Pliocene palaeoclimate off SE Africa: Insights from IODP Expedition 361

It has been suggested that East Africa has undergone strong aridification between 3-5 million years ago as a consequence of changes in the source water distribution through the Indonesian seaway into the Indian Ocean [deMenocal, 1995; Cane and Molnar, 2001]. Results from an ocean circulation model showed that the northward displacement of New Guinea, about 5 Myr ago, may have switched the source of flow through Indonesia from warm South Pacifc to relatively cold North Pacifc waters. In the modern climate there is a strong link between east African rainfall and Indian Ocean SST, with warmer temperatures associated with more rain [Goddard and Graham, 1999]. Assuming that the modern ocean circulation system worked in a similar way in the Pliocene, the consequence of a tectonically driven northward move of New Guinea would have caused a reduction in sea surface temperatures in the Indian Ocean ultimately leading to reduced rainfall over eastern Africa.
Why is it important to study climate changes in East/southeast Africa over that time period? We all come from Africa. We know that major steps in the evolution of African hominids and the emergence of the genus Homo in East Africa occurred in the Pliocene [Bobe and Behrensmeyer, 2004]. These developments seem to fall into times of major global and regional climatic changes especially with shifts to more arid, open environmental conditions in Africa near 2.8 Ma [deMenocal, 1995]. The change from humid to more arid conditions in East Africa has been linked mainly to remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles[deMenocal, 1995]. Here, however, we want to test if instead a cooling in the southwest Indian Ocean temperature due to a change of water through the archipelago of Indonesia drove changes in East and southeast Africa rainfall variability.

In order to build a more coherent picture of the evolution of African rainfall variability, long high-resolution records documenting subtropical South African climate variability are essential but currently lacking. Future climate change projections from the latest phase of the Coupled Model Intercomparison Project suggest that severe droughts will impact South Africa by the end of the 21st Century, due to changes in the Hadley Circulation and increased surface temperatures, with potentially significant consequences for that region [Collins et al., 2013]. Palaeoclimate reconstructions provide evidence of past long-term and abrupt climate variability in East and South Africa and can provide an important test-bed for validating such model predictions.

Moreover, the here proposed study will provide an important archive of past climate changes within the Pliocene which, when considered in combination with archaeological records, can provide evidence for the potential link between climate and the origin of the divergence of hominins from the apes to the origin of the Homo clade. The link between climate, population growth/settlement and innovation is also important for us today. While recurrent shifts between long-term droughts and humid phases in East and South Africa during the Pliocene-Pleistocene arose from natural causes, climate models project that this region will undergo progressive aridification in the future as part of a general drying and poleward expansion of the subtropical dry zones driven by the human-induced rise in Greenhouse gases [Collins et al., 2013].

Our findings shall be disseminated to academics via conference presentations and publications in peer reviewed journals.

Aside from academic beneficiaries, this research could also benefit the general public.

Informing the general public about climate systems is important as an informed public may make lifestyle/business-model changes accordingly as well as prompt governmental policy change through democratic processes. Spurring public interest in climate science, or science in general, particularly in schools, could encourage more people to pursue careers in research as well as encourage a healthy appetite for scientific discovery.
We will make our work known to the public through outreach events and school visits. Cardiff University organises regular activities showcasing our research, either to undergraduates or the general public in open-door events. Deep-sea drilling operations and the scientific results yielded from such drilling remain a popular and frequent topic for such events and the results from this work could easily form a part of such outreach. Schools in the Cardiff area also regularly welcome workshops, educating students about climate/ocean science. We will ensure that our work, if appropriate, is promoted in such ways wherever possible by contacting those in charge of existing events or by organising new outreach events.


Museums:
We have close collaborations with National Museum Wales, based in Cardiff, and we will discuss potential joint outreach activities based on this research. The links with both geology and archaeology make this ideally suited for a temporary exhibition, as National Museum Wales has both a geology department an an archaeology department with links to Cardiff University.