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Geochemical evidence from the Kioto Carbonate Platform (Tibet) reveals enhanced terrigenous input and deoxygenation during the early Toarcian

Abstract.

"The early Toarcian, as registered in a variety of sedimentary archives, was characterized by an abrupt negative carbon-isotope excursion (CIE) typically superimposed on a long-term positive trend, and was accompanied by significant climatic and environmental changes. However, the changes in continental weathering influx and oceanic deoxygenation in shallow waters and their possible role in causing carbonate-platform crises in low latitudes remains poorly constrained. [...]".

 

Source: Science Direct 
Authors: Zhong Han et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103887

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Decoupled oxygenation of the Ediacaran ocean and atmosphere during the rise of early animals

Abstract. 

"The Ediacaran Period (∼635 to 541 Ma) witnessed the early diversification and radiation of metazoans, in the form of the Ediacaran Biota. This biological revolution, beginning at ∼575 Ma, has been widely attributed to a temporally restricted episode of deeper ocean oxygenation, potentially caused by a contemporaneous rise in atmospheric oxygen levels. However, quantitative geochemical-record-driven estimates of Ediacaran atmospheric and oceanic redox evolution are lacking, and hence possible links between oceanic and atmospheric oxygenation remain speculative. [...]". 

 

Source: Science Direct 
Authors: Wei Shi et al.
DOI: https://doi.org/10.1016/j.epsl.2022.117619

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Enhanced phosphorus recycling during past oceanic anoxia amplified by low rates of apatite authigenesis

Abstract.

"Enhanced recycling of phosphorus as ocean deoxygenation expanded under past greenhouse climates contributed to widespread organic carbon burial and drawdown of atmospheric CO2. Redox-dependent phosphorus recycling was more efficient in such ancient anoxic marine environments, compared to modern anoxic settings, for reasons that remain unclear. Here, we show that low rates of apatite authigenesis in organic-rich sediments can explain the amplified phosphorus recycling in ancient settings as reflected in highly elevated ratios of organic carbon to total phosphorus. [...]".

 

Source: Science Advances 
Authors: Nina M. Papadomanolaki et al.
DOI: 10.1126/sciadv.abn2370

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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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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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Marine anoxia linked to abrupt global warming during Earth’s penultimate icehouse

Abstract.

"Piecing together the history of carbon (C) perturbation events throughout Earth’s history has provided key insights into how the Earth system responds to abrupt warming. Previous studies, however, focused on short-term warming events that were superimposed on longer-term greenhouse climate states. Here, we present an integrated proxy (C and uranium [U] isotopes and paleo CO2) and multicomponent modeling approach to investigate an abrupt C perturbation and global warming event (∼304 Ma) that occurred during a paleo-glacial state. We report pronounced negative C and U isotopic excursions coincident with a doubling of atmospheric CO2 partial pressure and a biodiversity nadir. [...]".

 

Source: Proceedings of the National Academy of Sciences
Authors: Jitao Chen et al.
DOI: https://doi.org/10.1073/pnas.2115231119

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