Temperature Decouples Ammonium and Nitrite Oxidation in Coastal Waters
"Nitrification is a two-step process linking the reduced and oxidized sides of the nitrogen cycle. These steps are typically tightly coupled with the primary intermediate, nitrite, rarely accumulating in coastal environments. Nitrite concentrations can exceed 10 μM during summer in estuarine waters adjacent to Sapelo Island, Georgia, U.S.A. Similar peaks at other locations have been attributed to decoupling of the two steps of nitrification by hypoxia; however, the waters around Sapelo Island are aerobic and well-mixed. Experiments examining the response to temperature shifts of a nitrifying assemblage composed of the same organisms found in the field indicate that ammonia- and nitrite-oxidation become uncoupled between 20 and 30 °C, leading to nitrite accumulation. [...]"
Source: Environmental Science & Technology
Authors: Sylvia C. Schaefer, James T. Hollibaugh
New Species of Ciliates (Genus: Strombidium sp.) from hypoxic waters of the Bay of Bengal, Northern Indian Ocean
"Present study describes a new species of Strombidium (oligotrich ciliates) found in the cold sub-surface (125m below surface) oxic-hypoxic boundary of the Bay of Bengal. We name it as Strombidium mansai and describe its morphology."
[...] "The biological productivity of Bay of Bengal is governed by mesoscale eddies and tropical cyclones that trigger occasional higher productivity that could also add to the consumption of dissolved nutrients at sub-surface depth. These zones of hypoxic waters are found to be dominated by large number of bacterial community probavly driving unique microbial community in the Idian Ocean."
Source: Indian Journal of Geo Marine Science
Authors: Sai Elangovan, Mangesh Gauns
Deoxygenation of the Baltic Sea during the last century
"Deoxygenation is a global problem in coastal and open regions of the ocean, and has led to expanding areas of oxygen minimum zones and coastal hypoxia. The recent expansion of hypoxia in coastal ecosystems has been primarily attributed to global warming and enhanced nutrient input from land and atmosphere. The largest anthropogenically induced hypoxic area in the world is the Baltic Sea, where the relative importance of physical forcing versus eutrophication is still debated. We have analyzed water column oxygen and salinity profiles to reconstruct oxygen and stratification conditions over the last 115 y and compare the influence of both climate and anthropogenic forcing on hypoxia. [...]"
Source: Procedings of the National Academy of Sciences of the United States of America (PNAS)
Authors: Jacob Carstensen et al.
Decadal dynamics and predictability of oxygen and subsurface tracers in the California Current System
"The oxygen of the source waters that feed the upwelling in the California Current System show prominent multi-decadal fluctuations that are not significantly correlated with the dominant modes of Pacific climate variability. By combining observations and ocean reanalysis products between 1950-2010, we show that decadal changes in oxygen are linked to subsurface salinity variability and primarily controlled by ocean circulation dynamics. We find that subsurface anomalies in the core of the North Pacific Current propagate the oxygen signal downstream into the coastal upwelling system following the path of the mean gyre circulation with a timescale of 10-years. [...]"
Source: Geophysical Reasearch Letters
Authors: Mercedes Pozo Buil, Emanuele Di Lorenzo
Aerobic and anaerobic ammonium oxidizers in the Cariaco Basin: distributions of major taxa and nitrogen species across the redoxcline
"Depth distributions of cells and functional gene copies from anaerobic ammonium-oxidizing (anammox) bacteria, aerobic ammonium-oxidizing bacteria (AOB) and archaea (AOA) in the Cariaco Basin, Venezuela were obtained using FISH and q-PCR assays. These distributions were compared to concentrations of dissolved ammonium (NH4+), nitrite (NO2-), nitrate (NO3-), hydrogen sulfide (H2S) and oxygen (O2) along the redoxcline during 3 cruises. Cell counts of anammox bacteria and copies of their nitrite reductase gene (Scalindua-nirS) were consistently observed in 2 distinct layers: the suboxic zone (≤1.1 × 106 cells l-1) and the upper euxinic zone (≤4.7 × 106 cells l-1). [...]"
Source: Aquatic Microbial Ecology 79
Authors: Sara Cernadas-Martín et al.
Big Storms Pump Mediterranean Water Far into the Black Sea
"For the first time, scientists provide a sea-wide view of what happens to Mediterranean waters that flow into the Black Sea through the Bosporus Strait.
Below a depth of about 150 meters, the Black Sea is devoid of oxygen. Only certain microbes can survive in this “dead zone,” which reaches depths of over 2000 meters. Warm, salty water flowing from the Mediterranean Sea into the Black Sea ventilates the middepth water column of the sea, trapping anoxic water below and maintaining the sea’s distinctive structure. However, the precise fate of inflowing Mediterranean waters has remained something of a mystery to scientists. [...]"
Author: Sarah Stanley
A three-dimensional model of the marine nitrogen cycle during the Last Glacial Maximum constrained by sedimentary isotopes
"Nitrogen is a key limiting nutrient that influences marine productivity and carbon sequestration in the ocean via the biological pump. In this study, we present the first estimates of nitrogen cycling in a coupled 3D ocean-biogeochemistry-isotope model forced with realistic boundary conditions from the Last Glacial Maximum (LGM) ~21,000 years before present constrained by nitrogen isotopes. The model predicts a large decrease in nitrogen loss rates due to higher oxygen concentrations in the thermocline and sea level drop, and, as a response, reduced nitrogen fixation. Model experiments are performed to evaluate effects of hypothesized increases of atmospheric iron fluxes and oceanic phosphorus inventory relative to present-day conditions. [...]"
Source: Frontiers in Marine Science
Authors: Christopher J. Somes et al.
Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic
"In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg−1), supposedly due to reduced heterotrophic activity. [...]"
Source: Biogeosciences 14
Authors: Anja Engel et al.
Response of western South American epeiric-neritic ecosystem to middle Cretaceous Oceanic Anoxic Events
"Little is known about the impact of the mid-Cretaceous Oceanic Anoxic Events (OAEs) on the neritic carbonate systems in South America. In order to fill this knowledge gap, the present paper reports on the record of environmental changes in the Albian–Turonian neritic carbonates from the western South American domain in Peru. Owing to the very expanded and well-exposed sections in the Oyon region of central Peru, the OAE 1d and 2 intervals were sampled at high temporal resolution for both bulk micrite and bulk organic matter carbon isotopes, allowing us to compare the fingerprint of these two events between the northern and central Peruvian regions. [...]"
Source: Cretaceous Research Vol.75
Authors: J.P. Navarro-Ramirez et al.
Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters
"Coastal seas may account for more than 75 % of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from which it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter, reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. [...]"
Source: Biogeosciences 14
Authors: Lea Steinle et al.