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Latitudinal variations of δ30Si and δ15N signatures along the Peruvian shelf:

quantifying the effects of nutrient utilization versus denitrification over the past 600 years

Abstract. 

"The sedimentary stable nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO3) upwelled to the surface. [...]"

Source: Biogeosciences
Authors: Kristin Doering et al.
DOI: 10.5194/bg-2018-118

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Global niche of marine anaerobic metabolisms expanded by particle microenvironments

Abstract.

"In ocean waters, anaerobic microbial respiration should be confined to the anoxic waters found in coastal regions and tropical oxygen minimum zones, where it is energetically favourable. However, recent molecular and geochemical evidence has pointed to a much broader distribution of denitrifying and sulfate-reducing microbes. [...]"

Source: Nature Geoscience
Authors: Daniele Bianchi et al.
DOI: 10.1038/s41561-018-0081-0

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Influence of an oxygen minimum zone and macroalgal enrichment on benthic megafaunal community composition in a NE Pacific submarine canyon

Abstract.

"Megafaunal diversity in the deep sea shows a parabolic pattern with depth. It can be affected by factors such as low oxygen concentration, which suppresses diversity, or the presence of submarine canyons, which enhances it. Barkley Canyon, located off the west coast of British Columbia, Canada, is a submarine canyon that extends from the continental margin (200 m) into the deep ocean (2,000 m).  [...]"

Source: marine ecology
Authors: Lia Domke et al.
DOI: 10.1111/maec.12481

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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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New measurement technology helps to determine NO concentrations in the ocean

"Nitrogen monoxide (NO) belongs to the group of nitrogen oxides which are infamous as toxic emissions in urban agglomerations. But NO is also produced in nature and plays a role in the nitrogen cycle. However, from earth's largest ecosystem, the ocean, we have hardly any NO measurements."

Source: Science Daily

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Nitric oxide (NO) in the oxygen minimum zone off Peru

Abstract.

"Nitric oxide (NO) is a short-lived compound of the marine nitrogen cycle. However, measurements of NO in seawater are analytically challenging and our knowledge about its oceanic distribution is, therefore, rudimentary. NO was measured in the oxygen minimum zone (OMZ) of the eastern tropical South Pacific Ocean (ETSP) off Peru during R/V Meteor cruise M93 in February/March 2013. [...]"

Source: Deep Sea Research Part II: Topical Studies in Oceanography
Authors: Hannah E. Lutterbeck et al.
DOI: 10.1016/j.dsr2.2017.12.023

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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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Metabolic versatility of a novel N2-fixing Alphaproteobacterium isolated from a marine oxygen minimum zone

Abstract.

"The N2-fixing (diazotrophic) community in marine ecosystems is dominated by non-cyanobacterial microorganisms. Yet, very little is known about their identity, function and ecological relevance due to a lack of cultured representatives. Here we report a novel heterotrophic diazotroph isolated from the oxygen minimum zone (OMZ) off Peru. [...]"

Source: environmental microbiology
Authors: Clara Martínez-Pérez et al.
DOI: 10.1111/1462-2920.14008

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Patterns of deoxygenation: sensitivity to natural and anthropogenic drivers

Abstract.

"Observational estimates and numerical models both indicate a significant overall decline in marine oxygen levels over the past few decades. Spatial patterns of oxygen change, however, differ considerably between observed and modelled estimates. Particularly in the tropical thermocline that hosts open-ocean oxygen minimum zones, observations indicate a general oxygen decline, whereas most of the state-of-the-art models simulate increasing oxygen levels. Possible reasons for the apparent model-data discrepancies are examined. [...]"

Source: Philosophical Transactions of the Royal Socie
Authors: Andreas Oschlies et al.
DOI: 10.1098/rsta.2016.0325

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