Climate and Atmospheric Science (ICAS) PhD Projects
Ocean Circulation in a Warmer World
Supervisors: Dr Alan Haywood, Dr Bridget Wade Dr Harry Dowsett (United States Geological Survey) Collaborators: Prof. Paul Valdes (University of Bristol), Dr Marci Robinson (United States Geological Survey), Dr Christina Riesselman (United States Geological Survey)
Background and Rationale The mid-Pliocene Warm Period (mPWP ~ 3 million years before present) has been described by the Intergovernmental Panel on Climate Change (IPCC) as a potential analogue for a future greenhouse gas induced global warming. Climate model-predicted global annual mean temperatures are ~2 to 3 ºC higher than today (Figure 1). At this time the position of continents, faunal and floral types, and ocean bathymetry were the same as, or very similar to, present-day, with CO2 concentrations in the atmosphere similar to projected mid 21st Century levels.
The excellent geographical distribution of geological sample sites, abundant geological material suitable for dating and a precise stratigraphy serves to make the mPWP an ideal time interval in which to investigate ‘warm period’ climate processes and feedbacks. Numerous data and palaeoclimate modelling studies have examined the potential cause(s) of the warmth of the mPWP. Geological data and model predictions indicate a large warming of the surface ocean in the Atlantic and further north in to the Nordic Seas and the Arctic compared to modern conditions. Therefore, a current focus of research is the behaviour of the ocean circulation, specifically the production of deepwater and vigour of thermohaline circulation during this the last great interval of global warmth in Earth’s history.
The US Geological Survey’s PRISM Group (Pliocene Research Interpretations & Synoptic Mapping) are developing comprehensive data sets for deep ocean temperature and chemical composition of water masses to further elucidate the behaviour of ocean circulation as a driving mechanism of global warmth during the mPWP.
Aim
We wish to integrate new state-of-the art palaeoceanographic data sets with equally state-ofthe- art numerical model predictions of ocean behaviour so that together the palaeoceanographic and numerical modelling communities can move towards an enhanced understanding of the role the oceans played in sustaining a critical period of global warmth in Earth history.
Key Science Objectives Determine how well a leading IPCC-class climate model is able to reproduce patterns of ocean temperature and circulation change reconstructed for the mPWP, and understand why the model predicts these changes. This will be achieved by:
1) The diagnosis of predictions of ocean temperature and circulation patterns from a fully coupled-ocean atmosphere General Circulation Model (HadCM3L), already set up for the mPWP, to determine the degree of agreement with geological proxy data
2) Performing new simulations with HadCM3L with a new oxygen isotope tracer scheme enabled allowing the prediction of the O18/O16 content of the oceans. This will facilitate a more direct comparison between geological data and model outputs circumventing the need to make assumptions regarding the translation of geochemical data into ocean temperatures. Changes to the model conditions will be made incrementally (from the modern situation to the Pliocene) facilitating the identification of which boundary condition changes have most effect on ocean circulation.
Integrate existing and new point-based reconstructions of ocean temperature and chemical composition into a full global scale simulation of ocean circulation and temperature properties of the mPWP. This will be achieved by:
1) Performing new HadCM3 and HadCM3L simulations constrained by sea surface and deeper ocean temperature estimates provided by the PRISM Group and allowing the model to come into full equilibrium with these conditions.
Science Plan
In Phase 1 the student will analyse a suite of existing climate model experiments for the mPWP using the Hadley Centre coupled ocean-atmosphere model, in which the predictive ability of the model will be explored. In Phase 2 the student will perform new simulations using an oxygen isotope enabled version of the climate model in order to better diagnose the response of ocean circulation and how well the model fits PRISM reconstructions. These simulations will also enable the student to understand which initial conditions within the model have most effect on the model-predicted temperature and circulation changes for the mPWP. In Phase 3 the student will perform further simulations with the climate model constrained by the latest PRISM geological reconstructions of ocean temperature (both surface and deep ocean).
Training
Based within the Sellwood Group for Palaeo-Climatology (http://homepages.see.leeds.ac.uk/~sgpc) the PhD will provide a board spectrum of training in analytical methods used in palaeoceanographic reconstruction and climate modelling equipping the student with the skills necessary to become the next generation of global change scientist, capable of contributing to understanding and predicting past and future climate change. Specifically, the student will be trained in coupled ocean-atmosphere modelling gaining considerable IT and programming skills. The student will attend the NERC Earth System Science and Urbino Summer School (in Italy) to broaden his/her understanding of Earth Systems Science and palaeoclimatology, and will have the opportunity to undertake a variety of postgraduate training workshops at the University of Leeds. The student will also benefit from a close link with the US Geological Survey and will visit the USGS PRISM group each summer to facilitate the integration of the modelling and data collection effort.
Further Reading
Haywood, A.M. & Valdes, P.J. (2004), Modelling Middle Pliocene Warmth: Contribution of Atmosphere, Oceans and Cryosphere. Earth and Planetary Science Letters, 218, 363-377.
Haywood, A.M., Valdes P.J., Hill D.J., Williams M. (2007), The mid Pliocene Warm Period: a test-bed for integrating data and models, In: M. Williams, A.M. Haywood, J. Gregory and D. Schmidt (ed), Deep-time perspectives on climate change: marrying the signal from computer models and biological proxies, The Micropalaeontological Society Special Publications The Geological Society of London.
Dowsett, H.J. (2007), The PRISM palaeoclimate reconstruction and Pliocene sea-surface temperature. In: M. Williams, A.M. Haywood, J. Gregory and D. Schmidt (ed), Deep-time perspectives on climate change: marrying the signal from computer models and biological proxies, The Micropalaeontological Society Special Publications The Geological Society of London. 459-480.