500,000 years of solar irradiance, climate and vegetation changes

Incoming solar irradiance ultimately governs the amount of energy within the Earth's system. Our understanding of how solar irradiance is modulated by the Earth's orbital pathway underpins our understanding of long-term (>10,000 year) global climate and vegetation change through the geological record. However, there is no independent long-term record empirical record of solar irradiance on timescales >10,000 years. Our proposal is designed to generate the first record of solar irradiance change at the Earth's surface by applying cutting-edge organic geochemical techniques to a unique tropical record of past vegetation change.

Current understanding of solar flux is based upon changes observed in cosmogenic isotopes (10Be and 14C); however, the temporal range over which these techniques can be applied is limited by the half-lives of the respective isotopes. Recent advances in our understanding of pollen/spore chemical composition indicate that a signature of maximum Ultra Violet-B (UV-B) radiation exposure during growth is locked-in, and preserved, within the sporopollenin chemical structure [1]. As UV-B is directly proportional to total incoming solar irradiance this offers an opportunity to extract a long-term record of solar irradiance flux from the fossil pollen/spore record.

During the Quaternary period (last 2.6 million years) orbital forcing has been identified as particularly important in relation to climate and vegetation change associated with glacial-interglacial cycles [2]. However, due to a paucity of appropriate study sites our understanding of terrestrial vegetation change over multiple glacial-interglacial cycles remains limited. New fossil pollen/spore data from a continuous c. 1 million year sedimentary record recovered from Lake Bosumtwi (Ghana), recovered by the International Continental Scientific Drilling Program, provides the first terrestrial record of vegetation change in Africa during this period [3]. The Lake Bosumtwi study site offers an ideal opportunity to assess how solar insolation, climate and vegetation have changed through time because it is well placed to record changes in the global climate system (Inter Tropical Convergence Zone, monsoon) and vegetation (shifts between forest and savannah biome are observed in the fossil pollen record).

We will use Fourier Transformed Infra-Red spectroscopy to analyse the chemical structure of c. 15,000 pollen/spores extracted from 500 different depths (ages) in the Lake Bosumtwi sediment record over the last 500,000 years. By characterizing past change in solar irradiance at the Earth's surface and comparing chemical change with existing model and vegetation data we will provide new insights into the pattern of change. The independent record of solar irradiance will allow climate and vegetation change inferences to be decoupled within the fossil record. Therefore, we will have the potential to determine leads and lags (causality) within the Earth's system, e.g. how do shifts in climate systems related to vegetation change.

The research team have all the requisite skills and experience to deliver the proposal: Gosling (PI OU) has worked on past environmental change in the tropics for 12 years and has worked on Lake Bosumtwi sediments since 2007; Lomax (PI Univ. Nottingham) and Fraser (Res Co-I OU) are organic geochemists who have pioneered research into pollen/spore chemical composition change and its preservation in the geological record. The Centre for Earth, Planetary, Space & Astronomical Research (The OU) will provide the required facilities and research environment.

REFS: [1] Lomax, B.H. et al., Plant spore walls as a record of long-term changes in ultraviolet-B radiation. Nature Geosci., 2008. 1: 592-596. [2] Hays, J.D. et al., Variations in the Earth's orbit: Pacemaker of the ice ages. Science, 1976. 194: 1121-1132. [3] Koeberl, C., et al., The 2004 ICDP Bosumtwi Crater Drilling Project. Meteorit. Planet. Sci., 2007. 42: 483-511.

To ensure effective communication of the proposed research beyond the scientific community the research team have developed the Pathways to Impact and Impact Summary in collaboration with education professional Karen Devine (Education Officer for the British Ecological Society [BES]). The program of impact activity will draw on the expert scientific knowledge of the research team and science communication skills of Karen and other education professionals linked within BES education network. Our overarching impact objective is to deliver science lead educational material based on our research to teachers and students in the UK and Ghana (the country in which our research samples originate from).

WHO WILL BENEFIT FROM THIS RESEARCH?
The primary users will include teachers of science students (12-18 years) and undergraduates. It is intended that identification and targeting of these groups does not exclude other groups or more broad public engagement. The resources and activities developed are intended to ensure greater student engagement with novel research and its application to a real world context. There is significant emphasis (and longer term sustainable impact) placed on training educators of these groups in the UK and Ghana to strengthen understanding of past environmental change and modelling future changes.

HOW WILL THEY BENEFIT FROM THIS RESEARCH?
Four activities will be undertaken to communicate the scientific outputs from this proposal to non-academics.

a) A video of the scientific "learning journey" will be created covering key methodologies and techniques (including field research) to be undertaken by the core research team. The video will be translated, by education professionals, into linked teaching resources suitable for use at a range of levels. The video and resources will be hosted on the education section of the BES website.

b) An educational wall chart will be produced focused on Past Environmental Change related to the proposed research. The content will cover the basic scientific techniques, key scientific concepts, outcomes of the research and remaining scientific questions. The wall chart will be developed with professional designers and educationalists to ensure that the message is communicated clearly. The existing BES educational network will be used to disseminate copies of wall charts free to all secondary schools in the UK and selected institutions in Ghana; in total 10,000 copies of the wall chart will be produced and distributed.

c) Training and capacity building activities will focus on Ghanaian project partners at the Forestry Research Institute of Ghana, including training and provision of equipment to improve herbarium facilities at the Institute. In addition, as part of the personal development of the Researcher Co-I training in media and science communication is planned.

d) To make research progress and findings available to a wide range of people reports will be advertised through the host research groups existing online presence:
- Palaeoenvironmental Change Research Group web pages: http://www.open.ac.uk/science/earthsciences/palaeo/
- Palaeolimnology et al. blog: http://palaeolim.wordpress.com
- @palaeolim twitter feed