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Latitudinal variations in δ30Si and δ15N signatures along the Peruvian shelf: quantifying the effects of nutrient utilization versus denitrification..

..over the past 600 years

Abstract.

"The stable sedimentary nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and the 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 (δ15NO−3) upwelled to the surface. [...]"

Source: Biogeosciences
Authors: Kristin Doering et al.
DOI: 10.5194/bg-16-2163-2019

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Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria

Abstract.

"Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (15ε and 18ε) associated with the respective nitrogen transformation processes must be known. [...]"

Source: The ISME Journal
Authors: Kanae Kobayashi et al.
DOI: 10.1038/s41396-019-0440-x

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Isotopic fingerprints of benthic nitrogen cycling in the Peruvian oxygen minimum zone

Abstract.

"Stable isotopes (15,14N, 18,16O) of dissolved inorganic nitrogen (N) were measured in sediment porewaters and benthic flux chambers across the Peruvian oxygen minimum zone (OMZ) from 74 to 1000 m water depth. Sediments at all locations were net consumers of bottom water NO3−. In waters shallower than 400 m, this sink was largely attributed to dissimilatory nitrate reduction to ammonium (DNRA) by filamentous nitrate-storing bacteria (Marithioploca and Beggiatoa) and to denitrification by foraminifera. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: A.W.Dale et al.
DOI: 10.1016/j.gca.2018.10.025

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Marine ammonification and carbonic anhydrase activity induce rapid calcium carbonate precipitation

Abstract.

"During Earth’s history, precipitation of calcium carbonate by heterotrophic microbes has substantially contributed to the genesis of copious amounts of carbonate sediment and its subsequent lithification. Previous work identified the microbial sulfur and nitrogen cycle as principal pathways involved in the formation of marine calcium carbonate deposits. While substantial knowledge exists for the importance of the sulfur cycle, specifically sulfate reduction, with regard to carbonate formation, information about carbonate genesis connected to the microbial nitrogen cycle is dissatisfactory. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: S. Krause et al
DOI: 10.1016/j.gca.2018.09.018

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Redox condition and nitrogen cycle in the Permian deep mid-ocean: A possible contrast between Panthalassa and Tethys

Abstract.

"To constrain the redox conditions and related nitrogen cycles during the Middle Permian (Guadalupian) to latest Late Permian (Lopingian) deep mid-Panthalassa, we determined the abundances of major, trace, and rare earth elements along with the carbon and nitrogen isotope ratios in shales interbedded with deep-sea cherts that are well-exposed at the Gujo-Hachiman section in the Mino-Tanba belt, SW Japan. [...]"

Source: Global and Planetary Change
Authors: Wataru Fujisaki et al.
DOI: 10.1016/j.gloplacha.2018.09.015

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Lipids as indicators of nitrogen cycling in present and past anoxic oceans

Summary.

"Nitrogen (N) cycling influences primary production in the ocean and, hence, the global climate. It is performed by a variety of microorganisms, including eukaryotes, bacteria and archaea in oxic, suboxic, and anoxic waters. Our knowledge of the reactions involved in marine N cycling and its associated microorganisms has greatly increased in the last decade due to the development of multiple culture-independent methods. Among them are gene and lipid biomarkers, which hold taxonomic potential and can be successfully applied in modern day and paleoenvironmental studies. However, many aspects of N cycling and their long-term implications for the marine environment and the global climate still require more study, especially in suboxic and anoxic waters, including the oxygen-deficient zones (ODZs), which are expanding in the modern oceans.

Author: Martina Sollai

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Back to the future of climate change

Summary:

Researchers are looking to the geologic past to make future projections about climate change. Their research focuses on the ancient Tethys Ocean (site of the present-day Mediterranean Sea) and provides a benchmark for present and future climate and ocean models.

Source: Science Daily

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Perturbation to the nitrogen cycle during rapid Early Eocene global warming

Abstract.

"The degree to which ocean deoxygenation will alter the function of marine communities remains unclear but may be best constrained by detailed study of intervals of rapid warming in the geologic past. The Paleocene–Eocene Thermal Maximum (PETM) was an interval of rapid warming that was the result of increasing contents of greenhouse gases in the atmosphere that had wide ranging effects on ecosystems globally. Here, we present stable nitrogen isotope data from the Eastern Peri-Tethys Ocean that record a significant transition in the nitrogen cycle.  [...]"

Source: Nature Communications
Authors: Christopher K. Junium, Alexander J. Dickson & Benjamin T. Uveges 
DOI: 10.1038/s41467-018-05486-w

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Single cell genomic and transcriptomic evidence for the use of alternative nitrogen substrates by anammox bacteria

Abstract.

"Anaerobic ammonium oxidation (anammox) contributes substantially to ocean nitrogen loss, particularly in anoxic marine zones (AMZs). Ammonium is scarce in AMZs, raising the hypothesis that organic nitrogen compounds may be ammonium sources for anammox. Biochemical measurements suggest that the organic compounds urea and cyanate can support anammox in AMZs. [...]"

Source: The ISME Journal
Authors: Sangita Ganesh et al.
DOI: 10.1038/s41396-018-0223-9

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Coupling of ocean redox and animal evolution during the Ediacaran-Cambrian transition

Abstract.

"The late Ediacaran to early Cambrian interval witnessed extraordinary radiations of metazoan life. The role of the physical environment in this biological revolution, such as changes to oxygen levels and nutrient availability, has been the focus of longstanding debate. Seemingly contradictory data from geochemical redox proxies help to fuel this controversy. As an essential nutrient, nitrogen can help to resolve this impasse by establishing linkages between nutrient supply, ocean redox, and biological changes. [...]"

Source: Nature Communications
Authors: Dan Wang et al.
DOI: 10.1038/s41467-018-04980-5

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