Geography lecturer leads ground-breaking project that shines a light on fossil sunshine

Thursday, 15 December 2016

Lake Bosumtwi

An international team of scientists led by Dr Wesley Fraser has reconstructed the longest ever record of past sunshine using fossil pollen grains collected from lake sediments in Ghana, Africa. The study, published today in Scientific Reports, enables us to understand past changes in solar input to the global system over the past 140,000 years. Previously we have had to rely upon computer models to mathematically determine past solar inputs to the Earth.

This work really is a first; being able to peer back in time to understand how the Sun has driven ourglobal system over many of thousands of years is a very exciting prospect

Dr Phillip Jardine, Open University

The Sun is a key component of our natural environment, driving a multitude of processes at Earth's surface, from photosynthesis generating energy within plants, through to global-scale circulation patterns in our oceans and atmosphere. Understanding more about how the Sun has behaved in the past, and the influence this had on Earth's environment, will help scientists predict future climate change.

Dr Jardine used a technique pioneered by one of his co-authors, Dr Wesley Fraser of Oxford Brookes University, to determine past changes in solar input, specifically changes in ultraviolet (UV) radiation. Plants protect themselves from the harmful nature of ultraviolet radiation by incorporating a number of specific chemical compounds into their tissues that absorb and dissipate the energy of UV radiation. Pollen grains of flowering plants are also provided protection by these UV-absorbing chemicals, and thus act as a long-term recorder of ultraviolet radiation from the Sun.

Pollen grains are readily trapped in lake sediments, where they can be preserved for millions of years. By extracting material from Lake Bosumtwi, Ghana, the pollen that was released by flowering plants thousands of years ago can be separated from the lake sediment and chemically analysed for UV-absorbing chemical compounds. It is this chemical signature within the ancient pollen grains that provides us with information about past levels of solar ultraviolet radiation.

“Whatwe have here is a new tool for Earth Science and Geographical research” said Dr Fraser. “The next steps will be to look further back through the fossil recordto try and understand how past changes in UV and solar radiation impacted uponclimate and biodiversity.”

This study is available now at www.nature.com/articles/srep39269

Jardine PE, Fraser WT, Lomax BH, Sephton MA, Shanahan TM, Miller CS & Gosling WD (2016) Pollen and spores as biological recorders of past ultraviolet irradiance. Scientific Reports. DOI: 10.1038/srep39269

Contact: Dr Phillip Jardine (phillip.jardine@open.ac.uk)