scholarly journals Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2

2013 ◽  
Vol 6 (8) ◽  
pp. 668-672 ◽  
Author(s):  
Philip A. E. Pogge von Strandmann ◽  
Hugh C. Jenkyns ◽  
Richard G. Woodfine
Keyword(s):  
Lithium Isotope ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Isotope Evidence

Zinc isotope evidence for paleoenvironmental changes during Cretaceous Oceanic Anoxic Event 2

Geology ◽  
2020 ◽  
Author(s):  
Xi Chen ◽  
Bradley B. Sageman ◽  
Hanwei Yao ◽  
Sheng’Ao Liu ◽  
Kaibo Han ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Cold Event ◽  
Elevated Atmospheric Co2 ◽  
Oceanic Anoxic Event ◽  
Zinc Isotope ◽  
Igneous Provinces ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Isotope Evidence ◽  
Atmospheric Co2 Concentrations

Paleoclimate during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, 94.5–93.9 Ma) was characterized by elevated atmospheric CO2 concentrations and peak global temperatures. In this study, we employ δ66Zn measured on samples spanning OAE 2 in an expanded hemipelagic section in Tibet to trace changes in the major fluxes that influence biogeochemical cycles. The prominent feature of the δ66Zn record in the studied section is a continuous decrease from ~1‰ at the onset of OAE 2 to a minimum of ~0.2‰ within the Plenus Cold Event (ca. 94.3 Ma), followed by a stepwise recovery through the upper part of OAE 2. The negative shift in δ66Zn corresponds with higher terrigenous inputs, as revealed by previously published detrital index and TOC/TN (total organic carbon to total nitrogen) ratio records, and covaries with a notable decreasing trend recorded in compiled pCO2 data of different basins. We propose that influx of isotopically light Zn from weathered volcanic rocks associated with submarine large igneous provinces and/or (sub)tropic Indian continental volcanics is likely responsible for the δ66Zn decrease. We infer that the recovery of δ66Zn was caused by continued high primary production and an inevitable decline in the flux of light Zn as volcanic terrains were progressively weathered. The ultimate cessation of OAE 2 may have been a consequence of the same effect, with the nutrient supply from weathering reaching a minimum threshold to maintain productivity-anoxia feedback.

scholarly journals Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2

2018 ◽  
Vol 115 (12) ◽  
pp. 2918-2923 ◽  
Author(s):  
Matthew O. Clarkson ◽  
Claudine H. Stirling ◽  
Hugh C. Jenkyns ◽  
Alexander J. Dickson ◽  
Don Porcelli ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Large Igneous Province ◽  
Global Ocean ◽  
Uranium Isotopes ◽  
Carbonate Sediments ◽  
Cold Event ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Isotope Evidence

Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO2, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. We present a record of global ocean redox changes during OAE 2 using a combined geochemical and carbon cycle modeling approach. We utilize a continuous, high-resolution record of uranium isotopes in pelagic and platform carbonate sediments to quantify the global extent of seafloor anoxia during OAE 2. This dataset is then compared with a dynamic model of the coupled global carbon, phosphorus, and uranium cycles to test hypotheses for OAE 2 initiation. This unique approach highlights an intra-OAE complexity that has previously been underconstrained, characterized by two expansions of anoxia separated by an episode of globally significant reoxygenation coincident with the “Plenus Cold Event.” Each anoxic expansion event was likely driven by rapid atmospheric CO2injections from multiphase Large Igneous Province activity.

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