The Antarctic Circumpolar Current (ACC) flows clockwise unimpeded around Antarctica and is the greatest ocean current on Earth (Fig. 1). The geographic separation of South America from Antarctica and subsequent formation of Drake Passage are thought to have removed the final obstacle to continuous circumpolar flow, thereby initiating the ACC and thermally isolating Antarctica from the wider global ocean. This isolation is assumed to have been crucial in Cenozoic climatic cooling2-4 because the ocean around Antarctica supplies the abyss with ‘new’ deep waters that spread globally. The timing of Drake Passage formation and ACC initiation is controversial2-4, ranging from the late Oligocene to the middle Eocene, a time span of 18 Myr, with uncertainties regarding the onset of shallow versus deep ACC circulation. But this project will determine whether these existing estimates have all underestimated the age of onset. A potential onset at the very start of the Cenozoic cooling trend is suggested by an eightfold increase in seafloor spreading rates that accompanied a change in spreading direction between South America and Antarctica 50 Myr ago5, along with tantalising features in a variety of palaeoceanographic data.
The successful candidate will exploit an array of deep-sea sediment sequences recovered by the International Ocean Discovery Program (IODP) across the Southern and Atlantic Oceans in a targeted, key interval of the Eocene in order to test for an early opening of Drake Passage and associated ACC onset. Results will allow the candidate to reconstruct ocean circulation patterns, ocean chemical structure and carbon cycling, providing additional vital contributions to efforts to understand Earth system dynamics during extreme greenhouse warmth.
The successful candidate will reconstruct Southern and Atlantic Ocean palaeo-circulation evolution using neodymium isotope (eNd) analyses of the fluorapatite of fish teeth1 and of postdepositional Fe-Mn oxide coatings precipitated on planktonic foraminifera1, both providing monitors of water mass source and flow pathways. Benthic foraminifer d13C records will provide a complementary measure of the ventilation state of abyssal water masses. Drill sites will be correlated to each other at the timescale of orbital cycles using i) existing high resolution d13C records, ii) new d13C records from bulk carbonate and benthic foraminifera, 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. These datasets will also allow a test of the sensitivity of ocean circulation to orbital forcing.
Training and Skills
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. The student will be encouraged to participate in an IODP drilling expedition.
Other skills developed include scientific communication through writing, poster and oral presentations to academic and non-academic audiences, and online teaching opportunities via the Open University Virtual Learning Environment, including teaching on the new Massive Open Online Courses (MOOCs).
NERC CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes.
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, foraminifer coatings and foraminifer calcite.
Year 2: Continue picking fish teeth and foraminifer from samples & generating eNd data. Continue generating d13C data on foraminifera and bulk carbonates for inter-site correlations. 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. Present results at international conference. 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)
The project offers extensive opportunities for the student to interact and collaborate with international scientists involved in complementary research. Results from this project will complement other datasets of Eocene temperature and pCO2 that are currently being produced by a large NERC-funded multi-institution consortium project (value £2.5M) that, together, will transform our understanding of climate and ocean circulation during Eocene warmth. This project will also use 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 and Kochi (Japan), involving collaboration with a team of scientists at Bremen.
Beyond the Supervisory team, key ongoing project collaborators are:
Prof. Ursula Röhl & Thomas Westerhold (astronomical age model construction, XRF core scanning; Bremen, Germany)
Prof. Tina van de Flierdt & Howie Scher (eNd analyses of fish teeth and postdepositional Fe-Mn oxide coatings; Imperial College, UK & South Carolina, USA)
Students should have a strong background in Earth science and enthusiasm for oceanography. Experience of geochemistry is desirable. The student will join a well-established team researching palaeoceanography at the Open University.
Please contact Philip Sexton (Philip.Sexton@open.ac.uk) for further information.
Applications should include:
- a cover letter outlining why the project is of interest and how their skills match those required,
- an academic CV containing contact details of three academic references
- a CENTA application form, downloadable from: http://www.centa.org.uk/media/1202/centa-studentship-application-form.docx
- and an Open University application form, downloadable from: http://www.open.ac.uk/students/research/sites/www.open.ac.uk.students.research/files/documents/Application%20form.docx
Applications should be sent to
by 5 pm on Monday 22nd January 2018