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Deep‐sea oxygen depletion and ocean carbon sequestration during the last ice age

Abstract.

"Enhanced ocean carbon storage during the Pleistocene ice ages lowered atmospheric CO2 concentrations by 80 to 100 ppm relative to interglacial levels. Leading hypotheses to explain this phenomenon invoke a greater efficiency of the ocean's biological pump, in which case carbon storage in the deep sea would have been accompanied by a corresponding reduction in dissolved oxygen. We exploit the sensitivity of organic matter preservation in marine sediments to bottom water oxygen concentration to constrain the level of dissolved oxygen in the deep central equatorial Pacific Ocean during the last glacial period (18,000 – 28,000 years BP) to have been within the range of 20‐50 μmol/kg, much less than modern value of ca. 168 μmol/kg. [...]"

Source: Global Biogeochemical Cycles
Authors: Robert F. Anderson et al.
DOI: 10.1029/2018GB006049

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Consequences of climate-induced low oxygen conditions for commercially important fish

Abstract.

"Oxygen availability is key in determining habitat suitability for marine fish. As a result of climate change, low oxygen conditions are predicted to occur more frequently and over a greater geographic extent. Studies assessing the long-term chronic effects and impacts for commercially important fish are rare. To assess the potential effects of climate-induced low oxygen on fisheries, physiological data, such as critical thresholds, derived from laboratory experiments on 5 commercial fish species were integrated with hindcast and future oxygen projections from the hydrodynamic-biogeochemical model GETM-ERSEM. [...]"

Source: Marine Ecology Progress Series (2017)
Authors: Bryony L. Townhill et al.
DOI: 10.3354/meps12291

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Asymmetric dynamical ocean responses in warming icehouse and cooling greenhouse climates

Abstract.

"Warm periods in Earth's history tend to cool more slowly than cool periods warm. Here we explore initial differences in how the global ocean takes up and gives up heat and carbon in forced rapid warming and cooling climate scenarios. We force an intermediate-complexity earth system model using two atmospheric CO2 scenarios. A ramp-up (1% per year increase in atmospheric CO2 for 150 years) starts from an average global CO2 concentration of 285 ppm to represent warming of an icehouse climate. [...]"

Source: Environmental Research Letters
Authors: Karin F. Kvale et al.
DOI: 10.1088/1748-9326/aaedc3

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Unexpectedly high diversity of anammox bacteria detected in deep-sea surface sediments of the South China Sea

Abstract.

"Ca. Scalindua is an exclusive genus of anammox bacteria known to exhibit low diversity found in deep-sea ecosystems. In this study, the community composition of anammox bacteria in surface sediments of the South China Sea (SCS) was analyzed using high-throughput sequencing techniques. Results indicated that the dominant OTUs were related to three different genera of anammox bacteria, identified as Ca. Scalindua (87.29%), Ca. Brocadia (10.27%) and Ca. Kuenenia (2.44%), in order of decreasing abundance. [...]"

Source: FEMS Microbiology Ecology
Authors: Jiapeng Wu et al.
DOI: 10.1093/femsec/fiz013

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Rates and pathways of N2 production in a persistently anoxic fjord: Saanich Inlet, British Columbia

Abstract.

"Marine oxygen minimum zones (OMZs) support 30-50% of global fixed-nitrogen (N) loss but comprise only 7% of total ocean volume. This N-loss is driven by canonical denitrification and anaerobic ammonium oxidation (anammox), and the distribution and activity of these two processes vary greatly in space and time. Factors that regulate N-loss processes are complex, including organic matter availability, oxygen concentrations, and NO2- and NH4+ concentrations. [,,,]"

Source: Frontiers in Marine Science
Authors: Céline C. Michiels et al.
DOI: 10.3389/fmars.2019.00027

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Mid-Holocene deepening of the Southeast Pacific oxycline

Abstract.

"This study presents new high resolution sedimentary δ15N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high sedimentation rate allowing interpretations at millennial to centennial timescale. [...]"

Source: Global and Planetary Change
Authors: Elfi Mollier-Vogel et al.
DOI: 10.1016/j.gloplacha.2018.10.020

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Effects of Higher CO2 and Temperature on Exopolymer Particle Content and Physical Properties of Marine Aggregates

Abstract.

"We investigated how future ocean conditions, and specifically the interaction between temperature and CO2, might affect marine aggregate formation and physical properties. Initially, mesocosms filled with coastal seawater were subjected to three different treatments of CO2 concentration and temperature: (1) 750 ppm CO2, 16°C, (2) 750 ppm CO2, 20°C, and (3) 390 ppm CO2, 16°C. Diatom-dominated phytoplankton blooms were induced in the mesocosms by addition of nutrients. [...]"

Source: Frontiers in Marine Science
Authors: Carolina Cisternas-Novoa et al.
DOI: 10.3389/fmars.2018.00500

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Isotopic fingerprints of benthic nitrogen cycling in the Peruvian oxygen minimum zone

Abstract.

"Stable isotopes (15,14N, 18,16O) of dissolved inorganic nitrogen (N) were measured in sediment porewaters and benthic flux chambers across the Peruvian oxygen minimum zone (OMZ) from 74 to 1000 m water depth. Sediments at all locations were net consumers of bottom water NO3−. In waters shallower than 400 m, this sink was largely attributed to dissimilatory nitrate reduction to ammonium (DNRA) by filamentous nitrate-storing bacteria (Marithioploca and Beggiatoa) and to denitrification by foraminifera. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: A.W.Dale et al.
DOI: 10.1016/j.gca.2018.10.025

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‘Stop treating seas as a sewer,’ MPs urge in bid for protection treaty

"A new global agreement to protect the seas should be a priority for the government to stop our seas becoming a “sewer”, according to a cross-party group of MPs.

Plastic pollution is set to treble in the next decade, the environmental audit committee warned, while overfishing is denuding vital marine habitats of fish, and climate change is causing harmful warming of the oceans as well as deoxygenation and acidification. [...]"

Source: The Guardian

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UK must support ‘Paris agreement for the sea’ to protect global oceans, say MPs

"British seas are being treated “like a sewer”, polluted by an endless stream of plastics, untreated waste and farming effluent, MPs have warned. In a damning new report, the Environmental Audit Committee has laid out the dangers facing the nation’s oceans and what needs to be done to address them.

Besides pollution, climate change, overfishing and deep sea mining are all threatening marine ecosystems and the trillions of pounds they deliver to the economy, the report states. [...]"

Source: Independent

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