Information on the nature, timing and rates of past environmental change provides a valuable long term perspective for understanding current and future impacts of climate change. Physical, chemical and biological analysis of sedimentary archives help us to build up a picture of both regional climatic variability and local environmental change. The CHERISH project is focusing on sediment sequences which have the potential to provide records of past storm activity, extending back over thousands of years, such as coastal peat bogs, back-barrier lagoons and dune systems.
Radiocarbon dating is based on the principle that all living organisms absorb carbon dioxide during their lifetime, and that after death, a proportion of that carbon which is radioactive (radiocarbon or 14C), decays at a constant rate. By measuring the amount of 14C remaining in plant material, shells or bone, an estimate how long ago that organism was alive can be made. Radiocarbon dating is generally suitable for samples ranging from a few hundred years old up to 50,000 years old, ideally suited to the timeframe under consideration by the CHERISH Project. Advances in analytical techniques mean that very small samples containing as little as 2 mg of carbon can be dated, and it is the most widely used chronological method in palaeoenvironmental studies. Variation in the temporal production of 14C, variance of the proportion of 14C in natural systems, the recycling of “old carbon” by organisms and contamination with younger or older material are all possible sources of error. Therefore it is preferable to date organic material that can be identified such as charcoal, wood and terrestrial plant material, which represent the best choice for 14C analysis of sediments.
Optically Stimulated Luminescence (OSL) Dating
OSL dating utilises the ability of naturally occurring radiation (uranium, thorium and potassium) can get trapped within the crystalline structure of minerals such as quartz and feldspar. The radiation builds up whist the mineral grains are buried in the ground, but released when exposed to sunlight. Samples protected from exposure to daylight are stimulated in the laboratory with light of a particular wavelength to release the stored radiation in the form of light, and by measuring the brightness an estimate can be made as to time the grains were last exposed to sunlight prior to burial. The Aberystwyth Luminescence Research Laboratory (ALRL) in the Department of Geography and Earth Sciences at Aberystwyth University is a world leader in the development and application of luminescence dating methods in environmental and archaeological research.