News

Diversity of culturable Sulphur-oxidising bacteria in the oxygen minimum zones of the northern Indian Ocean

Abstract.

"Oxygen minimum zones (OMZs) are unique, widely spread and well-studied features of the global ocean, varying in seasonality and intensity. The Northern Indian Ocean contains OMZs in the Arabian Sea (AS-OMZ) and the Bay of Bengal (BB-OMZ) having unique biogeochemical features. OMZ water column harbours distinct microbial communities that play vital roles in ocean biogeochemical cycles. Sulphur cycling processes facilitated by OMZ microbial communities are poorly understood with regards to different microbial groups involved, spatially and temporally. [...]"

Source: Journal of Marine Systems (2018)
Authors: Larissa Menezes et al.
DOI: 10.1016/j.jmarsys.2018.05.007

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Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone

Abstract.

"Oxygen minimum zones are expanding globally, and at present account for around 20–40% of oceanic nitrogen loss. Heterotrophic denitrification and anammox—anaerobic ammonium oxidation with nitrite—are responsible for most nitrogen loss in these low-oxygen waters. Anammox is particularly significant in the eastern tropical South Pacific, one of the largest oxygen minimum zones globally. "

Source: Nature Geoscience (2013)
Authors: Tim Kalvelage et al.
DOI: 10.1038/ngeo1739

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Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific

Abstract.

"Over the past decades, observations have confirmed decreasing oxygen levels and shoaling of oxygen minimum zones (OMZs) in the tropical oceans. Such changes impact the biogeochemical cycling of micronutrients such as Cd, but the potential consequences are only poorly constrained. Here, we present seawater Cd concentrations and isotope compositions for 12 depth profiles at coastal, nearshore and offshore stations from 4°S to 14°S in the eastern tropical South Pacific, where one of the world's strongest OMZs prevails. [...]"

Source: Earth and PLanetary Science Letters
Authors: Ruifang C. Xie et al.
DOI: 10.1016/j.epsl.2019.02.001

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Anammox and denitrification in the oxygen minimum zone of the eastern South Pacific

Abstract.

"We quantified the removal of fixed nitrogen as N2 production by anammox and N2 and N2O production by denitrification over a distance of 1900 km along the coasts of Chile and Peru, using short‐term incubations with 15N‐labeled substrates. The eastern South Pacific contains an oxygen minimum zone (OMZ) characterized by an anoxic, nitrate‐ and nitrite‐rich layer of ∼ 200‐m thickness below 30–90 m of oxic water. [...]"

Source: Limnology and Oceanography
Authors: Tage Dalsgaard et al.
DOI: 10.4319/lo.2012.57.5.1331

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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

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Fixed nitrogen loss from the eastern tropical North Pacific and Arabian Sea oxygen deficient zones determined from measurements of N2:Ar

Abstract.

"Previous work estimating the N2excess above background due to denitrification has suggested that nitrate deficit-type methods may be an underestimate of fixed nitrogen (N) loss in the major oxygen deficient zones of the ocean. The N2excess approach has the advantage over nitrate deficit-type methods in that it does not depend on stoichiometric assumptions of fixed N to phosphate or oxygen utilization and avoids any uncertainly regarding the pathway of N loss. [...]"

Source: Global Geochemical Cycles (2012)
Authors: Bonnie X. Chang, Allan H. Devol and Steven R. Emerson
DOI: 10.1029/2011GB004207

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Vertical partitioning of nitrogen-loss processes across the oxic-anoxic interface of an oceanic oxygen minimum zone

Abstract.

"We investigated anammox, denitrification and dissimilatory reduction of nitrite to ammonium (DNRA) activity in the Eastern Tropical South Pacific oxygen minimum zone (OMZ) off northern Chile, at high‐depth resolution through the oxycline into the anoxic OMZ core. This was accompanied by high‐resolution nutrient and oxygen profiles to link changes in nitrogen transformation rates to physicochemical characteristics of the water column. Denitrification was detected at most depths, but anammox was the most active N2‐producing process, while DNRA was not detectable. [...]"

Source: Environmental Microbiology
Authors: Loreto De Brabandere et al.
DOI: 10.1111/1462-2920.12255

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The impact of primary and export production on the formation of the secondary nitrite maximum: A model study

Abstract.

"The so-called secondary nitrite maximum (SNM) is a pronounced subsurface feature in many oxygen deficient zones of the ocean. A nitrite layer of up to several hundred meters thickness indicates high microbial activity and nitrogen loss from the system. To study the effects of primary and export production on the SNM, we have developed a one-dimensional ecosystem model for oxygen deficient zones. Our model couples the marine nitrogen and oxygen cycles with physical water column processes, includes euphotic, aphotic, aerobic and anaerobic processes and thereby dynamically describes source and sink processes for nitrite. [...]"

Source: Ecological Modelling
Authors: Aike Beckmann and Inga Hense
DOI: 10.1016/j.ecolmodel.2017.05.014

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Metabolic preference of nitrate over oxygen as an electron acceptor in foraminifera from the Peruvian oxygen minimum zone

Abstract.

"Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO3−) or oxygen (O2)—makes them important mediators of benthic nitrogen cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O2 respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). [...]"

Source: PNAS
Authors: Nicolaas Glock et al.
DOI: 10.1073/pnas.1813887116

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Job Offer: Postdoctoral Researcher

Postdoctoral Researcher in the area of ocean physical and biogeochemical coupling to work with Professor Resplandy in the Princeton University Geosciences department. The postdoc will investigate the physical and biological processes at both global and local scale that control the evolution of the tropical Oxygen Minimum Zone in the Indian Ocean. Details of the project can be found at https://environment.princeton.edu/grandchallenges/research/energy/dead_zones. Ideally, candidates will have a strong background in numerical modeling, but candidates with the necessary background in geophysical fluid dynamics and/or ocean biogeochemistry will be given full consideration.

Applicants should include a cover letter, a curriculum vitae including a publication list, and contact information for three references by applying at https://www.princeton.edu/acad-positions/position/9941. Applications should be received by April 15, 2019.


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