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Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system

Abstract. 

"We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. [...]".

 

Source: Science Direct 
Authors: Thomas Steuber et al.
DOI: https://doi.org/10.1016/j.palaeo.2022.111086

Read the full article here.


LIP volcanism (not anoxia) tracked by Cr isotopes during Ocean Anoxic Event 2 in the proto-North Atlantic region

Abstract.

"Chromium is a redox sensitive element that exhibits a large range of isotopic compositions in Earth’s surface environments because of Cr(VI)-Cr(III) transformations. This property of Cr has been exploited as a tracer of Earth’s oxygenation history using marine sediments. However, paleoredox applications using Cr are difficult to implement due to its complicated cycling, which creates spatial variability in seawater δ53Cr values. Applications are further hindered by the potential for variability in the major inputs of Cr, such as submarine volcanism, to mask redox processes. [...]". 

 

Source: Science Direct 
Authors: Lucien Nana Yobo et al.
DOI: https://doi.org/10.1016/j.gca.2022.06.016

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Major sulfur cycle perturbations in the Panthalassic Ocean across the Pliensbachian-Toarcian boundary and the Toarcian Oceanic Anoxic Event

Abstract. 

"The early Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) was characterized by marine deoxygenation and the burial of organic-rich sediments at numerous localities worldwide. However, the extent of marine anoxia and its impact on the sulfur cycle during the T-OAE is currently poorly understood. Here, stable sulfur isotopes of reduced metal-bound sulfur (δ34Spyrite) and pyrite sulfur concentrations (SPY) have been analyzed across the Pliensbachian-Toarcian boundary (Pl-To) and the T-OAE from the Sakahogi and Sakuraguchi-dani sections (Japan), which were deposited in the deep and shallow Panthalassic Ocean, respectively. [...]".

 

Source: Science Direct 
Authors: Wenhan Chen et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103884

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The palynology of the Toarcian Oceanic Anoxic Event at Dormettingen, southwest Germany, with emphasis on changes in vegetational dynamics

Abstract.

"The Toarcian Oceanic Anoxic Event (T-OAE; ~ 183 Ma) represents an episode of marine anoxia that lasted for several hundred thousand years. Abiotic factorscontributing to the formation of the T-OAE, such as global warming, changes in weathering intensity, or sea-level change, are associated with a marked change in carbon cycling. While these factors are well studied, detailed palynological data, including marine and terrestrial palynomorphs, is still missing. Here we present comprehensive palynological data from the sedimentologically and geochemically well constrained T-OAE section in Dormettingen (SW Germany). [...]".

 

Source: Science Direct 
Authors: Francesca Galasso et al.
DOI: https://doi.org/10.1016/j.revpalbo.2022.104701

Read the full article here.


Intensive peatland wildfires during the Aptian–Albian oceanic anoxic event 1b: Evidence from borehole SK-2 in the Songliao Basin, NE China

Abstract. 

"The Cretaceous has been considered a “high-fire” world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. [...]".

 

Source: Science Direct 
Authors: Zhi-Hui Zhang et al.
DOI: https://doi.org/10.1016/j.jop.2022.06.002

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Isotopic evidence for changes in the mercury and zinc cycles during Oceanic Anoxic Event 2 in the northwestern Tethys, Austria

Abstract. 

"The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. Widespread deposition of organic-rich shales during OAE 2 has been attributed to a rapid rise in atmospheric CO2, global heating, and marine anoxia triggered by intense large igneous province (LIP) volcanism. Here, we present new Hg and Zn elemental and isotopic analyses from samples spanning OAE 2 in a hemipelagic section from Rehkogelgraben, Austria, which was part of the north-western Tethys. [...]".

 

Source: Science Direct 
Authors: Hanwei Yao et al.
DOI: https://doi.org/10.1016/j.gloplacha.2022.103881

Read the full article here.


Uranium isotope reconstruction of ocean deoxygenation during OAE 2 hampered by uncertainties in fractionation factors and local U-cycling

Abstract. 

"A δ238U record of changing ocean anoxia during OAE 2 is reconstructed using seawater derived U in pelagic marine sediments in the Portland #1 core in the south-central region of the Western Interior Seaway of North America. The peak negative excursion of 1.4‰ in authigenic sedimentary δ238U values is consistent with expansion of marine anoxia during the event, but the size of the shift is much larger than the negative excursions recorded in two other published records. [...]". 

 

Source: Science Direct 
Authors: Brayden S. McDonald et al.
DOI: https://doi.org/10.1016/j.gca.2022.05.010

Read the full article here.


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 

Read the full article here.


Mid-Cretaceous marine Os isotope evidence for heterogeneous cause of oceanic anoxic events

Abstract. 

"During the mid-Cretaceous, the Earth experienced several environmental perturbations, including an extremely warm climate and Oceanic Anoxic Events (OAEs). Submarine volcanic episodes associated with formation of large igneous provinces (LIPs) may have triggered these perturbations. The osmium isotopic ratio (187Os/188Os) is a suitable proxy for tracing hydrothermal activity associated with the LIPs formation, but 187Os/188Os data from the mid-Cretaceous are limited to short time intervals. Here we provide a continuous high-resolution marine 187Os/188Os record covering all mid-Cretaceous OAEs. Several OAEs (OAE1a, Wezel and Fallot events, and OAE2) correspond to unradiogenic 187Os/188Os shifts, suggesting that they were triggered by massive submarine volcanic episodes. However, minor OAEs (OAE1c and OAE1d), which do not show pronounced unradiogenic 187Os/188Os shifts, were likely caused by enhanced monsoonal activity. [...]".

 

Source: Nature Communications 

Authors: Hironao Matsumoto et al.

DOI: https://doi.org/10.1038/s41467-021-27817-0

Read the full article here.


Cretaceous oceanic anoxic events prolonged by phosphorus cycle feedbacks

Abstract.

"Oceanic anoxic events (OAEs) document major perturbations of the global carbon cycle with repercussions for the Earth's climate and ocean circulation that are relevant to understanding future climate trends. Here, we compare the onset and development of Cretaceous OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). OAE1a and OAE2 exhibit remarkable similarities in the evolution of their carbon isotope (δ13C) records, with long-lasting negative excursions preceding the onset of the main positive excursions, supporting the view that both OAEs were triggered by massive emissions of volcanic CO2 into the atmosphere. However, there are substantial differences, notably in the durations of individual phases within the δ13C positive excursions of both OAEs. [...]"

Source: Climate of the Past
Authors: Sebastian Beil et al.
DOI: 10.5194/cp-16-757-2020

Read the full article here.


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