Recent observations and modelling have shown that ocean warming and stagnation, driven by global climate change, may lead to widespread ocean deoxgyenation with direct impacts on marine biogeochemistry and ecosystems

Coe, A.

Cohen, A.

Izon, G.

Poulton, S.

Wagner, T.

English

Izon, G. J.

Cohen, A. S.

Coe, A. L.

Poulton, S. W.

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsMo-isotopes as tracers of Cretaceous ocean anoxiaConference or Workshop ItemHow to cite:Izon, G. J.; Cohen, A. S.; Coe, A. L.; Poulton, S. W. and Wagner, T. (2011). Mo-isotopes as tracers ofCretaceous ocean anoxia. In: Goldschmidt Conference 2011, 14-19 Aug 2011, Prague, Czech Republic.For guidance on citations see FAQs.c© 2011 Not knownVersion: Publication ExtractLink(s) to article on publisher’s website:https://goldschmidtabstracts.info/abstracts/abstractView?id=2011004283Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukGoldschmidt Conference Abstracts Mineralogical Magazine  www.minersoc.org 1091 !13C evidence of conodont evolution as a response to bioproduction perturbations O.P. IZOKH  Sobolev Institute of Geology, and Mineralogy SB RAS, Novosibirsk, Russia (izokhop@gmail.com)  Usually (13C variations in marine sediments are related to the mass extinction in the Earth’s past, and explained as reflection of the changes in primary bioproduction of the paleooceans, but sometimes the (13C excursion coincide with important evolutionary changes in biosphere. One of examples is radiation of polygnathid conodonts at the lower Emsian (Devonian), where negative (13, excursion (from +2 to -0.7 ‰) is aligned with the appearance of well-developed Pa element of the Polygnathus kitabicus, Pol. pannonicus and Pol. sokolovi. Apart of bioproduction decrease, carbonates secondary changes also may cause negative excursion. To exclude the diagenetic nature of these isotopic signals, investigations of geochemical criteria of primary carbonate material safety (Fe/Sr and Mn/Sr) have been done. Together with the petrographic studies they are very effective for allocation of diagenetically altered samples. All studied lower Emsian samples from Zinzilban section (Zeravshan Ridge, Kitab State Geological Reserve, Uzbekistan) are characterized by the low concentration of Fe (<100 ppm) and Mn (<22 ppm) with Sr contents from 150 to 400 ppm. Thus, Fe/Sr and Mn/Sr not exceed 0.5 and 0.07 accordingly, that evidence absence of carbonate material alteration. Also, it was controlled by petrographic studies. Thus, (13C negative excursion with high probability is a primary signal and the correlation of this event with the complication of conodont Pa element can reflect changes in their nutrition type, induced by the decreasing of the simple food. Mo-isotopes as tracers of Cretaceous ocean anoxia G.J. IZON1*, A.S. COHEN1, A.L. COE1, S.W. POULTON2 AND T. WAGNER 2 1Department of Earth and Environmental Sciences, The Open University, Milton Keynes, MK7 6AA, UK. (*correspondence: G.Izon@open.ac.uk) 2School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.  Recent observations and modelling have shown that ocean warming and stagnation, driven by global climate change, may lead to widespread ocean deoxgyenation with direct impacts on marine biogeochemistry and ecosystems. Measurements of marine oxygen levels extend back no more than c. 50 years, whilst accurate predictions of future deoxgyenation trends are difficult and uncertain. In contrast, the geological record of past abrupt global warming events can provide insights into the entire earth system response - the mechanisms, extent, duration and consequences of - seawater deoxgyenation that are associated with CO2-induced global warming.  The Cretaceous oceans were particularly susceptible to transient widespread deoxygenation, containing as many as 6 discrete intervals known as Ocean Anoxic Events (OAEs). Of these, OAE 1a (~120 Ma) and OAE 2 (~93 Ma) may have been global in extent and are marked by a sudden increase in organic C accumulation in conjunction with broad positive carbon isotope excursions.  We present new Mo-isotope, trace element and Fe-speciation analyses of samples from OAE 1a (the Selli event) and OAE 2 (the Bonarelli Event). Mo-isotope data can, under certain circumstances, provide quantitative estimates of how the extent of seawater anoxia may have fluctuated in the past. Our data from Gorgo a Cerbera, Italy, indicate that local conditions became progressively more reducing during OAE1a. (98/95Mo ratios show pronounced stratigraphic variations, consistent with diminished oxic sedimentation globally. Laminated sediments from Demerara Rise are enriched in redox sensitive trace metals (RSTM) throughout much of the Cenomanian. However, OAE 2 is marked by relatively low levels of RSTM consistent with the global expansion of anoxic sedimentation and the drawdown of the RSTM inventory. Our sample specific Fe-speciation data show that the water column was periodically euxinic, allowing us to use Mo-isotope data to critically test ideas on the timing, extent and duration of one of the most prounced  deoxgyenation events of the Mesozoic.      

Mo-isotopes as tracers of Cretaceous ocean anoxia

Mo-isotopes as tracers of Cretaceous ocean anoxia

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