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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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Marine N2O emissions from nitrification [...] constrained by modern observations and projected in multi-millennial global warming simula

Abstract.

"Nitrous oxide (N2O) is a potent greenhouse gas (GHG) and ozone destructing agent, yet, global estimates of N2O emissions are uncertain. Marine N2O stems from nitrification and denitrification processes which depend on organic matter cycling and dissolved oxygen (O2). We introduce N2O as an obligate intermediate product of denitrification and as an O2-dependent byproduct from nitrification in the Bern3D ocean model. [...]"

Source: Global Biogeochemical Cycles
Authors: G. Battaglia, F. Joos
DOI: 10.1002/2017GB005671

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Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

Abstract.

"The upwelling system off central Chile (36.5° S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30–50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. [...]"

Source: Biogeosciences
Authors: Alexander Galán et al.
DOI: 10.5194/bg-14-4795-2017

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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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Nitrogen losses in sediments of the East China Sea: Spatiotemporal variations, controlling factors and environmental implications

Abstract.

"Global reactive nitrogen (N) has increased dramatically in coastal marine ecosystems over the past decades and caused numerous eco-environmental problems. Coastal marine sediment plays a critical role in N losses via denitrification and anaerobic ammonium oxidation (anammox) and release of nitrous oxide (N2O). However, both the magnitude and contributions of denitrification, anammox, and N2O production in sediments still remain unclear, causing uncertainty in defining the N budget for coastal marine ecosystems. [...]"

Source: Biogeosciences
Authors: Xianbiao Lin et al.
DOI: 10.1002/2017JG004036

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N2 production by the anammox reaction in the anoxic water column of Golfo Dulce, Costa Rica

Abstract.

"In oxygen-depleted zones of the open ocean, and in anoxic basins and fjords, denitrification (the bacterial reduction of nitrate to give N2) is recognized as the only significant process converting fixed nitrogen to gaseous N2. Primary production in the oceans is often limited by the availability of fixed nitrogen such as ammonium or nitrate, and nitrogen-removal processes consequently affect both ecosystem function and global biogeochemical cycles. [...]"

Source: Nature (2003)
Authors: Tage Dalsgaard et al.
DOI: 10.1038/nature01526


Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

Abstract.

"The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. [...]"

Source: Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Authors: Haojia Ren et al.
DOI: 10.1073/pnas.1701315114

Full article


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 m and 1200 m. Active denitrification in this OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase from early to late Holocene which is contrary to the trend in other regions of water column denitrification. We calculated composite sea surface temperature (SST) and δ15N in time slices of 1000 years of the last 25 ka to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. [...]"

Source: Biogeosciences (under review)
Authors: Birgit Gaye et al.
DOI: 10.5194/bg-2017-256

Full article


Community composition of nitrous oxide consuming bacteria in the oxygen minimum zone of the Eastern Tropical South Pacific

Abstract.

"The ozone-depleting and greenhouse gas, nitrous oxide (N2O), is mainly consumed by the microbially mediated anaerobic process, denitrification. N2O consumption is the last step in canonical denitrification, and is also the least O2 tolerant step. Community composition of total and active N2O consuming bacteria was analyzed based on total (DNA) and transcriptionally active (RNA) nitrous oxide reductase (nosZ) genes using a functional gene microarray. The total and active nosZ communities were dominated by a limited number of nosZ archetypes, affiliated with bacteria from marine, soil and marsh environments. [...]"

Source: Frontiers in Microbiology
Authors: Xin Sun, Amal Jayakumar and Bess B. Ward
DOI: 10.3389/fmicb.2017.01183

Full article


Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Abstract.

"A major percentage of fixed nitrogen (N) loss in the oceans occurs within nitrite-rich oxygen minimum zones (OMZs) via denitrification and anammox. It remains unclear to what extent ammonium and nitrite oxidation co-occur, either supplying or competing for substrates involved in nitrogen loss in the OMZ core. Assessment of the oxygen (O2) sensitivity of these processes down to the O2 concentrations present in the OMZ core (<10 nmol⋅L−1) is therefore essential for understanding and modeling nitrogen loss in OMZs. We determined rates of ammonium and nitrite oxidation in the seasonal OMZ off Concepcion, Chile at manipulated O2 levels between 5 nmol⋅L−1 and 20 μmol⋅L−1. [...]"

Source: Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Authors: Laura A. Bristow et al.
DOI: 10.1073/pnas.1600359113

Full article


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