Abstract.

"Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. [...]".

Source: Science Direct 
Authors: Emma R. Haxen et al.
DOI: https://doi.org/10.1016/j.epsl.2023.118416

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Abstract.

"Marine biodiversity increased markedly during the Ordovician Period (~487–443 million years ago). Some intervals within the Ordovician were associated with unusually rapid and prominent rises in taxonomic richness, the reasons for which remain debated. Links between increased oxygenation and biodiversification have been proposed, although supporting marine oxygen proxy data are limited. Here we present an expansive multi-site iodine-to-calcium (I/Ca) record from Lower–Middle Ordovician marine carbonates in Baltoscandia that provides a detailed account of the spatio-temporal development of oxygen conditions across this palaeoshelf. [...]".

Source: Nature
Authors: Anders Lindskog et al.
DOI: https://doi.org/10.1038/s41561-023-01287-z

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Abstract.

"The largest negative inorganic carbon isotope excursion in Earth’s history, namely the Ediacaran Shuram Excursion (SE), closely followed by early animal radiation, has been widely interpreted as a consequence of oceanic oxidation. However, the primary nature of the signature, source of oxidants, and tempo of the event remain contested. Here, we show that carbonate-associated sulfate (CAS) from three different paleocontinents all have conspicuous negative 17O anomalies (Δ′17OCAS values down to −0.53‰) during the SE. [...]".

Source: Nature
Authors: Haiyang Wang et al.
DOI: https://doi.org/10.1038/s41467-023-39962-9

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Abstract.

"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)). [...]".

Source: Nature
Authors: Anya V. Hess et al.
DOI: https://doi.org/10.1038/s41586-023-06104-6

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Abstract. 

"The exchange of water masses between deep fjords and the open ocean is commonly constrained by a topographical barrier called the sill. While fjord water above the sill depth communicates relatively freely with the open ocean, water below the sill depth is caught inside the fjord basin. This basin water may remain stagnant in deep fjords for many successive years. During these periods, the biological consumption of dissolved oxygen is larger than the supply of new oxygen, and the fjord basin might experience hypoxia and even anoxia. [...]".

Source: Science Direct
Authors: Dag L. Aksnes et al.
DOI: https://doi.org/10.1016/j.ecss.2023.108286 

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Abstract. 

"Deep-sea oxygen concentrations reflect combined effects of air-sea exchange in high-latitude surface waters, ventilation through ocean circulation and the organic carbonremineralization at depth. Reconstruction of past bottom water oxygen (BWO) concentrations has been challenging due to limitations of each existing BWO proxy whose fidelity may be complicated by diagenetic or depositional factors. Therefore, evaluations on BWO changes with multi-proxy approach are always preferred. In this study, we exploit the authigenic uranium content on mixed planktonic foraminiferal coatings as a BWO proxy by presenting new foraminiferal [...]".

Source: Science Direct
Authors: Rong Hu et al.
DOI: https://doi.org/10.1016/j.quascirev.2023.108028

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Abstract. 

"The Mo isotope composition of late Ediacaran global seawater and the global extent of ocean oxygenation are still debated due to the complex controls on sedimentary Mo isotope compositions and the rarity with which sediments directly capture global seawater Mo isotope compositions. Deep-water sulfidic sediments from modern severely restricted basins like the Black Sea have the best chance of capturing global seawater Mo isotope compositions. However, few studies have focused on sedimentary Mo isotope variations and their causes in late Ediacaran restricted basins. [...]". 

Source: Science Direct
Authors: Zhaozhao Tan et al.
DOI: https://doi.org/10.1016/j.chemgeo.2023.121410

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Abstract. 

"Photosynthesis produces molecular oxygen, but it is the burial of organic carbon in sediments that has allowed this O2 to accumulate in Earth’s atmosphere. Yet many direct controls on the preservation and burial of organic carbon have not been explored in detail. For modern Earth, it is known that reactive iron phases are important for organic carbon preservation, suggesting that the availability of particulate iron could be an important factor for the oxygenation of the oceans and atmosphere over Earth history. Here we develop a theoretical model to investigate the effect of mineral–organic preservation on the oxygenation of the Earth, supported by a proxy [...]".

Source: Nature 
Authors: Mingyu Zhao et al.
DOI: https://doi.org/10.1038/s41561-023-01133-2

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Abstract. 

"The Rare Earth Element (REE) systematics of the post-Marinoan cap dolostones reflect the marine redox conditions and chemistry in the immediate aftermath of the snowball Earth. Rare earth elements and yttrium (REY) compositions in the Doushantuo cap dolostones that directly overlie Nantuo glacial diamictites in south China are determined from the inner shelf to the slope. In general, shale-normalized REY patterns (REYSN) of the cap dolostones show significant fractionations that are characterized by light REE depletion, slight middle REE enrichment relative to the light and heavy REEs, positive Eu anomalies, and slightly super-chondritic Y/Ho ratios. [...]".

Source: Science Direct
Authors: Min Ren & Ruifan Li
DOI: https://doi.org/10.1016/j.sedgeo.2023.106343

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Abstract. 

"Early animals experienced multiple-phase radiations and extinctions from the late Ediacaran to early Cambrian. Oxygen likely played an important role in these evolutionary events, but detailed marine redox evolution during this period remains highly debated. The emerging vanadium (V) isotope system can better capture short-term perturbations to global ocean redox conditions. In this study, we analyzed V isotope compositions [...]".

Source: Science Direct 
Authors: Wei Wei et al.
DOI: https://doi.org/10.1016/j.epsl.2022.117942

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