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The Southern Ocean exerts a fundamental control on the levels of CO2 in our atmosphere1 and biological productivity across the lower latitude oceans that lie ‘downstream’2. Yet we have little knowledge of how the Southern Ocean’s regulation of atmospheric CO2 or lower latitude biological productivity will operate under warmer-than-modern climates in the future.

The Southern Ocean has two different zones – the Antarctic and sub-Antarctic zones, and they have quite different impacts on ocean biogeochemistry and atmospheric CO2. These contrasts constitute a Southern Ocean ‘biogeochemical divide’3. In the Antarctic Zone, the nutrients important for plankton growth are high at the surface owing to strong upwelling. This enormous amount of unutilized nutrients represents an ‘open window’ through which CO2 currently escapes back to the atmosphere, reducing the efficiency of the global biological pump1. This southern branch consequently has a large impact on atmospheric CO2 (ref.3).

Unutilized nutrients from the Antarctic Zone are carried North by prevailing currents and the strength of nutrient utilization in the sub-Antarctic controls the amount of unutilized nutrients that leak out of the Southern Ocean into lower latitudes2. The sub-Antarctic therefore exerts a direct control on the magnitude of the biological pump in lower latitudes, with major implications for low latitude ecosystems2.

This polar-tropical connection has been shown to operate in the modern ocean2, and is hypothesised to have operated during the last ice age4,5, but we do not know how a warming climate will affect this nutrient leakage from the Southern Ocean. This project will test the efficacy of Southern Ocean-to-low latitude nutrient leakage on orbital timescales, focussing on the warmer-than-modern climates of the early and mid-Pliocene. A variety of palaeoceanographic data hint that the Antarctic CO2 outgassing window may have been more open during Pliocene warmth and that polar-to-tropical nutrient leakage may have been more intense.

The successful candidate will exploit an array of deep-sea sediment sequences recovered by the International Ocean Discovery Program (IODP) across the Southern and tropical Oceans in targeted intervals of the warm Pliocene in order to test the above hypotheses, allowing the candidate to evaluate ocean biogeochemical dynamics during warmer-than-modern climates.

Ocean phosphate concentrations with water depth across an Atlantic transect from the Antarctic (left) to the Arctic (right). Note the plume of nutrient-rich water (red) emanating from the Southern Ocean into the Tropics.


The successful candidate will reconstruct biological productivity in the Southern Ocean and at tropical sites using mass accumulation rates of biogenic opal and biogenic barium. This will be achieved by X-Ray Fluorescence (XRF) scanning to obtain ultra-high resolution analyses of the major and minor chemical element contents of relevant IODP sediment cores. Interpretations of these datasets are typically semi- quantitative so the candidate will use Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) quantitative measurements of absolute Ba (and Al, Fe, Ti, etc) concentrations to calibrate these XRF data. The precise phasing between these polar versus tropical records will be established using orbital-scale correlations between drill sites. Records of d18O, d 13C and Mg/Ca from exceptionally well preserved planktic foraminifera will provide complementary measures of the ventilation state and temperature dynamics of the tropical thermocline – the primary conduit whereby polar oceanographic changes are communicated to the tropics.

Training and Skills

The student will receive training in all aspects of state-of-the-art, high-precision stable isotope (d13C, d18O, trace element) 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 foraminifera from targeted IODP samples. Visit IODP core repository in Bremen to take additional samples from IODP cores and conduct XRF scanning. Training in geochemical analytical techniques, including stable isotope (d13C, d18O, ICP-MS) analyses. Analyse first batches of foraminifer calcite.

Year 2: Continue picking foraminifera from samples & generating XRF and ICP-MS data. Continue generating isotope and trace element data on foraminifera. 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, 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. 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)


Further Details

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:

Applications should be sent to


by 5 pm on Monday 22nd January 2018