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Effects of Coastal Upwelling and Downwelling on Hydrographic Variability and Dissolved Oxygen in Mobile Bay

Abstract.

"Upwellling and downwelling events are important coastal processes that strongly influence shelf ecosystem dynamics. Though changes on the shelf have been well studied, the impact of these events on estuarine systems has received less focus. In summer 2016 a downwelling and upwelling event were observed near the mouth of Mobile Bay. The impact of these events were examined throughout the bay with high spatial resolution observations. Five boat surveys were conducted to capture the spatial response of offshore forcing and its changes in the estuary. In addition to the surveys, 16 CTDs were deployed and measured temporal changes. [...]"

Source: JGR Oceans
Authors: Jeffrey Coogan, Brian Dzwonkowski and John Lehrter
DOI: 10.1029/2018JC014592

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Southern Hemisphere sea-surface temperatures during the Cenomanian–Turonian: Implications for the termination of Oceanic Anoxic Event 2

Abstract.

"Mesozoic oceanic anoxic events (OAEs) were major perturbations of the Earth system, associated with high CO2 concentrations in the oceans and atmosphere, high temperatures, and widespread organic-carbon burial. Models for explaining OAEs and other similar phenomena in Earth history make specific predictions about the role and pattern of temperature change, which can be tested through comparison with the geological record. Oceanic Anoxic Event 2 (OAE 2) occurred ~94 m.y. ago and is commonly considered as the type example of an OAE. [...]"

Source: Geology 
Authors: Stuart A. Robinson et al.
DOI: 10.1130/G45842.1

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Evolving paradigms in biological carbon cycling in the ocean

Abstract.

"Carbon is a keystone element in global biogeochemical cycles. It plays a fundamental role in biotic and abiotic processes in the ocean, which intertwine to mediate the chemistry and redox status of carbon in the ocean and the atmosphere. The interactions between abiotic and biogenic carbon (e.g. CO2, CaCO3, organic matter) in the ocean are complex, and there is a half-century-old enigma about the existence of a huge reservoir of recalcitrant dissolved organic carbon (RDOC) that equates to the magnitude of the pool of atmospheric CO2. The concepts of the biological carbon pump (BCP) and the microbial loop (ML) shaped our understanding of the marine carbon cycle.  [...]"

Source: National Science Review
Authors: Chuanlun Zhang et al.
DOI: 10.1093/nsr/nwy074

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Hypoxic volume is more responsive than hypoxic area to nutrient load reductions in the northern Gulf of Mexico – and it matters to fish and fisheries

Abstract.

"While impacts of low oxygen on marine organisms have been reviewed from physiological and ecological perspectives, relating broad population- and ecosystem-level effects to the areal extent of hypoxia (dissolved oxygen concentration below 64 µM, or 2 mg/l) has proven difficult. We suggest that hypoxic volume is a more appropriate metric compared to hypoxic area because volume better integrates the effects of hypoxia on ecological processes relevant to many marine taxa. [...]"

Source: IOP Science
Authors: Donald Scavia et al.
DOI: 10.1088/1748-9326/aaf938

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Short exposure to oxygen and sulfide alter nitrification, denitrification, and DNRA activity in seasonally hypoxic estuarine sediments

Abstract.

"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
DOI: 10.1093/femsle/fny288

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Study of dissolved oxygen responses to tropical cyclones in the Bay of Bengal based on Argo and satellite observations

Abstract.

"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.
DOI: 10.1016/j.scitotenv.2018.12.384

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Ocean deoxygenation and zooplankton: Very small oxygen differences matter

Abstract.

"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.
DOI: 10.1126/sciadv.aau5180

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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

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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. [...]"

Source: Ecology
Authors: Natalya D. Gallo et al.
DOI: 10.1002/ecy.2539

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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. [...]"

Source: EOS

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