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A Novel Approach for Measuring the Gulf of Mexico Dead Zone: Toward Better Temporal and Spatial Estimates for Management Applications

Abstract.

"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.
DOI: 10.1021/acs.est.8b03474

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What could cause the Mississippi Bight to become hypoxic?

"Coastal regions with low dissolved oxygen (known as hypoxia) can lead to poor water quality and harm regional fisheries. These areas of low dissolved oxygen are expanding and expected to continue growing in coming years due to human impacts on the environment.

A recent article published in Continental Shelf Research explores aspects of the environmental conditions that can potentially lead to hypoxia in the Mississippi Bight region of the northern Gulf of Mexico. This area extends from Apalachicola in Florida to the Mississippi River Delta. [...]"

Source:  EurekAlert!

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Tracking sea surface salinity and dissolved oxygen on a river-influenced, seasonally stratified shelf, Mississippi Bight, northern Gulf of Mexico

Abstract.

"River discharge, and its resulting region of freshwater influence (ROFI) in the coastal ocean, has a critical influence on physical and biogeochemical processes in seasonally stratified shelf ecosystems. Multi-year (2010–2016) observations of satellite-derived sea surface salinity (SSS) and in situ water column hydrographic data during summer 2016 were used to investigate physical aspects of the ROFI east of the Mississippi River Delta to better assess regional susceptibility to hypoxia in the summer months. [...]"

Source: Continental Shelf Research
Authors: Brian Dzwonkowski et al.
DOI: 10.1016/j.csr.2018.09.009

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Glacial expansion of oxygen-depleted seawater in the eastern tropical Pacific

Abstract.

"Increased storage of carbon in the oceans has been proposed as a mechanism to explain lower concentrations of atmospheric carbon dioxide during ice ages; however, unequivocal signatures of this storage have not been found. In seawater, the dissolved gases oxygen and carbon dioxide are linked via the production and decay of organic material, with reconstructions of low oxygen concentrations in the past indicating an increase in biologically mediated carbon storage. [...]"

Source: Nature
Authors: Babette A. A. Hoogakker et al.
DOI: 10.1038/s41586-018-0589-x

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Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru

Abstract.

"The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. [...]"

Source: Biogeosciences
Authors: Marine Bretagnon et al.
DOI: 10.5194/bg-15-5093-2018

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H2S events in the Peruvian oxygen minimum zone facilitate enhanced dissolved Fe concentrations

Abstract.

"Dissolved iron (DFe) concentrations in oxygen minimum zones (OMZs) of Eastern Boundary Upwelling Systems are enhanced as a result of high supply rates from anoxic sediments. However, pronounced variations in DFe concentrations in anoxic coastal waters of the Peruvian OMZ indicate that there are factors in addition to dissolved oxygen concentrations (O2) that control Fe cycling. [...]"

Source: Scientific Reports
Authors: Christian Schlosser et al. 
DOI: 10.1038/s41598-018-30580-w

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The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings...

...in a general circulation model

Abstract.

"The complexity of dissolved gas cycling in the ocean presents a challenge for mechanistic understanding and can hinder model intercomparison. One helpful approach is the conceptualization of dissolved gases as the sum of multiple, strictly defined components. Here we decompose dissolved inorganic carbon (DIC) into four components: saturation (DICsat), disequilibrium (DICdis), carbonate (DICcarb), and soft tissue (DICsoft). The cycling of dissolved oxygen is simpler, but can still be aided by considering O2, O2sat, and O2dis. [...]"

Source: Biogeosciences
Authors: Sarah Eggleston and Eric D. Galbraith
DOI: 10.5194/bg-15-3761-2018

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Ventilation of oxygen to oxygen minimum zone due to anticyclonic eddies in the Bay of Bengal

Abstract.

"Intense oxygen minimum zone (OMZ) occurs in the mid‐depth of the Eastern Tropical Pacific (ETP), Arabian Sea (AS), and Bay of Bengal (BoB). However, the occurrence of anammox/denitrification was reported only in the ETP and AS and its absence in the BoB is attributed to presence of traces of dissolved oxygen (DO). Anticyclonic Eddies (ACE) supply high nutrient, organic‐rich and oxygen poor waters from the coastal upwelling regions leading to strengthening of OMZ in the offshore of AS and ETP.  [...]"

Source: Biogeosciences
Authors: V. V. S. S. Sarma, T. V. S. Udaya Bhaskar
DOI: 10.1029/2018JG004447

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Reversal of Increasing Tropical Ocean Hypoxia Trends With Sustained Climate Warming

Abstract.

"Dissolved oxygen (O2) is essential for the survival of marine animals. Climate change impacts on future oxygen distributions could modify species biogeography, trophic interactions, biodiversity, and biogeochemistry. The Coupled Model Intercomparison Project Phase 5 models predict a decreasing trend in marine O2 over the 21st century.  [...]"

Source: Global Biogeochemical Cycles
Authors: Weiwei Fu et al.
DOI: 10.1002/2017GB005788

 Read the full article here.


A Sixteen-year Decline in Dissolved Oxygen in the Central California Current

Abstract.

"A potential consequence of climate change is global decrease in dissolved oxygen at depth in the oceans due to changes in the balance of ventilation, mixing, respiration, and photosynthesis. We present hydrographic cruise observations of declining dissolved oxygen collected along CalCOFI Line 66.7 (Line 67) off of Monterey Bay, in the Central California Current region, and investigate likely mechanisms.  [...]"

Source: Scientific Reports
Authors: Alice S. Ren et al.
DOI: 10.1038/s41598-018-25341-8

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