A climate model for Pleistocene glacial cycles
Supervisory Team ● Prof. Ian Hewitt – https://people.maths.ox.ac.uk/hewitt/ ● Prof. Richard Katz – https://www.earth.ox.ac.uk/people/richard-katz/ ● Prof. Peter Huybers – collaborator, Harvard
Key Words Glacial cycles, climate, ice sheet, modelling
This project is suitable for applicants with a training in applied mathematics, physics, theoretical and applied mechanics, engineering and geophysical fluid dynamics. The student could become part of either the Earth Science or Mathematics departments.
Methodology Overview The project is theoretical and computational in Glacial cycles of the last 2 million years respond to nature, requiring the student to gain a broad variations in insolation forcing, and in particular to understanding of climate physics and the Northern hemisphere summer insolation. These mathematics used to simulate long term changes insolation variations are a consequence of the in climate. This includes radiative balance, Milankovitch cycles – eccentricity, obliquity and ice-sheet dynamics (including isostasy and precession – that have periodicities of ~100ka, hydrology), and the carbon cycle(s). 41ka and ~23ka, respectively. The student will analyse an existing model that This DPhil project will develop low-complexity couples atmospheric temperature and carbon with climate models to test hypotheses regarding a simple ice-sheet. The model will then be climate dynamics and its sensitivity to orbital modified to incorporate pro-glacial lakes, ice variations. The aim is to better understand the calving, and a more detailed model of isostasy. characteristics of Pleistocene glacial cycles. The basal boundary conditions of the ice will be reconsidered to account for basal melting and While terrestrial insolation forcing can be hydrology-dependent ice sliding. These changes reconstructed with high accuracy from orbital will introduce new time-scales and non-linearities models, the climate response is not well into the problem. It will be a key aim of the project understood. For example, glacial cycles had a to understand the consequences of each for the dominant period of ~41ka in the early Pleistocene, detailed response of the climate model to orbital but in the late Pleistocene, they took on much forcing. Further feedbacks may be incorporated more power in the ~100ka and ~20ka bands. The and studied as the project progresses and throws cause of this shift is debated. Furthermore, the up new questions. sea-level curve over this period indicates that ice sheets build slowly and decay rapidly. The models will be expressed as a combination of ordinary and partial differential equations. These Although a wide range of models have been used will be solved numerically and the student will learn to examine glacial variability, few are positioned to to develop and test the necessary code, building represent interactions amongst ice, atmosphere, on existing examples. Some aspects of the model ocean, and land and afford for simulation over may be susceptible to model reduction, where multiple glacial cycles. This project will build on certain processes can be simplified or and critically re-assess past work to develop a approximated analytically; such reductions will be model capable of testing various orbital explored in order to reduce the run-times. hypotheses for the glacial cycles.The ice-sheet model, in particular, will be updated to include a Model outputs will be compared to paleo records modern understanding of basal temperature such as temperature proxies and atmospheric CO 2 regimes, ice sliding, and rapid ice-sheet concentration from ice cores, and reconstructions instabilities associated with calving. of past sea level. Timeline The timeline will depend on the specific interests and role of the student within the project. The following is an example.
Year 1: DTP training courses, literature review, development of research plan.
Years 2 and 3: code development, systematic testing and investigation, comparison with simpler models and available data.
Year 4: Data integration, thesis completion, papers for international journals/conference presentation.
Training & Skills The Oxford Doctoral Training Programme offers courses in mathematical and computational methods for geoscientific research, plus a variety of short courses to increase the breadth of your knowledge. These would occupy a part of the first year.
The supervisory team in Oxford would then provide guidance and teaching in the physics and mathematics of the problem. Collaboration with Huybers will ensure a broader perspective on palaeoclimate: comparison with observations, model benchmarking and validation,
References & Further Reading
Weertman, J. (1976). Milankovitch solar radiation variations and ice age ice sheet sizes. Nature, 261, https://doi.org/10.1038/261017a0
Huybers, P., & Tziperman, E. (2008). Integrated summer insolation forcing and 40,000-year glacial cycles: The perspective from an ice-sheet/energy-balance model. Paleoceanography, 23(1), http://doi.org/10.1029/2007PA001463
Schoof, C. & Hewitt, I.J. (2013). Ice-sheet Dynamics. Annual Reviews of Fluid Mechanics, 45,http://doi.org/10.1146/annurev-fluid-011212-140 632
Further Information Contact: Richard Katz ([email protected]) Ian Hewitt ([email protected])