The Ocean Giant of the Warm World: Pliocene Changes in Pacific Palaeogeographyeardjh@leeds.ac.uk
The impacts of the Pacific Ocean on contemporary climate change and natural warming since the last Ice Age are increasingly being recognised (Kosaka and Xie, 2013; Skinner et al., 2015). However, its state and role in the warmer-than-modern climates of the recent geological past are still debated (Rickaby and Halloran, 2005; Wara et al., 2005; Li et al., 2011; Zhang et al., 2014). The Pliocene is the last period of Earth history with elevated surface temperatures and atmospheric carbon dioxide concentrations close to today (Pagani et al., 2010; Haywood et al., 2013). The North Atlantic has long been investigated for its role in the warm climate of the Pliocene (Dowsett et al., 1992; Raymo et al., 1996), but evidence that the Pacific Ocean also played a key role has emerged in recent years (Federov et al., 2013; Nie et al., 2014). There are, however, many uncertainties in the palaeogeography of the surrounding continents, ocean gateways and shallow seas (Figure 1). These have yet to be systematically incorporated into models of the Pliocene climate and may significantly impact the state of the Pacific Ocean.
Figure 1: Circum-Pacific palaeogeographic changes in the Pliocene. (A) Indonesian archipelago and throughflow currents (Karas et al., 2009), (B) Antarctic ice sheets (Haywood et al., 2010), (C) topography in the Rockies and Andes mountain chains (Haywood et al., 2010), (D) Central American Seaway prior to the final uplift of the Isthmus of Panama (Coates et al., 2014), (E) a closed Bering Strait during the Pliocene (Haywood et al., 2016) and (F) and the Japanese archipelago (Kamado and Kato, 2011).
The discrepancy between proxy sea surface temperature reconstructions in the Pliocene Pacific Ocean have been used to suggest that climate models are unable to reproduce the behaviour of the Pacific Ocean under warm climates of the past. Various mechanisms and possible changes in the Earth system have been suggested as a solution to this discrepancy, including altered ENSO dynamics (Rickaby and Halloran, 2005; Wara et al., 2005), enhanced ocean mixing (Federov et al., 2010) and altered cloud albedo impacts (Burls and Federov, 2014). If one or more of these mechanisms is indeed important for correctly simulating warmer than modern climates, then they could also be an important mechanism for simulating future climate warming. However, there has never been a comprehensive analysis of the potential impacts of palaeogeographic changes in the region to test whether models would reproduce the reconstructed temperatures given other plausible Pliocene boundary conditions, without having to invoke changes in the observed operation of climate.
This project will build an ensemble of General Circulation Model (GCM) simulations, using the Hadley Centre climate model, incorporating the circum-Pacific palaeogeographic changes. These will be used to investigate the state of the Pliocene Pacific Ocean and its sensitivity to the nature of these changes. Many different aspects of the Pacific Ocean will be investigated, including the oceanic temperatures and circulation, the internal variability of the El Niño Southern Oscillation (ENSO) and the impact of Pacific temperatures on the neighbouring monsoonal systems (Asian, Australian, South American and African). The project will also draw on the international Pliocene climate modelling project, with the PhD candidate able to lead on the Pacific Meridional Ocean Circulation analysis within PlioMIP (Pliocene Model Intercomparison Project).
The student will undertake a systematic modelling study of the Pliocene Pacific Ocean, in collaboration with their supervisors, the Palaeo@Leeds research group and palaeoclimate modellers from across the globe. There is plenty of scope for the student to tailor the project and prioritise the various aspects of the project according to their own interests. However, the following would be a reasonable expectation for the project.
- Produce an ensemble of Pliocene climate model simulations, incorporating circum-Pacific palaeogeographic changes. These will include changes in the Indonesian Archipelago, Japan Sea, Bering Strait, Rockies, Andes and Antarctica.
- Analyse the results of the ensemble in terms of the mean state of the Pacific and the climate variability in the region. Records of ocean temperature, circulation, ENSO and monsoons will test the impact of Pliocene palaeogeographic change in the Pacific region on global climate. This will also provide a test of whether the observed changes in the Pliocene Pacific are within the bounds of palaeogeographic uncertainties or require changes in the operation of climate in warmer than modern palaeoclimates.
- Investigate the Pacific Ocean climate in PlioMIP phase 2 ensemble, testing the model dependency of Pliocene climate simulations. The student will lead the analysis of the Pacific Ocean circulation in PlioMIP phase 2.
Potential for high impact outcome
The Pliocene Pacific Ocean has been a hot topic in palaeoclimatology and palaeoceanography for a number of years (Rickaby and Halloran, 2005; Wara et al., 2005) and continues to produce high impact papers (Zhang et al., 2014). New International Ocean Discovery Programme (IODP) cores from the Western Pacific Warm Pool will keep this topic high on the scientific agenda (Rosenthal et al., 2016). Not only will the project produce a unique and important modelling ensemble, which will have important implications for new proxy reconstructions, but it will be able to draw on PlioMIP Phase 2, enabling the student to lead an aspect of the analysis of at least 14 climate models from around the world (Haywood et al., 2016).
With the supervisors’ long history of simulating the Pliocene climate using these models, it is anticipated that the student will get up to speed quickly and will soon be presenting relevant results at international conferences and in publications. The publication strategy would depend on the results that are produced, but at least 2 high impact publications (palaeogeographic changes and PlioMIP results) would be anticipated from the project.
The successful candidate will work closely with supervisors, Daniel Hill and Alan Haywood, and will play an active role in Palaeo@Leeds research group. Interacting with this group will give the student a broad education in cutting edge palaeoclimate and palaeontological research. Specific training in the use of climate models and high performance computing will be given both in Leeds and at external training courses. Being part of the Leeds/York NERC DTP (Natural Environment Research Council Doctoral Training Programme) will also give the student access to lots of training in general research and academic skills. Being part of the PlioMIP project will give the student experience of working will lots of different climate models and handling large data sets. The student will also be expected to interact with lots of different scientists and disciplines that work on the Pacific Ocean and the Pliocene Epoch. This will be facilitated by attendance and presentation at a series of major international conferences. The Urbino summer school in Italy provides general training in palaeoclimate research and the student would be expected to apply to attend the course in summer 2018.
Palaeoclimate modelling is by necessity a multi-disciplinary research area and no candidate will have existing skills in all the necessary disciplines. Applications are particularly encouraged from candidates with a background in physical science, mathematics, Earth science or oceanography. However, as all training will be given to successful candidates, those with any quantitative scientific background would also be suitable.
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Nie, J., Stevenes, T., Song, Y., King, J.W., Zhang, R., Ji, S., Gong, L. and Cares, D., 2014. Pacific freshening drives Pliocene cooling and Asian monsoon intensification. Scientific Reports, 4, 5474.
Pagani, M., Liu, Z., LaRiviere, J. and Ravelo, A.C., 2010. High Earth-system sensitivity determined from Pliocene carbon dioxide concentrations. Nature Geoscience, 3, 27-30.
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Skinner, L., McCave, I.M., Carter, L., Fallon, S., Scrivner, A.E. and Primeau, F., 2015. Reduced ventilation and enhanced magnitude of the deep Pacific carbon pool during the last glacial period. Earth and Planetary Science Letters, 411, 45-52.
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Related undergraduate subjects:
- Earth science
- Physical science