Physical controls on oxygen distribution and denitrification potential in the north west Arabian Sea


"At suboxic oxygen concentrations, key biogeochemical cycles change and denitrification becomes the dominant remineralization pathway. Earth system models predict oxygen loss across most ocean basins in the next century; oxygen minimum zones near suboxia may become suboxic and therefore denitrifying. Using an ocean glider survey and historical data, we show oxygen loss in the Gulf of Oman (from 6‐12 to < 2 μmol kg‐1) not represented in climatologies. [...]"

Source: Grophysical Research Letters
Authors: B. Y. Queste et al.
DOI: 10.1029/2017GL076666

Read the full article here.

Growing 'dead zone' confirmed by underwater robots in the Gulf of Oman

"New research reveals a growing 'dead zone' in the Gulf of Oman. Little data has been collected in the area for almost 50 years because of piracy and geopolitical tensions. The area devoid of oxygen was confirmed by underwater robots. Reasearchers found an area larger than Scotland with almost no oxygen left. The environmental disaster is worse than expected with dire consequences for fish and marine plants, plus humans who rely on the oceans for food and employment. "

Source: Science Daily

Read the full article here.

Nancy Rabalais - The "dead zone" of the Gulf of Mexico

"Ocean expert Nancy Rabalais tracks the ominously named "dead zone" in the Gulf of Mexico -- where there isn't enough oxygen in the water to support life. The Gulf has the second largest dead zone in the world; on top of killing fish and crustaceans, it's also killing fisheries in these waters. Rabalais tells us about what's causing it -- and how we can reverse its harmful effects and restore one of America's natural treasures."

Watch the full TED Talk here.

Deglacial upwelling, productivity and CO2 outgassing in the North Pacific Ocean


"The interplay between ocean circulation and biological productivity affects atmospheric CO2 levels and marine oxygen concentrations. During the warming of the last deglaciation, the North Pacific experienced a peak in productivity and widespread hypoxia, with changes in circulation, iron supply and light limitation all proposed as potential drivers. [...]"

Source: Nature Geoscience
Authors: William R. Gray et al.
DOI: 10.1038/s41561-018-0108-6

Read the full article here.

Oxygenation of the Mesoproterozoic ocean and the evolution of complex eukaryotes


"The Mesoproterozoic era (1,600–1,000 million years ago (Ma)) has long been considered a period of relative environmental stasis, with persistently low levels of atmospheric oxygen. There remains much uncertainty, however, over the evolution of ocean chemistry during this period, which may have been of profound significance for the early evolution of eukaryotic life. [...]"

Source: Nature Geoscience
Authors: Kan Zhang
DOI: 10.1038/s41561-018-0111-y

Read the full article here.

Tiny microenvironments in the ocean hold clues to global nitrogen cycle

"Nitrogen is essential to marine life and cycles throughout the ocean in a delicately balanced system. Living organisms--especially marine plants called phytoplankton--require nitrogen in processes such as photosynthesis. In turn, phytoplankton growth takes up carbon dioxide from the atmosphere and helps regulate global climate. [...]"

Source: EruekAlert

Read the full article here.


Life on the edge: active microbial communities in the Kryos MgCl2-brine basin at very low water activity


"The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl2-equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. [...]"

Source: The ISME Journal
Authors: Lea Steinle et al.
DOI: 10.1038/s41396-018-0107-z

Read the full article here.

Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction


"Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. [...]"

Source: Science Advances
Authors: Feifei Zhan et al.

Read the full article here.

Ocean euxinia and climate change "double whammy" drove the Late Ordovician mass extinction


"The Late Ordovician mass extinction (LOME, ca. 445 Ma) was the first of the "Big Five" Phanerozoic extinction events and comprised two extinction pulses. Proposed kill mechanisms include glacially induced global cooling and the expansion of water-column anoxia and/or euxinia (sulfidic conditions), but no general consensus has been reached with regard to the precise role of these mechanisms. [...]"

Source: Geology
Authors: Caineng Zou et al.
DOI: 10.1130/G40121.1

Read the full article here.

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia


"Emerging geochemical evidence suggests that the atmosphere-ocean system underwent a significant decrease in O2 content following the Great Oxidation Event (GOE), leading to a mid-Proterozoic ocean (ca. 2.0–0.8 Ga) with oxygenated surface waters and predominantly anoxic deep waters. The extent of mid-Proterozoic seafloor anoxia has been recently estimated using mass-balance models based on molybdenum (Mo), uranium (U), and chromium (Cr) enrichments in organic-rich mudrocks (ORM).  [...]"

Source: Geochimica et Cosmochimica Acta
Authors: Alex I.Sheen et al.
DOI: 10.1016/j.gca.2018.01.036

Read the full article here.

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