Influence of Orbital Forcing on ENSO variability - new insights from an annually laminated speleothem

Lead Research Organisation: Birkbeck College
Department Name: Earth and Planetary Sciences

Abstract

Future climate change scenarios suggest the African continent will become increasingly susceptible to extreme changes in rainfall (droughts and flooding). Attempts to predict rainfall variability in Africa have been limited by our poor understanding of what controls past variability; for example characterising the influence of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on African hydrology. The warmer conditions of the early Pleistocene when the Walker Circulation and ENSO become established offer an analogue to future African climate variability. We propose to investigate these issues by utilising a unique annually laminated half a million year long speleothem deposit from South Africa - the Buffalo Cave flowstone. Building on our previous millennial scale record of African rainfall, we now propose to expand proxy resolution to annual for band thickness and decadal for stable isotopes. The program of annual band thickness counting and stable isotope measurement will generate a rainfall record of unprecedented length and temporal resolution, enabling us to investigate the controls on African rainfall variability at a range of timescales from inter-annual to orbital. The Buffalo Cave flowstone record covers the time period ca. 2.0-1.5 Ma, based on preliminary dating evidence, and crosses one of the most important climate transitions in the Tropics, the intensification of the Walker circulation between 1.8 and 1.7 Ma. We will thus be able to characterise changes in South African rainfall before, during and after the establishment of this fundamental feature of the modern climate system. It will allow us to understand the evolution of the ENSO system and the long term influence of the IOD. This research will provide new insights into rainfall variability in the past, and will aid our predictions of future rainfall in Africa.

Planned Impact

- We will host a workshop on ENSO modelling and palaeodata intercomparison at Birkbeck/UCL in December 2013 with Joy Singarayer (Project Partner). Our work will test a number of hypotheses about the functioning of the tropical climate system, the results of which will need to be disseminated to the wider climate modeling community. This will be a an ideal forum for the dissemination of our results and an opportunity to foster future collaboration with the UK palaeoclimate modelling community.

- We will host a workshop on African Palaeoclimate and human evolution at Birkbeck/UCL in April 2014. This workshop will bring together palaeoclimatologists, palaeoanthropologists and evolutionary modellers to discuss our findings on the causes and consequences of African climate change. Our work will offer new paradigms for the understanding of hominid ecology across a range of timescales from an individual life-span to the origin and extinction of species.

- Research collaboration between the palaeoclimatic and and palaeoanthropological communities in the UK is currently limited. There is an increasing number of young academics working within this field, but there is no infrastructure to support their research. We will address this problem by setting up an interest group to focus on this topic. Researchers at key UK institutions (including Cambridge, Liverpool John Moores, Liverpool University, Oxford, Sheffield, UCL, York and others) will be invited to partake in our networking activities. This will help to increase the profile of UK research within this academic discipline and ensure that it continues to thrive in the future.

- We will set up a web-page for the general public to explain current thinking on the climatic context of human evolution. We will brief the media on the key findings of our research. The Principal Investigator will attend the NERC training course on communicating science to the public.

- This work will be incorporated into poster displays at the local heritage center, giving visitors a feel for the scope of climate change research in the Makapansgat Valley. We will brief local tourist guides on the key findings of our work. Dr Hopley will develop contacts with key South African stakeholders (SAHRA, University of Witwatersrand) and attend the annual University of Sheffield expedition to Makapansgat.

Publications

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Description The research funded on this grant has brought a new understanding of the climate history of Africa and the degree to which future climate change may alter inter-annual rainfall patterns. We have suggested that there is a long-term link between Earth's orbital parameters (insolation) and the variability of southern African rainfall. It is possible that future anthropogenic warming will see a increase in inter-annual rainfall variability and a return to the conditions similar to those experienced by our ancestors 1.8 million years ago. One of the most innovative aspects of this research has been the development of methods for the imaging and counting of long sequences of annual bands in cave deposits (stalagmites and flowstones). Our automated method of confocal microscopy mosaic-building followed by automated band counting enables the rapid counting and measurement of 100,000s of annual bands. This technique is already being used by my academic colleagues and opens up new research questions within the field of palaeoclimatology.
Exploitation Route The research outcomes have had immediate academic and educational impact following publication of the initial results, and will continue to do so as further results are published. It is expected that this will lead to future research into the long-term history of African rainfall variability and wider dissemination through teaching / learning. This research is likely to be taken forward by the environmental sector which is becoming increasingly aware of the likely climate change impacts across Africa. Finally, this work has demonstrated the close ties between human evolutionary change and African climate history with implications for culture and heritage organisations, especially those based in Africa, for whom the shared history of humankind is of political and educational importance.
Sectors Education,Environment,Leisure Activities, including Sports, Recreation and Tourism,Culture, Heritage, Museums and Collections

 
Description This research grant has recently closed. The work was completed successfully and we have published the preliminary findings in Geology; additional publications are to follow. Until additional publications are finalised we can not state the full impact of this research. Beyond the academic impact of this research, we are involved in the promotion/preservation of the natural resources of the Makapansgat Valley, Limpopo Province, South Africa. Our active research program is promoting ecotourism (wildlife/caving/archaeology) within the valley with positive impacts for the local communities and the South Africa heritage agencies.
First Year Of Impact 2011
Sector Education,Environment,Leisure Activities, including Sports, Recreation and Tourism,Culture, Heritage, Museums and Collections
Impact Types Cultural,Economic

 
Description Workshop on Confocal Microscopy for Speleothem Studies
Geographic Reach Multiple continents/international 
Policy Influence Type Influenced training of practitioners or researchers
 
Title Automated Methods in Speleothem Band Counting 
Description This method uses confocal microscopes with an automated stage to build large photomosaics of fluorescent banding in speleothems. This method can image entire speleothems at sub-micron resolution within a few hours. The images are then processed using a Matlab automated band counting and measuring algorithm. This method enables records of annual band thickness to be produced that are orders of magnitude longer than those produced mannually. These new records of annual chronology and rainfall variabilty are enabling new questions to be asked about the interactions between inter-annual and orbital-scale climatic change. 
Type Of Material Improvements to research infrastructure 
Year Produced 2011 
Provided To Others? Yes  
Impact Two grants have been awarded to my colleagues in Austria to use this method on their speleothem samples. They will be visiting my lab in London to undertake the work. 
 
Title Buffalo Cave Flowstone Annual Lamina Dataset 
Description Speleothem annual lamina dataset from Buffalo Cave, Makapansgat Valley, South Africa. Includes annual lamina thickness (microns), lamina count, and age model (Ma, years) for the Early Pleistocene (Lines 1 and 2) and early Holocene speleothems from Buffalo Cave, South Africa. The samples, methods and results are described in full in: Hopley, P. J. et al. (2018) Orbital precession modulates interannual rainfall variability, as recorded in an Early Pleistocene speleothem. Geology. DOI:10.1130/G45019.1. The data is housed at the British Geological Survey (BGS) National Geoscience Data Centre (NGDC). 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact The Buffalo Cave Flowstone dataset is being used by other members of the palaeoanthropological and palaeoclimate communities to test their evolutionary theories and climate models. 
URL http://dx.doi.org/10.5285/59750e40-ac38-4321-ad74-f001a03ebd16