygen minimum zone

Abstract. 

"The Arabian Sea (AS) oxygen minimum zone (OMZ) is a site of intense denitrification, contributing to 20% of the global oceanic denitrification, playing a significant role in the nitrogen cycle. In this study, the structure and diversity of culturable bacterial communities inhabiting the water column of the AS OMZ were investigated through phylogenetic analysis and nitrate-utilizing ability was studied through culture-based studies. A total of 248 isolates collected during pre-monsoon and post-monsoon season were analysed for 16S rRNA gene sequences. [...]".

 

Source: Marine Biology Research
Authors: Ujwala Amberkar et al. 
DOI: 10.1080/17451000.2022.2086700

Read the full article here.


Deglacial restructuring of the Eastern equatorial Pacific oxygen minimum zone

Abstract. 

"Oxygenation in the Eastern Equatorial Pacific is responsive to ongoing climate change in the modern ocean, although whether the region saw a deglacial change in extent or position of the Oxygen Minimum Zone remains poorly constrained. Here, stable isotopes from the shells of an Oxygen Minimum Zone-dwelling planktic foraminifer are used to reassess the position of the mid-water Oxygen Minimum Zone relative to both the thermocline and benthos. Oxygen isotopes record a rapid shoaling of the Oxygen Minimum Zone towards the thermocline associated with Heinrich Stadial 1 and persisting through the deglaciation. [...]". 

 

Source: Communications Earth & Environment
Authors: Catherine V. Davis
DOI: https://doi.org/10.1038/s43247-022-00477-8

Read the full article here.


Insights into prokaryotic community and its potential functions in nitrogen metabolism in the Bay of Bengal, a pronounced Oxygen Minimum Zone

Abstract. 

"Ocean oxygen minimum zones (OMZs) around the global ocean are expanding both horizontally and vertically. Multiple studies have identified the significant influence of anoxic conditions (≤1 μM O2) on marine prokaryotic communities and biogeochemical cycling of elements. However, little attention has been paid to the expanding low-oxygen zones where the oxygen level is still above the anoxic level. Here, we studied the abundance and taxonomic and functional profiles of prokaryotic communities in the Bay of Bengal (BoB), where the oxygen concentration is barely above suboxic level (5 μM O2). [...]". 

 

Source: Microbiology Spectrum
Authors: Bowei Gu et al. 
DOI: https://doi.org/10.1128/spectrum.00892-21

Read the full article here.


Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

Abstract. 

"We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). [...]". 

 

Source: Science Direct 
Authors: Carlos A. Alvarez Zarikian et al.
DOI: https://doi.org/10.1016/j.marmicro.2022.102105

Read the full article here.


Trace elements V, Ni, Mo and U: A geochemical tool to quantify dissolved oxygen concentration in the oxygen minimum zone of the north-eastern Pacific

Abstract.

"Deoxygenation of the water column in the oceans and in the oxygen minimum zone (OMZ) has become relevant due to its connection with global climate change. The variability of the OMZ has been inferred by in situ measurements for the last 70 years and qualitatively assessed through the monitoring of trace elements and the nitrogen stable isotope ratio (δ15N) of organic matter on several time scales. The V, Ni, Mo and U concentrations in surface sediments and the dissolved oxygen concentration in the water column of La Paz Bay and the Mazatlán margin were used to propose an exponential regression model. This model will allow the inference of the dissolved oxygen concentration in the sedimentary records from the Alfonso Basin in La Paz Bay and in the Mazatlán margin over the last 250 years. [...]".

 

Source: Science Direct
Authors: Alberto Sánchez et al. 
DOI: https://doi.org/10.1016/j.jmarsys.2022.103732

Read the full article here.


Geochemistry of sediments in contact with oxygen minimum zone of the eastern Arabian Sea: Proxy for palaeo-studies

Abstract. 

"The Arabian Sea encompasses oxygen minimum zone with denitrifying conditions. For the present study, sediments were collected across three transects off Goa transect (GT), Mangalore transect (MT) and Kochi transect (KT) in contact with water column dissolved oxygen (DO) range of 1.4–118.0 µM. Sediments were investigated for texture, clay mineralogy, total organic carbon (Corg), total nitrogen, CaCO3, δ15N, δ13C, metal content to infer their distribution with changing DO and their use as possible palaeo-proxies. The Corg (0.9–8.6%) is largely marine and δ15N from GT and MT preserves signatures of higher water column denitrification. [...]". 

 

Source: Journal of Earth System Science 

Authors: Pratima M. Kessarkar et al. 

DOI: https://doi.org/10.1007/s12040-022-01823-2 

Read the full article here.


Anaerobic methane oxidation in a coastal oxygen minimum zone: spatial and temporal dynamics

Abstract. 

"Coastal waters are a major source of marine methane to the atmosphere. Particularly high concentrations of this potent greenhouse gas are found in anoxic waters, but it remains unclear if and to what extent anaerobic methanotrophs mitigate the methane flux. Here we investigate the long-term dynamics in methanotrophic activity and the methanotroph community in the coastal oxygen minimum zone (OMZ) of Golfo Dulce, Costa Rica, combining biogeochemical analyses, experimental incubations and 16S rRNA gene sequencing over 3 consecutive years. [...]".

 

Source: Environmental Microbiology

Authors: Herdís G. R. Steinsdóttir et al. 

DOI: https://doi.org/10.1111/1462-2920.16003

Read the full article here.


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