Project highlights

  • Training in development and application of a climate model
  • Perform the first transient 3D coupled climate-ocean-carbon cycle simulations across orbital cycles during a greenhouse climate
  • Test theories for the sensitivity of deep ocean circulation to orbital cycles in insolation across different background climate states


The meridional overturning circulation (MOC) comprises planetary-scale oceanic flows that are of direct importance to Earth’s global climate system because they transport vast amounts of heat, salt and nutrients around the planet1. Ocean circulation also regulates the exchange of CO2 between the vast ocean interior carbon reservoir and the comparatively tiny atmospheric reservoir1 that is 60 times smaller. The MOC, and in particular, the Atlantic’s MOC, is now known to have responded very sensitively to changes in insolation imparted by modulations in Earth’s solar orbit across the Pleistocene ice age cycles and played a crucial role in driving Earth into, and out of, these ice ages1. The need to better understanding the MOC is underscored by the fact that computer models predict the Atlantic’s MOC could weaken, shoal, or even disappear, in response to ongoing global warming, with profound consequences for regional climate change.

Human-induced CO2 emissions are projected to elevate atmospheric concentrations of this greenhouse gas to levels that, by 2100, will be higher than at any time since the climatic ‘greenhouse’ of the Eocene epoch (56 to 33 million years ago)2,3. Yet there exist no geological data with which to determine whether a MOC even existed during the Eocene greenhouse or how any MOC may have differed from its modern counterpart. A major unanswered question that this PhD will tackle are to determine what processes govern deep water formation dynamics in an extreme greenhouse climate at the timescales of Earth’s orbital cycles. Another key question is what was the sensitivity of an Eocene MOC to, or role in driving, climatic change at the timescales of Earth’s orbital cycles3?

The successful candidate will explore what processes governed deep water formation dynamics in an Eocene greenhouse climate. They will also evaluate the response of Eocene ocean circulation to the changes in insolation imparted by cycles in Earth’s solar orbit, and determine whether the nature of this response differs from that known from colder climates. The broader goal of the project is to provide a comprehensive picture of the controls on deep ocean circulation across contrasting climate states.


The Open University


  • Climate and Environmental Sustainability


Project investigator



  • Philip Sexton
  • Neil Edwards
  • Dan Lunt (Bristol University)

How to apply


This project will apply PLASIM-GENIE, a recently developed intermediate complexity 3D dynamic atmosphere-ocean model with a coupled carbon cycle climate model that has been applied in future4 and in several paleoclimate studies, extending back to the Eocene. It is significantly more efficient than other models in its class, enabling application to new scientific problems that have hitherto been computationally intractable. The project will first involve setting up Eocene model configurations with different ocean gateways5 (e.g. open or closed Drake Passage, Arctic-North Atlantic gateways), and evaluate which configuration best fits the available data (from the literature, plus exciting new datasets recently produced in our OU labs). Simulation ensembles will be run that account for orbital variability and model uncertainties. Simulations will be supplemented by well-developed emulation approaches5 to calibrate the response, explore the drivers of variability and generate time-series of key Earth system metrics to aid comparisons of model output with palaeoceanographic data. The student will also establish the precise phasing between the palaeoceanographic datasets (documenting MOC changes) and orbital cycles3 for each epoch (Eocene, Pliocene and Pleistocene).

Training and skills

Full support will be provided to the student to learn how to install, configure and run complex climate models and analyse their outputs. There will be training in statistical skills, using state-of-the-art approaches in ensemble design and statistical emulation. To establish the phasing between palaeoceanographic data and orbital cycles for each epoch the student will be trained in using advanced time series analysis and signal processing software to calibrate the available datasets to the latest solutions of Earth’s orbital cycles.

Partners and collaboration

The supervisory team are leading members of the modelling community involved in model intercomparison projects to coordinate the ability of different models to simulate the large climate changes that occurred in the geological past. This will provide the successful candidate with an invaluable link to the established palaeoclimate modelling community and connections to the wider global Intergovernmental Panel on Climate Change (IPCC) climate modelling community. Project results will also help meet the ambitious scientific goals of IODP Exp. 342 (from which some of the palaeoceanographic datasets have been generated), and the successful candidate will have opportunities to interact and collaborate with IODP Exp. 342 scientists (

Further details

Applications should include:

  • an academic CV containing contact details of three academic references
  • a CENTA application form
  • and an Open University application form, downloadable from:



Applications should be sent to  by 11.01.2021 

Possible timeline

Year 1

Literature survey and extraction of published Eocene data and knowledge. Develop Eocene boundary conditions and submit simulation ensembles. Present simulations at a virtual conference.

Year 2

Apply statistical approaches to evaluate paleogeographies that best fit observational data and assess the Earth system parameters that drive variability in deep water formation for publication. Present results at an online conference such as Palaeo PERCS (; for early career researchers).

Year 3

Calibrate existing palaeoceanographic datasets to orbital solutions and integrate with the modelling results to explore orbital variability of deep water formation dynamics in an Eocene greenhouse climate for a second publication. Compare orbital controls on ocean circulation across contrasting climate states for a third publication. Present results at an international conference. Write thesis chapters for submission.

Further reading

  1. Adkins, J., 2013. The role of deep ocean circulation in setting glacial climates. Paleoceanography, 28, 539-561.
  2. Anagnostou, E., John, E.H., Babila, T.L., Sexton, P.F. et al., 2020. Proxy evidence for state-dependence of climate sensitivity in the Eocene greenhouse, Nature Communications, 11, 4436.
  3. Westerhold, T. et al., 2020. An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science, 369, 1383-1387.
  4. Holden, P.B., Edwards, N.R, et al., 2018. Climate-carbon cycles uncertainties and the Paris Agreement, Nature Climate Change, 8, 609-613.
  5. Thomson, J.R., Holden, P.B., Anand, P., Edwards, N.R., Porchier, C.A. Harris, N.W.B., in review. Tectonic and climatic drivers of Asian monsoon evolution, Nature Communications.


Covid-19 risks are minimal. The project is fully model-based, with experiments performed on the OU computing cluster, which can be readily accessed via VPN from any good internet connection. Supervisory meetings will be via Microsoft Teams while this remains necessary.