Benthic foraminifera and gromiids from oxygen-depleted environments – survival strategies, biogeochemistry and trophic interactions
"The oceans are losing oxygen (O2), and oxygen minimum zones are expanding due to climate warming (lower O2 solubility) and eutrophication related to agriculture. This trend is challenging for most marine taxa that are not well adapted to O2 depletion. For other taxa this trend might be advantageous because they can withstand low O2 concentrations or thrive under O2-depleted or even anoxic conditions. Benthic foraminifera are a group of protists that include taxa with adaptations to partly extreme environmental conditions. [...]".
Authors: Nicolaas Glock
Partitioning of the denitrification pathway and other nitrite metabolisms within global oxygen deficient zones
"Oxygen deficient zones (ODZs) account for about 30% of total oceanic fixed nitrogen loss via processes including denitrification, a microbially mediated pathway proceeding stepwise from NO3– to N2. This process may be performed entirely by complete denitrifiers capable of all four enzymatic steps, but many organisms possess only partial denitrification pathways, either producing or consuming key intermediates such as the greenhouse gas N2O. Metagenomics and marker gene surveys have revealed a diversity of denitrification genes within ODZs, but whether these genes co-occur within [...]".
Authors: Irene H. Zhang et al.
A well-oxygenated eastern tropical Pacific during the warm Miocene
"The oxygen content of the oceans is susceptible to climate change and has declined in recent decades, with the largest effect in oxygen-deficient zones (ODZs), that is, mid-depth ocean regions with oxygen concentrations <5 μmol kg−1 (ref.). Earth-system-model simulations of climate warming predict that ODZs will expand until at least 2100. The response on timescales of hundreds to thousands of years, however, remains uncertain. Here we investigate changes in the response of ocean oxygenation during the warmer-than-present Miocene Climatic Optimum (MCO; 17.0–14.8 million years ago (Ma)). [...]".
Authors: Anya V. Hess et al.
A hydrogenotrophic Sulfurimonas is globally abundant in deep-sea oxygen-saturated hydrothermal plumes
"Members of the bacterial genus Sulfurimonas (phylum Campylobacterota) dominate microbial communities in marine redoxclines and are important for sulfur and nitrogen cycling. Here we used metagenomics and metabolic analyses to characterize a Sulfurimonasfrom the Gakkel Ridge in the Central Arctic Ocean and Southwest Indian Ridge, showing that this species is ubiquitous in non-buoyant hydrothermal plumes at Mid Ocean Ridges across the global ocean. One Sulfurimonas species, USulfurimonas pluma, was found to be globally abundant and active in cold (<0−4 °C), oxygen-saturated and hydrogen-rich hydrothermal plumes. [...]".
Authors: Massimiliano Molari et al.
Drivers and Potential Consequences of Observed Extreme Hypoxia Along the Canadian Pacific Continental Shelf
"Bottom waters of the northeast Pacific continental shelf naturally experience localized hypoxic conditions, with significant influences on food webs and biogeochemical cycling. In August 2021, extreme hypoxia was detected from several measurement platforms along the southern British Columbia continental shelf, with oxygen concentration <60 μmol kg−1, and a difference from the seasonal climatology of more than 2 standard deviations. Early and intense remote upwelling and local density shifts were associated with an anomalously strong spring phytoplankton bloom, which likely stimulated localized respiration of subsurface organic matter. [...]".
Source: Wiley Online Library
Authors: Ana C. Franco et al.
Global ocean redox changes before and during the Toarcian Oceanic Anoxic Event
"Mesozoic oceanic anoxic events are recognized as widespread deposits of marine organic-rich mudrocks temporally associated with mass extinctions and large igneous province emplacement. The Toarcian Oceanic Anoxic Event is one example during which expanded ocean anoxia is hypothesized in response to environmental perturbations associated with emplacement of the Karoo–Ferrar igneous province. However, the global extent of total seafloor anoxia and the relative extent of euxinic (anoxic and sulfide-rich) and non-euxinic anoxic conditions during the Toarcian Oceanic Anoxic Event are poorly constrained. [...]".
Authors: Alexandra Kunert & Brian Kendall
Sedimentary molybdenum and uranium: Improving proxies for deoxygenation in coastal depositional environments
"Sedimentary molybdenum (Mo) and uranium (U) enrichments are widely used to reconstruct changes in bottom water oxygen conditions in aquatic environments. Until now, most studies using Mo and U have focused on restricted suboxic-euxinic basins and continental margin oxygen minimum zones (OMZs), leaving mildly reducing and oxic (but eutrophic) coastal depositional environments vastly understudied. Currently, it is unknown: (1) to what extent Mo and U enrichment factors (Mo- and U-EFs) can accurately reconstruct oxygen conditions in coastal sites experiencing mild deoxygenation, and (2) to what degree secondary [...]".
Source: Science Direct
Authors: K. Mareike Paul et al.
Recovery from microplastic-induced marine deoxygenation may take centuries
"Climate change and plastics pollution are dual threats to marine environments. Here we use biogeochemical and microplastic modelling to show that even if there is complete removal of microplastics and cessation of deposition in the oceans in 2022, regional recovery from microplastic-induced remineralization and water column deoxygenation could take hundreds of years for coastal upwelling zones, the North Pacific and Southern Ocean. [...]".
Authors: Karin Kvale & Andreas Oschlies
Geochemical and paleontological evidence of early Cambrian dynamic ocean oxygenation and its implications for organic matter accumulation in mudrocks
"The evolution of global ocean oxygenation during the early Cambrian remains highly controversial, making it difficult to evaluate how environmental triggers play a role in controlling the organic matter (OM) accumulation in black shales. In this study, an integrated approach, including total organic carbon (TOC) content, major and trace element geochemistry, and microscope images, was systematically conducted in a continuous core well that penetrated through the Lower Cambrian Yanjiahe (YJH)–Shuijingtuo (SJT, subdivided into SM Ⅰ, SM Ⅱ, SM Ⅲ, and SM Ⅳ members) successions (∼541-514Ma) at the Three Gorges area [...]".
Source: Science Direct
Authors: Yu Zhang et al.
Iron deposition during recovery from Late Devonian oceanic anoxia: Implications of the geochemistry of the Kawame ferromanganese deposit, Nedamo Belt
"The Late Devonian, during which one of the “Big Five” Phanerozoic mass extinction events occurred, was one of the most important time intervals in Earth history. Nevertheless, the paucity of deep-sea records due to subduction has hampered elucidation of the pelagic environment during the Late Devonian in Panthalassa. However, ancient hydrothermal ferromanganese sediments, which were deposited on the abyssal seafloor and then accreted onto continental margins, are preserved as umber deposits and exposed in accretionary prisms. These sediments can provide key information to characterize the paleo-ocean. [...]".
Source: Science Direct
Authors: Yusuke Kuwahara et al.
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