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Testing the links between mass extinctions, volcanism and ocean chemistry


   Faculty of Environment

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  Assoc Prof Robert Newton, Dr Benjamin Mills, Prof Paul Wignall, Dr T Aze  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Why do some large volcanic eruptions create mass extinctions whilst others don’t? There is an emerging link between volcanically driven mass extinctions, such as those at the Permo-Triassic boundary and the end-Triassic, the development of anoxia, and low concentrations of sulfate in the oceans (He et al, 2020). Is this link coincidental or could it partly explain why not all large volcanic eruptions cause severe extinction?

Ocean sediments are key components of marine biogeochemical cycles and host a suite of important reactions driven by organic matter and facilitated by bacteria. Sulfate-reducing bacteria oxidise organic carbon to CO2 after oxygen has run out, whilst deeper in the sediment, methanogenic bacteria produce methane from the organic carbon that remains. Unchecked, this methane could diffuse upwards to the water column and consume dissolved oxygen, however, sulfate can also be used by third group of bacteria to oxidise methane, thus preventing it from reaching the water column. In the modern ocean sulfate is very abundant and the combined effect of these microbial communities is to limit both methane production (by consuming organic carbon), and release (by consuming methane itself), largely preventing any impact on dissolved oxygen. When sulfate is lower however, a much greater proportion of the organic carbon is transformed to methane, and much more of this methane is able to escape into the water column where it’s oxidised using oxygen. This oxygen consumption can then speed up the transition to anoxic conditions which are linked to extinction. This additional oxygen demand in low sulfate oceans may form a new and powerful mechanism that makes a low-sulfate ocean predisposed to widespread anoxia and marine extinction during volcanically driven warming events.

This project will focus on records and models of the sulfur cycle and its links to other biogeochemical cycles during volcanically driven warming events to answer the following questions:

1)   How did ocean sulfate concentrations vary before, during and after the events?

2)   How might the sulfur and carbon cycles interact to control the dissolved oxygen concentrations of the oceans during these events?

These questions will be applied to two case studies: One from an event with a proven anoxia-mass extinction link (likely to be the Permo-Triassic event); and one from a volcanic event of a similar magnitude where evidence for anoxia and its biological impact is far more limited (such as one of the Cretaceous oceanic anoxic events or the Palaeocene-Eocene thermal maximum).

The student will work on two novel techniques to infer past ocean sulfate concentrations. These are based on the substitution of sulfate into phosphate (McArthur, 1985; Piper and Kolodny, 1987) and carbonate minerals in tiny organisms called foraminifera (Paris et al., 2014). Both phosphate deposits and foraminifera have a much more continuous record than more traditional sulfate deposits (evaporites) and can be dated with far greater precision, creating the potential for capturing fluctuations in ocean sulfate that occur on short timescales. These methods can then be applied to the selected events to determine marine sulfate levels, and the data can be used to develop a simple biogeochemical computer model to test how the ocean in this state might respond to a warming event. The modelling will build on current frameworks developed by the supervisory team (e.g. Mills et al., 2016; 2019) to add in the links to the methane cycle and its effect on marine oxygen levels.

For full project description see here:

https://panorama-dtp.ac.uk/research/testing-the-links-between-mass-extinctions-volcanism-and-ocean-chemistry/


Funding Notes

This project is advertised as part of the Panorama NERC Doctoral Training Program but could also be offered for self or external funding.

References

He, T., Dal Corso, J., Newton, R. J., Wignall, P. B., Mills, B. J. W., Todaro, S., Di Stefano, P., Turner, E. C., Jamieson, R. A., Randazzo, V., Rigo, M., Jones, R. E., and Dunhill, A. M., 2020, An enormous sulfur isotope excursion indicates marine anoxia during the end-Triassic mass extinction: Science Advances, v. 6, no. 37, p. eabb6704.
Hall, J.L.O., Newton, R.J., Witts, J.D., Francis, J.E., Hunter, S.J., Jamieson, R.A., Harper, E.M., Crame, J.A., and Haywood, A.M., 2018, High benthic methane flux in low sulfate oceans: Evidence from carbon isotopes in Late Cretaceous Antarctic bivalves. Earth and Planetary Science Letters, 497: 113-122.
Horita, J., Zimmermann, H., Holland, H.D., 2002. Chemical evolution of seawater during the Phanerozoic: Implications from the record of marine evaporites. Geochimica et Cosmochimica Acta, 66(21): 3733-3756.
McArthur, J.M., 1985. Francolite geochemistry--compositional controls during formation, diagenesis, metamorphism and weathering. Geochimica et Cosmochimica Acta, 49(1): 23-35.
Mills, B.J.W., Belcher, C.M., Lenton, T.M. & Newton, R.J. 2016. A modeling case for high atmospheric oxygen concentrations during the Mesozoic and Cenozoic. Geology 44, 1023-1026.
Mills, B.J.W., Krause, A.J., Scotese, C.R., Hill, D.J., Shields, G.A.and Lenton, T.M. et al. Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day. 2019. Gondwana Research 67, 172-186.
Paris, G., Fehrenbacher, J.S., Sessions, A.L., Spero, H.J., Adkins, J.F., 2014. Experimental determination of carbonate-associated sulfate δ34S in planktonic foraminifera shells. Geochemistry, Geophysics, Geosystems, 15(4): 1452-1461.
Piper, D.Z., Kolodny, Y., 1987. The stable isotopic composition of a phosphorite deposit: d13C, d34S, and d18O. Deep Sea Research Part A. Oceanographic Research Papers, 34(5-6): 897-911.
Witts, J.D., Newton, R.J. Mills B.J.W., Wignall, P.B., Bottrell, S.H., Hall, J.L.O., Francis, J.E. and Crame, J.A., 2018. "The impact of the Cretaceous–Paleogene (K–Pg) mass extinction event on the global sulfur cycle: Evidence from Seymour Island, Antarctica." Geochimica et Cosmochimica Acta 230: 17-45.

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