Lead supervisor: David Munday, British Antarctic Survey
Co-supervisor: Kate Hendry, British Antarctic Survey; Ali Mashayek, Earth Sciences; Alex Piotrowski, Earth Sciences
Brief summary:
The Eocene, 55 to 34 million years ago, was a time of great climatic change with global temperature and atmospheric carbon dioxide both reducing. Ocean circulation was greatly altered by the tectonic rearrangement of the continents. This project will investigate the role of vertical mixing in the ocean over this time frame and how it affected ocean carbon storage.
Importance of the area of research concerned:
Climate change is driven by anthropogenic emissions of carbon dioxide. This has led to an unprecedented increase in atmospheric carbon dioxide and elevated global temperatures. Understanding future climate trends is crucial to predicting how human society and life will be impacted. One route to increase this understanding is to consider past climate, which may provide useful comparators. A possible comparator is the Eocene, which was a time of warm, equable climate with elevated atmospheric carbon dioxide. The gradual decline of atmospheric carbon dioxide and global temperature towards pre-industrial levels over millions of years was accompanied by large changes in ocean circulation, in part due to the opening and closing of ocean gateways as the continents were tectonically rearranged. A deep understanding of how these different elements fit together will improve our understanding of the Earth system as a whole. This will improve our ability to predict future climate and our chance to mitigate its greatest impacts.
Project summary :
A relatively unexplored aspect of Eocene climate change is how vertical ocean mixing may impact the evolution of Eocene ocean circulation and where the Eocene ocean stored carbon. As ocean gateways evolved, particularly in the Southern Ocean and the closing of the Panama Isthmus, vertical mixing would also have been rearranged. This would lead to changes in where the ocean stored carbon. This project will use an idealised two basin numerical ocean model to represent the Pacific and Atlantic. This model uses simple surface forcing to drive plausible Eocene and modern circulations. This flexible framework will allow the student to alter the strength and location of vertical mixing and compare the simulated circulations. Aspects of interest, such as gateway width or depth, can be quickly altered opening up a wide range of scenarios for investigation.
What will the student do?:
The student will design perturbation experiments for the idealised model to test ideas and theories on how ocean circulation may have changed. They will begin by considering vertical mixing processes and how this changes Eocene circulation. A biogeochemical model, coupled to the ocean circulation, will quantify how and why atmospheric carbon dioxide levels are affected. The perturbation experiments will concentrate on how changes in ocean circulation alter the distribution of biogeochemical tracers, particularly dissolved carbon. This will lead to changes in atmospheric carbon dioxide and is thus a route to climate change.
The student will be expected to steer the direction of the project in its later stages, giving them the opportunity to establish their scientific independence and formulate their own research plans. This will allow them to choose the direction of their research to follow promising leads and their own interests. For example, the idealised model framework is very flexible, allowing the student to introduce other aspects of the Eocene-modern climate transition such as changing ocean gateway depths or basin width/extent.
References - references should provide further reading about the project:
D. R. Munday, L. C. Allison, H. L. Johnson, and D. P. Marshall, 2011. Remote forcing of the Antarctic Circumpolar Current by diapycnal mixing, Geophys. Res. Lett., 38, L08609, doi:10.1029/2011GL046849.
I. Sauermilch, J. M. Whittaker, A. Klocker, D. R. Munday, K. Hochmuth, J. H. LaCasce, and P. K. Bijl, 2021. Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling, Nat. Commun., 12, 6465, doi:10.1038/s41467–021–26658–1.
Y. Zhang, A. M. de Boer, D. J. Lunt, D. K. Hutchinson, P. Ross, T. van de Flierdt, P. Sexton, H. K. Coxall, S. Steinig, J. -B. Ladant, J. Zhu, Y. Donnadieu, Z. Zhang, W. -L. Chan, A. Abe-Ouchi, I. Niezgodzki, G. Lohmann, G. Knorr, C. J. Poulsen, and M. Huber, 2022. Early Eocene ocean meridional overturning circulation: The roles of atmospheric forcing and strait geometry. Paleoceanogr. Paleoclimatol., 37, e2021PA004329, doi:10.1029/2021PA004329.
Applying
You can find out about applying for this project on the British Antarctic Survey (BAS) page.