scholarly journals The Plenus Cold Event Record in the Abyssal DSDP Site 367 (Cape Verde, Central Atlantic): Environmental Perturbations and Impacts on the Nitrogen Cycle

2021 ◽  
Vol 9 ◽  
Author(s):  
Laurent Riquier ◽  
Pierre Cadeau ◽  
Julien Danzelle ◽  
François Baudin ◽  
Emmanuelle Pucéat ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Water Column ◽  
Nitrogen Cycle ◽  
Cape Verde ◽  
Cold Event ◽  
Oceanic Anoxic Event ◽  
Carbon And Nitrogen ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Central Atlantic

The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of widespread burial of organic matter in marine sediments, underlined by a positive carbon-isotope (δ13C) excursion observed worldwide. Within this episode of O2-depleted conditions, a short interval of cooling, termed as the Plenus Cold Event, has been recorded in many sites and sections in the northern hemisphere (Tethyan domain, Western Interior Seaway, proto-North Atlantic Ocean). But, its record and its impact on the biogeochemical cycles of carbon and nitrogen in the southern part of Central Atlantic Ocean has not been explored yet. Here, we present a detailed geochemical study of the Deep Sea Drilling Project site 367 (Cape Verde) based on a compilation of previous and new data of carbon and nitrogen isotope signals as well as trace element concentrations. The aim of this study is to better constrain the evolution of oxygenation in the water column and the associated changes in nitrogen cycle before and during the Oceanic Anoxic Event 2 in order to understand the paleoceanographic and environmental consequences of the Plenus Cold Event at one of the deepest site of the Central Atlantic Ocean. Our new dataset improves the resolution of the δ13C curve for this site, and we propose a new chemo-stratigraphic frame of the carbon excursion allowing for a better identification of the short-term negative carbon isotope excursion associated to the Plenus Cold Event. The detailed evolution of redox-sensitive proxies (Mo, U, V, Fe, Cu, Ni enrichments and Corg/Ptotal) and isotopic signals (δ13Corg and δ15Ntotal) evidence that this deep site was impacted by this cooling event. While anoxic conditions prevailed in bottom waters before and during the onset of the Oceanic Anoxic Event 2 characterized by euxinic NH4+-rich water column, this cooling event was accompanied by reoxygenation of the water column, which had affected the behavior of the redox-sensitive elements and caused changes in nitrogen biogeochemical cycling.

The rhythmic expression of mid-Cretaceous Oceanic Anoxic Event 2 at IODP Sites U1513 and U1516 (southwest of Australia) 

2021 ◽  
Author(s):  
Sietske Batenburg ◽  
Kara Bogus ◽  
Matthew Jones ◽  
Kenneth Macleod ◽  
Mathieu Martinez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Indian Ocean ◽  
Water Column ◽  
North Atlantic ◽  
Black Shales ◽  
Carbonate Content ◽  
Intergovernmental Panel ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

<p>The widespread deposition of organic-rich black shales during the mid-Cretaceous hothouse at ~94 Ma marked a climatic extreme that is particularly well studied in the Northern Hemisphere. The expression of Oceanic Anoxic Event 2 (OAE 2) in the NH was characterised by low oceanic oxygen concentrations, likely caused by the input of nutrients through volcanism and/or weathering in combination with a peculiar geography in which the proto-North Atlantic was semi-restricted (Jenkyns, 2010; Trabucho Alexandre et al., 2010). The extent of water column anoxia outside the North Atlantic and Tethyan domains remains poorly resolved, as few Southern Hemisphere records have been recovered that span OAE 2, and only a portion of those Indian and Pacific Ocean localities experienced anoxia and organic matter deposition (Dickson et al., 2017; Hasegawa et al., 2013).</p><p> </p><p>Here we present new results from IODP Expedition 369 offshore southwestern Australia. Sedimentary records across the Cenomanian-Turonian transition from Sites U1513 and U1516 in the Mentelle Basin (Indian Ocean) display rhythmic lithologic banding patterns. The OAE 2 interval is marked by a dramatic drop in carbonate content and the occurrence of several thin organic-rich black bands. The spacing of dark bands within a rhythmic sequence suggests a potential orbital control on organic matter deposition at our study sites. Time series analyses of high-resolution (cm-scale) elemental data from XRF-core scanning reveal the imprint of periodicities that can be confidently linked to Earth’s orbital parameters. The new OAE 2 records from Sites U1516 and U1513 allow us to i) evaluate existing time scales over the Cenomanian-Turonian transition, and ii) investigate the mechanisms leading to a recurrent lack of oxygen in the Indian Ocean.</p><p> </p><p>Climatic mechanisms translating changes in insolation to variations in organic matter deposition may have included variations in nutrient input from nearby continents and shifts in water column structure affecting local to regional stratification versus deep water formation and advection. Investigating ventilation of the deep sea during the OAE2 interval is of heightened relevance as current global warming is leading to a worldwide expansion of oxygen minimum zones (Pörtner et al., 2019).</p><p> </p><p>References:</p><p>Dickson, A.J., et al., 2017. Sedimentology 64, 186–203.</p><p>Hasegawa, et al., 2013. Cretaceous Research 40, 61–80.</p><p>Jenkyns, H.C., 2010. Geochemistry, Geophysics, Geosystems 11, Q03004.</p><p>Pörtner, H.O., et al., 2019. IPCC Intergovernmental Panel on Climate Change: Geneva, Switzerland.</p><p>Trabucho Alexandre, J., et al., 2010. Paleoceanography 25, PA</p>

scholarly journals Equatorward phytoplankton migration during a cold spell within the Late Cretaceous supergreenhouse

2016 ◽  
Author(s):  
Niels A.G.M. van Helmond ◽  
Appy Sluijs ◽  
Nina M. Papadomanolaki ◽  
A.Guy Plint ◽  
Darren R. Gröcke ◽  
...  
Keyword(s):  
Bottom Water ◽  
Cold Spell ◽  
Cold Event ◽  
Climate Shift ◽  
Oceanic Anoxic Event ◽  
Rapid Climate Change ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

Abstract. Oceanic Anoxic Event 2 (OAE2), a ~600 kyr episode close to the Cenomanian-Turonian boundary (ca. 94 Ma), is characterized by widespread marine anoxia and ranks amongst the warmest intervals of the Phanerozoic. The early stages of OAE2 are, however, marked by an episode of widespread transient cooling and bottom water oxygenation: the Plenus Cold Event. This cold spell has been linked to a decline in atmospheric pCO2, resulting from enhanced global organic carbon burial. To investigate the response of phytoplankton to this marked and rapid climate shift we examined the biogeographical response of dinoflagellates to the Plenus Cold Event. Our study is based on a newly generated geochemical and palynological dataset from a high-latitude Northern Hemisphere site, Pratts Landing (western Alberta, Canada). We combine this data with a semi-quantitative global compilation of the stratigraphic distribution of dinoflagellate cyst taxa. The data show that dinoflagellate cysts grouped in the Cyclonephelium compactum-membraniphorum morphological plexus migrated from high- to mid-latitudes during the Plenus Cold Event, making it the sole widely found (micro)fossil to mark this cold spell. In addition to earlier reports from regional metazoan migrations during the Plenus Cold Event, our findings illustrate the effect of rapid climate change on the global biogeographical dispersion of phytoplankton.

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 Equatorward phytoplankton migration during a cold spell within the Late Cretaceous super-greenhouse

2016 ◽  
Vol 13 (9) ◽  
pp. 2859-2872 ◽  
Author(s):  
Niels A. G. M. van Helmond ◽  
Appy Sluijs ◽  
Nina M. Papadomanolaki ◽  
A. Guy Plint ◽  
Darren R. Gröcke ◽  
...  
Keyword(s):  
Bottom Water ◽  
Cold Spell ◽  
Cold Event ◽  
Data Set ◽  
Climate Shift ◽  
Oceanic Anoxic Event ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

Abstract. Oceanic Anoxic Event 2 (OAE2), a  ∼  600 kyr episode close to the Cenomanian–Turonian boundary (ca. 94 Ma), is characterized by relatively widespread marine anoxia and ranks amongst the warmest intervals of the Phanerozoic. The early stages of OAE2 are, however, marked by an episode of widespread transient cooling and bottom water oxygenation: the Plenus Cold Event. This cold spell has been linked to a decline in atmospheric pCO2, resulting from enhanced global organic carbon burial. To investigate the response of phytoplankton to this marked and rapid climate shift we examined the biogeographical response of dinoflagellates to the Plenus Cold Event. Our study is based on a newly generated geochemical and palynological data set from a high-latitude Northern Hemisphere site, Pratts Landing (western Alberta, Canada). We combine these data with a semi-quantitative global compilation of the stratigraphic distribution of dinoflagellate cyst taxa. The data show that dinoflagellate cysts grouped in the Cyclonephelium compactum–membraniphorum morphological plexus migrated from high to mid-latitudes during the Plenus Cold Event, making it the sole widely found (micro)fossil to mark this cold spell. In addition to earlier reports from regional metazoan migrations during the Plenus Cold Event, our findings illustrate the effect of rapid climate change on the global biogeographical dispersion of phytoplankton.

The Cenomanian–Turonian Oceanic Anoxic Event 2 and the Late Turonian-Coniacian Event in the Mexican Interior Basin

2021 ◽  
Author(s):  
Fernando Nunez ◽  
Azucena Colin-Rodríguez ◽  
Thierry Adatte ◽  
Lourdes Omaña-Pulido ◽  
Pura Alfonso ◽  
...  
Keyword(s):  
Cold Climate ◽  
Geochemical Data ◽  
Equatorial Atlantic ◽  
Cold Event ◽  
Climate Conditions ◽  
Oceanic Anoxic Event ◽  
Initial Stage ◽  
Igneous Provinces ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

<p>In the modern ocean, deoxygenation is a major consequence of climate change induced by eutrophication and expansion of oxygen minimum zones.  To better understand the exact mechanisms that promote the development of anoxia requires observations not available at human time scale, and therefore demand the study of intervals of rapid warming in the geologic past. During the Cretaceous Period, massive submarine volcanism during the construction of Large Igneous Provinces gave rise to the development of several episodes of widespread oxygen-depleted waters and enhance organic carbon deposition, including the  Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2) and the  Late Turonian–Coniacian Event (LTCE). In this study, we reconstruct climate and oceanographic conditions in the Mexican Interior Basin during these events, a key area that connected the Western Interior Seaway to the equatorial Atlantic Tethyan water mass. To accomplish this, we applied an integrated multi-proxy approach that includes sedimentological, microfacies, mineralogical and geochemical data from a upper Cenomanian–lower Coniacian section.</p><p>Organic-rich sediments were accumulated during the initial stage of OAE 2 and the middle stage of LTCE (Hitchwood Event), under increasingly warm and humid conditions, as evidenced by high chemical index of alteration (CIA) values. High detrital index (DI) values coupled with high phosphorus mass-accumulation rates suggest that this scenario increased detrital and nutrients fluxes. Eutrophic-anoxic/dysoxic marine conditions are corroborated by the highest TOC values coinciding with significant enrichments in redox- and productivity-sensitive trace elements. Moreover, they are supported by the abundant presence of radiolarians and filaments in the OAE 2 interval, and the occurrence of opportunistic foraminifera in the LTCE interval. Oxygen-depleted bottom waters are also indicated by Mo–U systematics and a small-sized population of pyrite. The onset of the Mexican Orogen tectonic uplift together with upwelling intensified the transference of nutrients and enhanced organic matter burial during the initial stage of OAE 2. In the mid-OAE 2 δ<sup>13</sup>C trough interval equivalent to the Plenus Cold Event, bioturbated sediments with low TOC values accumulated during a short episode of cold climate conditions reflecting the southward flow of boreal water throughout the Mexican Interior Basin. The minimum δ<sup>34</sup>S<sub>py</sub> value occurring within the OAE 2 interval in the Mexican Interior Basin is lower than elsewhere due to a local increase in sulfate concentrations.</p>

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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