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Microbial niches in marine oxygen minimum zones

Abstract.

"In the ocean’s major oxygen minimum zones (OMZs), oxygen is effectively absent from sea water and life is dominated by microorganisms that use chemicals other than oxygen for respiration. Recent studies that combine advanced genomic and chemical detection methods are delineating the different metabolic niches that microorganisms can occupy in OMZs. Understanding these niches, the microorganisms that inhabit them, and their influence on marine biogeochemical cycles is crucial as OMZs expand with increasing seawater temperatures."

Source: Nature Reviews Microbiology
Authors: Anthony D. Bertagnolli & Frank J. Stewart
DOI: 10.1038/s41579-018-0087-z

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Lipids as indicators of nitrogen cycling in present and past anoxic oceans

Summary.

"Nitrogen (N) cycling influences primary production in the ocean and, hence, the global climate. It is performed by a variety of microorganisms, including eukaryotes, bacteria and archaea in oxic, suboxic, and anoxic waters. Our knowledge of the reactions involved in marine N cycling and its associated microorganisms has greatly increased in the last decade due to the development of multiple culture-independent methods. Among them are gene and lipid biomarkers, which hold taxonomic potential and can be successfully applied in modern day and paleoenvironmental studies. However, many aspects of N cycling and their long-term implications for the marine environment and the global climate still require more study, especially in suboxic and anoxic waters, including the oxygen-deficient zones (ODZs), which are expanding in the modern oceans.

Author: Martina Sollai

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Identifying oxygen minimum zone-type biogeochemical cycling in Earth history using inorganic geochemical proxies

Abstract.

"Because of anthropogenic global warming, the world ocean is currently losing oxygen. This trend called ocean deoxygenation is particularly pronounced in low-latitude upwelling-related oxygen minimum zones (OMZs). In these areas, the temperature-related oxygen drawdown is additionally modulated by biogeochemical feedback mechanisms between sedimentary iron (Fe) and phosphorus release, water column nitrogen cycling and primary productivity. Similar feedbacks were likely active during past periods of global warming and oceandeoxygenation. However, their integrated role in amplifying or mitigating climate change-driven ocean anoxia has not been evaluated in a systematic fashion. [...]"

Source: Earth-Science Reviews
Author: Florian Scholz
DOI: 10.1016/j.earscirev.2018.08.002

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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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A Novel Eukaryotic Denitrification Pathway in Foraminifera

Abstract.

"Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats, where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. [...]"

Source: Current Biology
Authors: Christian Woehle et al.
DOI: 10.1016/j.cub.2018.06.027

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How nutrients are removed in oxygen-depleted regions of the ocean

"In the course of global climate change, scientists are observing the increase of low-oxygen areas in the ocean, also termed oxygen minimum zones (OMZs). Large-scale OMZs exist, for example, in the Pacific off the coast of South America or in the Indian Ocean. Since little to no oxygen is present in these regions - depending on the depth of the water - organisms whose metabolisms is independent of oxygen have a distinct advantage. These organisms include some representatives of the foraminifera: unicellular, shell-forming microorganisms, which have a nucleus and thus belong to the eukaryotes. Their life style involves a particular metabolic pathway termed anaerobic respiration. In the absence of oxygen, they convert nitrate present in the water into molecular nitrogen. [...]"

Source: Kiel University

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Macrobenthic communities in a shallow normoxia to hypoxia gradient in the Humboldt upwelling ecosystem

Abstract.

"Hypoxia is one of the most important stressors affecting the health conditions of coastal ecosystems. In highly productive ecosystems such as the Humboldt Current ecosystem, the oxygen minimum zone is an important abiotic factor modulating the structure of benthic communities over the continental shelf. Herein, we study soft-bottom macrobenthic communities along a depth gradient–at 10, 20, 30 and 50 m–for two years to understand how hypoxia affects the structure of shallow communities at two sites in Mejillones Bay (23°S) in northern Chile. [...]"

Source: PLoS ONE
Authors: Maritza Fajardo et al.
DOI: 10.1371/journal.pone.0200349

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Oxygen minimum zones in the early Cambrian ocean

Abstract.

"The relationship between the evolution of early animal communities and oceanic oxygen levels remains unclear. In particular, uncertainty persists in reconstructions of redox conditions during the pivotal early Cambrian (541-510 million years ago, Ma), where conflicting datasets from deeper marine settings suggest either ocean anoxia or fully oxygenated conditions. By coupling geochemical palaeoredox proxies with a record of organic-walled fossils from exceptionally well-defined successions of the early Cambrian Baltic Basin, we provide evidence for the early establishment of modern-type oxygen minimum zones (OMZs). [...]"

Source: Geochemical Perspectives Letters 
Authors: R. Guilbaud et al.
DOI: 10.7185/geochemlet.1806

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Chesapeake Bay: Larger-than-average summer 'dead zone' forecast for 2018 after wet spring

"Ecologists from the University of Michigan and the University of Maryland Center for Environmental Science are forecasting a larger-than-average Chesapeake Bay "dead zone" in 2018, due to increased rainfall in the watershed this spring.
 

This summer's Chesapeake Bay hypoxic or dead zone, an area of low to no oxygen that can kill fish and other aquatic life, is expected to be about 1.9 cubic miles (7.9 cubic kilometers), according to the forecast released today by the two universities. [...]"

Source: Phys.org

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