Water quality measurements in San Francisco Bay by the U.S. Geological Survey, 1969–2015


The U.S. Geological Survey (USGS) maintains a place-based research program in San Francisco Bay (USA) that began in 1969 and continues, providing one of the longest records of water-quality measurements in a North American estuary. Constituents include salinity, temperature, light extinction coefficient, and concentrations of chlorophyll-a, dissolved oxygen, suspended particulate matter, nitrate, nitrite, ammonium, silicate, and phosphate.

Source: Scientific Data
Authors: Tara S. Schraga & James E. Cloern
DOI: 10.1038/sdata.2017.98

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Environmental Research in Macquarie Harbour (Progress Report)

"This report provides an update on the status of dissolved oxygen and benthic conditions in Macquarie Harbour. It follows on from the results reported in the IMAS report released in January 2017 which described the deterioration of benthic and water column conditions in Macquarie Harbour in spring 2016. This report presents the results and preliminary interpretation of oxygen monitoring data up until the end of March 2017, and a repeat survey of benthic communities in January/February 2017. [...]"

Source: The Institute for Marine and Antarctic Studies
Authors: Jeff Ross and Catriona Macleod

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Eutrophication-Driven Deoxygenation in the Coastal Ocean


"Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world’s coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments."

Source: Oceanography Volume 27 (2014)
Authors: Nancy N. Rabalais et al.
DOI: 10.5670/oceanog.2014.21

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Less oxygen in a warmer ocean

"Climate warming should decrease the concentration of dissolved oxygen (O2) in the surface ocean, for a variety of reasons. This trend, predicted on theoretical grounds and by ocean models, has been difficult to detect within the much greater range of natural variability, though. Ito et al. analyzed existing measurements of O2 in the ocean collected from 1958 to 2015, and they report that a widespread negative O2 trend has begun to emerge. Further work will be needed to understand which mechanisms are responsible for the global and regional trends, however.

Geophys. Res. Lett. 10.1002/2017GL073613 (2017)."

Source: Science
Author: H. Jesse Smith
DOI: 10.1126/science.356.6341.919-g

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Light penetration structures the deep acoustic scattering layers in the global ocean


"The deep scattering layer (DSL) is a ubiquitous acoustic signature found across all oceans and arguably the dominant feature structuring the pelagic open ocean ecosystem. It is formed by mesopelagic fishes and pelagic invertebrates. The DSL animals are an important food source for marine megafauna and contribute to the biological carbon pump through the active flux of organic carbon transported in their daily vertical migrations. They occupy depths from 200 to 1000 m at daytime and migrate to a varying degree into surface waters at nighttime. Their daytime depth, which determines the migration amplitude, varies across the global ocean in concert with water mass properties, in particular the oxygen regime, but the causal underpinning of these correlations has been unclear. [...]"

Source: Science Advances
Author: Dag L. Aksnes et al.
DOI: 10.1126/sciadv.1602468

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Spreading Dead Zones and Consequences for Marine Ecosystems


"Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems."

Source: Science Magazine (2008)
Authors: Robert J. Diaz, Rutger Rosenberg
DOI: 10.1126/science.1156401

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Dissolved Oxygen Sensor in Animal-Borne Instruments: An Innovation for Monitoring the Health of Oceans


"The current decline in dissolved oxygen concentration within the oceans is a sensitive indicator of the effect of climate change on marine environment. However the impact of its declining on marine life and ecosystems’ health is still quite unclear because of the difficulty in obtaining in situ data, especially in remote areas, like the Southern Ocean (SO). Southern elephant seals (Mirounga leonina) proved to be a relevant alternative to the traditional oceanographic platforms to measure physical and biogeochemical structure of oceanic regions rarely observed. In this study, we use a new stage of development in biologging technology to draw a picture of dissolved oxygen concentration in the SO. [...]"

Source: PLOS
Authors: Frederic Bailleul, Jade Vacquie-Garcia, Christophe Guinet
DOI: 10.1371/journal.pone.0132681

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Oregon Shelf Hypoxia Modeling


"Bottom hypoxia on the shelf in the Northeast Pacific is caused by different processes than coastal hypoxia related to riverine inputs. Hypoxia off the coast of Oregon is a naturally occurring process as opposed to the anthropogenically forced hypoxia found in many coastal environments (e.g., Gulf of Mexico shelf, Chesapeake Bay). Off Oregon, bottom hypoxia occurs in summers that have large upwelling-driven near-bottom transport of high nitrate, low dissolved oxygen (DO) waters onto the shelf. The combination of low DO and high nitrate provides initially low (but not hypoxic) DO conditions near the bottom, and nitrate fertilization of shelf surface waters, leading to substantial phytoplankton production. [...]"

Source: Modeling Coastal Hypoxia (pp 215-238)
Authors: Andrey O. Koch, Yvette H. Spitz, Harold P. Batchelder
DOI: 10.1007/978-3-319-54571-4_9

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Influence of dissolved oxygen on the protectiveness and morphological characteristics of calcareous deposits with galvanostatic polarization


"The influence of dissolved oxygen on calcareous deposits formed under galvanostatic polarization mode was studied. When the dissolved oxygen concentration was less than 7 mg L−1, the cathodic protection potential showed a plateau at the initial polarization, and then quickly shifted negatively. While the dissolved oxygen was more than 9 mg L−1, the potential shifted negatively in a linear form. After 168 h of polarization, the final protection potential shifted negatively with the decreasing dissolved oxygen concentration.  The deposition progress was monitored by electrochemical impedance spectroscopy, and only one single loop was found in Nyquist diagram, indicating deposits of ineffective protectiveness precipitation under the experimental conditions. [...]"


Source: Journal of Ocean University of China
Authors: Chengjie Li, Min Du, Rongjie Gao
DOI: 10.1007/s11802-017-2933-4

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Upper Ocean O2 trends: 1958-2015


"Historic observations of dissolved oxygen (O2) in the ocean are analyzed to quantify multi-decadal trends and variability from 1958 to 2015. Additional quality control is applied and the resultant oxygen anomaly field is used to quantify upper ocean O2 trends at global and hemispheric scales. A widespread negative O2 trend is beginning to emerge from the envelope of interannual variability. Ocean reanalysis data is used to evaluate relationships with changes in ocean heat content (OHC) and oxygen solubility (O2,sat). Global O2 decline is evident after the 1980s, accompanied by an increase in global OHC. [...]"


Source: Geophysical Reasearch Letters
Authors: Takamitsu Ito et al.
DOI: 10.1002/2017gl073613

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