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Constraints on Early Paleozoic deep-ocean oxygen concentrations from the iron geochemistry of the Bay of Islands ophiolite

Abstract. 

"The deep ocean is generally considered to have changed from anoxic in the Precambrian to oxygenated by the Late Paleozoic (∼420–400 Ma) due to changes in atmospheric oxygen concentrations. When the transition occurred, that is, in the Early Paleozoic or not until the Late Paleozoic, is less well constrained. To address this, we measured Fe3+/ΣFe of volcanic rocks, sheeted dykes, gabbros, and ultramafic rocks from the Early Paleozoic (∼485 Ma) Bay of Islands (BOI) ophiolite as a proxy for hydrothermal alteration in the presence or absence of O2 derived from deep marine fluids. [...]".

 

Source: Geochemistry, Geophysics, Geosystems 
Authors: Daniel A. Stolper et al. 
DOI: https://doi.org/10.1029/2021GC010196

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Deglacial restructuring of the Eastern equatorial Pacific oxygen minimum zone

Abstract. 

"Oxygenation in the Eastern Equatorial Pacific is responsive to ongoing climate change in the modern ocean, although whether the region saw a deglacial change in extent or position of the Oxygen Minimum Zone remains poorly constrained. Here, stable isotopes from the shells of an Oxygen Minimum Zone-dwelling planktic foraminifer are used to reassess the position of the mid-water Oxygen Minimum Zone relative to both the thermocline and benthos. Oxygen isotopes record a rapid shoaling of the Oxygen Minimum Zone towards the thermocline associated with Heinrich Stadial 1 and persisting through the deglaciation. [...]". 

 

Source: Communications Earth & Environment
Authors: Catherine V. Davis
DOI: https://doi.org/10.1038/s43247-022-00477-8

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Linkage of the late Cambrian microbe-metazoan transition (MMT) to shallow-marine oxygenation during the SPICE event

Abstract.

"Microbe-metazoan transitions (MMTs), representing a switch from microbe-mediated to metazoan-mediated carbonate production, have been linked to major changes in Earth-surface conditions. The ‘late Cambrian MMT’ (nomen novum), during which microbial reefs were replaced by maceriate and lithistid sponge reefs, coincided with a sharp rise in atmospheric O2 levels attributed to the Steptoean Positive Carbon Isotope Excursion (SPICE) at ~497–494 Ma. However, relationships between atmospheric oxygenation, marine redox conditions, and the MMT have not been thoroughly investigated to date. [...]". 

 

Source: Science Direct 
Authors: Lei Zhang et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103798

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Reactive oxygen species in the world ocean and their impacts on marine ecosystems

Abstract. 

"Reactive oxygen species (ROS) are omnipresent in the ocean, originating from both biological (e.g., unbalanced metabolism or stress) and non-biological processes (e.g. photooxidation of colored dissolved organic matter). ROS can directly affect the growth of marine organisms, and can also influence marine biogeochemistry, thus indirectly impacting the availability of nutrients and food sources. Microbial communities and evolution are shaped by marine ROS, and in turn microorganisms influence steady-state ROS concentrations by acting as the predominant sink for marine ROS. [...]".

 

Source: Science Direct 
Authors: J. Jeffrey Morris et al.
DOI: https://doi.org/10.1016/j.redox.2022.102285

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Job offer: Postdoctoral researcher in Ocean Biogeochemistry

Job offer.

"The High Meadows Environmental Institute at Princeton University is seeking a Postdoctoral research associate or more senior researcher in the area of ocean biophysical modeling to work with Professor Laure Resplandy. The researcher will investigate the impact of climate change and human perturbations on ocean oxygenation and coastal hypoxia. The researcher will specifically examine how riverine nutrient loadings and aerosol deposition control oxygen levels and how the risk of coastal hypoxia, which is crucial for ecosystem and ecosystem services, will evolve in the future. The position is funded by an NSF CAREER grant (Award # 2042672).

The ideal candidate will have a strong background in numerical modeling, but candidates with the necessary background in geophysical fluid dynamics and/or ocean biogeochemistry will be given full consideration. A Ph.D. in Geosciences or related field is required. The position is available for one year, with a possibility for renewal contingent upon satisfactory performance and funding. Postdoctoral appointments are initially for one year with the renewal for subsequent years based on satisfactory performance and continued funding. A competitive salary is offered commensurate with experience and qualifications.

Applicants should apply online to https://www.princeton.edu/acad-positions/position/24941." 


Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

Abstract. 

"We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). [...]". 

 

Source: Science Direct 
Authors: Carlos A. Alvarez Zarikian et al.
DOI: https://doi.org/10.1016/j.marmicro.2022.102105

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Biotic induction and microbial ecological dynamics of Oceanic Anoxic Event 2

Abstract. 

"Understanding the causal mechanisms of past marine deoxygenation is critical to predicting the long-term Earth systems response to climate change. However, the processes and events preceding widespread carbon burial coincident with oceanic anoxic events remain poorly constrained. Here, we report a comprehensive biomarker inventory enveloping Oceanic Anoxic Event 2 that captures microbial communities spanning epipelagic to benthic environments in the southern proto-North Atlantic Ocean. We identify an abrupt, sustained increase in primary productivity that predates Oceanic Anoxic Event 2 by ∼220 ± 4 thousand years, well before other geochemical proxies register biogeochemical perturbations. [...]". 

 

Source: Communications Earth & Environment 
Authors: Gregory T. Connock et al. 
DOI: https://doi.org/10.1038/s43247-022-00466-x 

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Oceanic anoxia and extinction in the latest Ordovician

Abstract.

"The Late Ordovician (Hirnantian) mass extinction (LOME) was marked by two discrete pulses of high species turnover rates attributed to glacial cooling (LOME-1) and subsequent expansion of anoxic marine conditions (LOME-2). However, the mechanisms and extent of global marine anoxia remain controversial. In this study, we present uranium isotope (U) data from a new Ordovician-Silurian (O-S) boundary carbonate section in the Southwest China to explore the extent/duration of the global marine anoxia, and links to the LOME. [...]". 

 

Source: Science Direct 
Authors: Mu Liu et al.
DOI: https://doi.org/10.1016/j.epsl.2022.117553

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On anomalously high sub-surface dissolved oxygen in the Indian sector of the Southern Ocean

Abstract.

"The Southern Ocean (SO) plays a critical role in global ocean productivity and carbon cycling. Bio-Argo floats deployed in the Indian sector of the Southern Ocean provides new insights into the biogeochemical processes. Here we report significantly higher dissolved oxygen (DO) (~ 310 μmol/kg) in summer of 2014–2015 for one float (F1) and winter of 2014 in other float (F2) at sub-surface layer in the subantarctic region of the SO. The summer DO peak in F1 was 10% higher than those during the summer of succeeding year, while the winter DO peak in F2 was 20% higher than those during the winter of succeeding year. [...]".

 

Source: Journal of Oceanography 
Authors: Prince Prakash et al.
DOI: https://doi.org/10.1007/s10872-022-00644-7 

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Coastlines at Risk of Hypoxia From Natural Variability in the Northern Indian Ocean

Abstract. 

"Coastal hypoxia—harmfully low levels of oxygen—is a mounting problem that jeopardizes coastal ecosystems and economies. The northern Indian Ocean is particularly susceptible due to human-induced impacts, vast naturally occurring oxygen minimum zones, and strong variability associated with the seasonal monsoons and interannual Indian Ocean Dipole (IOD). We assess how natural factors influence the risk of coastal hypoxia by combining a large set of oxygen measurements with satellite observations to examine how the IOD amplifies or suppresses seasonal hypoxia tied to the Asian Monsoon. We show that on both seasonal and interannual timescales hypoxia is controlled by wind- and coastal Kelvin wave-driven upwelling of oxygen-poor waters onto the continental shelf and reinforcing biological feedbacks (increased subsurface oxygen demand). [...]".

 

Source: Global Biogeochemical Cycles
Authors: Jenna Pearson et al.
DOI: https://doi.org/10.1029/2021GB007192

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