Shedding New Light on the Nitrogen Cycle in the Dark Ocean
"Every year, the Mississippi River dumps around 1.4 million metric tons of nitrogen into the Gulf of Mexico, much of it runoff from agricultural fertilizer. This nitrogen can lead to algal blooms, which in turn deplete oxygen concentrations in the water, creating hypoxic dead zones. The nitrogen cycle is a phenomenon environmental scientists would really like to understand better. “As humans, we do put a lot of reactive nitrogen compounds into the ocean, especially in coastal regions, by…river runoff,” said Katharina Kitzinger of the Max Planck Institute for Marine Microbiology in Bremen, Germany. “It’s really crucial to understand how microbes turn over this excess nitrogen that we put into the environment. [...]”"
Warming stimulates sediment denitrification at the expense of anaerobic ammonium oxidation
"Temperature is one of the fundamental environmental variables governing microbially mediated denitrification and anaerobic ammonium oxidation (anammox) in sediments. The GHG nitrous oxide (N2O) is produced during denitrification, but not by anammox, and knowledge of how these pathways respond to global warming remains limited. [...]"
Source: Nature Climate Change
Authors: Ehui Tan et al.
Understanding Long Island Sound's 'dead zones'
"For the past 25 years, the Environmental Protection Agency and the Connecticut Department of Energy and Environmental Protection have been diligently collecting water samples each month in Long Island Sound (LIS). Recently, the data have been compiled and analyzed, by UConn associate professors of Marine Science Penny Vlahos and Michael Whitney, and other team members, who have begun the task of digging into the data to better understand the biogeochemistry of the Sound. Part of the analysis, called "Nitrogen Budgets for LIS," has been published in the journal Estuarine, Coastal and Shelf Science. [...]"
Implications of different nitrogen input sources for potential production and carbon flux estimates in the coastal Gulf of Mexico (GOM)
and Korean Peninsula coastal waters
"The coastal Gulf of Mexico (GOM) and coastal sea off the Korean Peninsula (CSK) both suffer from human-induced eutrophication. We used a nitrogen (N) mass balance model in two different regions with different nitrogen input sources to estimate organic carbon fluxes and predict future carbon fluxes under different model scenarios. The coastal GOM receives nitrogen predominantly from the Mississippi and Atchafalaya rivers and atmospheric nitrogen deposition is only a minor component in this region. [...]"
Source: Ocean Science
Authors: Jongsun Kim et al.
Quantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China Sea
"In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m−3) is frequently observed off the Changjiang (or Yangtze) River estuary covering up to about 15,000 km2. The Changjiang River is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modelling and observational studies have suggested that intrusions of nutrient-rich oceanic water from the Kuroshio also contribute to hypoxia formation. [...]"
Source: Biogeosciences (preprint)
Authors: Fabian Große et al.
Latitudinal variations in δ30Si and δ15N signatures along the Peruvian shelf: quantifying the effects of nutrient utilization versus denitrification..
..over the past 600 years
"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. [...]"
Authors: Kristin Doering et al.
Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria
"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.
Isotopic fingerprints of benthic nitrogen cycling in the Peruvian oxygen minimum zone
"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.
Marine ammonification and carbonic anhydrase activity induce rapid calcium carbonate precipitation
"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
Redox condition and nitrogen cycle in the Permian deep mid-ocean: A possible contrast between Panthalassa and Tethys
"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.