The meridional overturning circulation (MOC) comprises planetary-scale oceanic ﬂows that are of direct importance to the climate system because they transport heat, salt and nutrients meridionally and regulate the exchange of CO2 with the atmosphere2. The MOC, and in particular, the Atlantic’s MOC, is now known to have responded very sensitively to orbital forcing across the Pleistocene glacial cycles and played a crucial role in driving Earth into, and out of, these glacials2. Models predict that the Atlantic’s MOC could weaken, shoal, or even disappear, in response to ongoing global warming, with profound consequences for regional climate change.
Man-made CO2 emissions are projected to elevate atmospheric concentrations of this greenhouse gas to levels that, by the end of this century, will be higher than at any time since the climatic ‘greenhouse’ of the Eocene epoch (55 to 35 million years ago)1. Yet there are no existing geological data with which to determine whether an Atlantic MOC even existed during the early Eocene greenhouse or how any MOC may have differed from its modern counterpart, let alone its potential sensitivity to, or role in driving, climatic change at orbital to secular timescales3.
The successful candidate will exploit an array of deep-sea sediment sequences recovered by the Integrated Ocean Drilling Program (IODP) across a broad latitudinal Atlantic Ocean transect in a targeted, key interval of the early Eocene in order to achieve the Project Highlights above. Results will be integrated with numerical modelling experiments currently being run at the Open Uni. (by Neil Edwards) to ground-truth the model and further evaluate the controls on ocean circulation during greenhouse warmth.
The successful candidate will reconstruct the nature of the Atlantic MOC, and its sensitivity to orbital forcing, using neodymium isotope (eNd) analyses of the fluorapatite of fish teeth4 and of postdepositional Fe-Mn oxide coatings precipitated on planktonic foraminifera4, both providing monitors of water mass source and flow pathways. The sortable silt grain size index will provide a complementary measure of the flow vigour of deep-sea currents. Drill sites will be correlated to each other at the timescale of orbital cycles using i) existing high resolution d13C records3, ii) new d13C records from bulk carbonate, iii) X-Ray Fluorescence (XRF) scanning to obtain ultra-high resolution analyses of the major and minor chemical element contents of relevant IODP sediment cores.
Training and Skills
CENTA students will be provided with 45 days training from CENTA through their PhD which includes a 5-day residential and a 10-day work placement. In the first year, students will undertake training in general environmental science, research methods and core skills as a single cohort. Training in years 2 and 3 will progress from core skills to masterclasses specific to the project and overall scientific theme.
The student will receive training in all aspects of state-of-the-art, high-precision stable isotope (d13C, d18O, eNd) analyses in world-class geochemical laboratories. Training will also be provided in non-destructive, ultra-high resolution analyses of the major and minor chemical element contents of IODP sediment cores, and in the sortable silt grain size method from Dr Alex Dickson at Oxford. Parallel datasets (e.g. benthic foraminifer d13C, d18O, trace element ratios, etc) will be generated by other project partners for synthesis with doctoral researcher’s data. There may also be opportunity for the student to participate in an IODP drilling expedition.
Year 1: Training in clean laboratory protocols and processing of sediment samples. Picking fish teeth from targeted IODP samples. Visit IODP core repository in Bremen to take additional samples from IODP cores. Training in geochemical analytical techniques, including stable isotope (d13C, d18O, eNd) analyses. Analyse first batches of fish teeth, bulk sediment leachates and bulk carbonates.
Year 2: Continue picking fish teeth from samples & generating eNd data. Continue generating d13C data on bulk carbonates for inter-site correlations. Analyse sortable silt samples. Visit Bremen for additional XRF core scanning datasets. Construction of astronomically calibrated age models. Two weeks placement for additional skills (HEI/non-HEI). Process & interpret data and prepare manuscript #1.
Year 3: Finish remaining analytical work, continue data processing and interpretation. Visit two international conferences to present results. Prepare manuscripts #2 and #3. Possible opportunity for involvement in IODP expedition. Write up PhD thesis. Contribute to wider IODP synthesis efforts.
Partners and collaboration (including CASE)
Project results will help meet the ambitious scientific goals of IODP Exp. 342 (comprising some of the target sequences), and the successful candidate will have opportunities to interact and collaborate with IODP Exp. 342 scientists. Results from this project will also complement other datasets of Eocene temperature and pCO2 that are currently being produced by a large multi-institution consortium (http://descentintotheicehouse.org.uk) that, together, will transform our understanding of Eocene climate and ocean circulation.
This project will also utilise non-destructive, ultra-high resolution analyses of the major and minor chemical element contents of sediment cores using the X-Ray Fluorescence (XRF) sediment core scanners at Bremen, involving collaboration with a team of scientists at Bremen.
Beyond the Supervisory team, key project collaborators are:
Prof. Heiko Pälike, Ursula Röhl & Thomas Westerhold (astronomical age model construction, XRF core scanning; Bremen, Germany)
Dr Sandra Kirtland-Turner & Prof. Andy Ridgwell (Numerical modelling of ocean circulation during extreme climatic warmth and its response to hyperthermal events; UC Riverside, USA)
Students should have a strong background in, and enthusiasm for, Earth science, oceanography and/or chemistry. The student will join a well-established team researching Earth system processes during past warm climates at the Open University and Oxford.
Please contact Philip Sexton (firstname.lastname@example.org) for further information.