Short exposure to oxygen and sulfide alter nitrification, denitrification, and DNRA activity in seasonally hypoxic estuarine sediments
"Increased organic loading to sediments from eutrophication often results in hypoxia, reduced nitrification and increased production of hydrogen sulfide, altering the balance between nitrogen removal and retention. We examined the effect of short-term exposure to various oxygen and sulfide concentrations on sediment nitrification, denitrification and DNRA from a chronically hypoxic basin in Roskilde Fjord, Denmark. Surprisingly, nitrification rates were highest in the hypoxic and anoxic treatments (about 5 μmol cm−3 d−1) and the high sulfide treatment was not significantly different than the oxic treatment. [...]"
Source: FEMS Microbiology Letters
Authors: Jane M. Caffrey, Stefano Bonaglia, Daniel J. Conley
Study of dissolved oxygen responses to tropical cyclones in the Bay of Bengal based on Argo and satellite observations
"Effects of tropical cyclones (TCs) on dissolved oxygen (DO) in subsurface waters (20–200 m) over the Oxygen Minimum Zones (OMZs) in the Bay of Bengal (BoB) are examined based on Argo and satellite data. Five TCs (Hudhud, Five, Vardah, Maarutha and Mora) during 2013–2018 are considered. Analyses reveal three types of DO temporal variability caused by the storm-induced mixing and upwelling. The first type features temporal DO increases in subsurface waters (37–70 m) caused mainly by intense vertical mixing and downwelling. [...]"
Source: Science of the Total Environment
Authors: Huabing Xu et al.
Ocean deoxygenation and zooplankton: Very small oxygen differences matter
"Oxygen minimum zones (OMZs), large midwater regions of very low oxygen, are expected to expand as a result of climate change. While oxygen is known to be important in structuring midwater ecosystems, a precise and mechanistic understanding of the effects of oxygen on zooplankton is lacking. Zooplankton are important components of midwater food webs and biogeochemical cycles. Here, we show that, in the eastern tropical North Pacific OMZ, previously undescribed submesoscale oxygen variability has a direct effect on the distribution of many major zooplankton groups. Despite extraordinary hypoxia tolerance, many zooplankton live near their physiological limits and respond to slight (≤1%) changes in oxygen. [...]"
Source: Science Advances
Authors: K. F. Wishner et al.
URI researchers: Small changes in oxygen levels have big implications for ocean life
Oceanographers at the University of Rhode Island have found that even slight levels of ocean oxygen loss, or deoxygenation, have big consequences for tiny marine organisms called zooplankton.
Zooplankton are important components of the food web in the expanse of deep, open ocean called the midwater. Within this slice of ocean below the surface and above the seafloor are oxygen minimum zones (OMZs), large regions of very low oxygen. Unlike coastal “dead zones” where oxygen levels can suddenly plummet and kill marine life not acclimated to the conditions, zooplankton in OMZs are specially adapted to live where other organisms – especially predators – cannot.
Source: Whats up newp
Home sweet suboxic home: remarkable hypoxia tolerance in two demersal fish species in the Gulf of California
"Extremophiles – organisms that live in extreme environments – invite us to question our assumptions about the requirements for life. Fish, as a group, are thought to be relatively hypoxia intolerant due to their high metabolic requirements (Vaquer‐Sunyer and Duarte 2008); however, the cusk‐eel, Cherublemma emmelas, and the catshark, Cephalurus cephalus, appear to thrive in one of the most extreme low oxygen marine habitats in the world – the Gulf of California. Here, we describe the behavior and habitat of these extraordinary species that live under conditions commonly thought to be uninhabitable by fish. [...]"
Authors: Natalya D. Gallo et al.
Interpreting Mosaics of Ocean Biogeochemistry
"Sea level rise, heat transport, ocean acidification, these ocean processes, well known in the public sphere, play out on a regional to global scale. But less well known are more localized processes that bring some ecological niches together, keep others separated, and help sustain ocean life by circulating nutrients.
Physical processes in the ocean that take place over intermediate and small scales of space and time play a key role in vertical seawater exchange. They also have significant effects on chemical, biological, and ecological processes in the upper ocean. [...]"
High denitrification and anaerobic ammonium oxidation contributes to net nitrogen loss in a seagrass ecosystem in the central Red Sea
"Nitrogen loads in coastal areas have increased dramatically, with detrimental consequences for coastal ecosystems. Shallow sediments and seagrass meadows are hotspots for denitrification, favoring N loss. However, atmospheric dinitrogen (N2) fixation has been reported to support seagrass growth. Therefore, the role of coastal marine systems dominated by seagrasses in the net N2 flux remains unclear. Here, we measured denitrification, anaerobic ammonium oxidation (anammox), and N2 fixation in a tropical seagrass (Enhalus acoroides) meadow and the adjacent bare sediment in a coastal lagoon in the central Red Sea. [...]"
Authors: Neus Garcias-Bonet et al.
Global warming today mirrors conditions leading to Earth's largest extinction event, study says
"More than two-thirds of life on Earth died off some 252 million years ago, in the largest mass extinction event in Earth's history.
Researchers have long suspected that volcanic eruptions triggered "the Great Dying," as the end of the Permian geologic period is sometimes called, but exactly how so many creatures died has been something of a mystery.
Now scientists at the University of Washington and Stanford believe their models reveal how so many animals were killed, and they see frightening parallels in the path our planet is on today.
Models of the effects of volcanic greenhouse gas releases showed the Earth warming dramatically and oxygen disappearing from its oceans, leaving many marine animals unable to breathe, according to a study published Thursday in the peer-reviewed journal Science. By the time temperatures peaked, about 80 percent of the oceans' oxygen, on average, had been depleted. Most marine animals went extinct. [...]"
Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction
"Climate change triggered by volcanic greenhouse gases is hypothesized to have caused the largest mass extinction in Earth’s history at the end of the Permian Period (~252 million years ago). Geochemical evidence provides strong support for rapid global warming and accompanying ocean oxygen (O2) loss, but a quantitative link among climate, species’ traits, and extinction is lacking. To test whether warming and O2 loss can mechanistically account for the marine mass extinction, we combined climate model simulations with an established ecophysiological framework to predict the biogeographic patterns and severity of extinction. Those predictions were confirmed by a spatially explicit analysis of the marine fossil record. [...]"
Authors: Justin L. Penn et al.
A Novel Approach for Measuring the Gulf of Mexico Dead Zone: Toward Better Temporal and Spatial Estimates for Management Applications
"Nearly every summer, a large hypoxic zone forms in the northern Gulf of Mexico. Research on the causes and consequences of hypoxia requires reliable estimates of hypoxic extent, which can vary at submonthly time scales due to hydro-meteorological variability. Here, we use an innovative space-time geostatistical model and data collected by multiple research organizations to estimate bottom-water dissolved oxygen (BWDO) concentrations and hypoxic area across summers from 1985 to 2016. [...]"
Source: Environmental Science and Technology
Authors: V. Rohith Reddy Matli et al.
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