Does fluctuating solar UV-radiation amplify solar forcing of Holocence climatic shifts? Evidence from a new biological proxy in recent and fossil pollen and spores

It is hypothesized that fluctuating solar UV-radiation plays an important role in the amplification of relatively small changes in solar activity that cause major Holocene climate shifts. We have developed a new and very sensitive biological proxy that couples the concentration of stable UV-B absorbing compounds (p-coumaric acid in particular) in the sporopollenin fraction of pollen and spores to the amount of UV-B radiation reaching the Earths surface. This proxy will be used to reconstruct historical UV-B levels during the Holocene and it links these levels with solar activity during periods of abrupt climate change (Preboreal oscillation; transition Subboreal/Subatlantic and climate shifts of the Little Ice Age). Also the p-coumaric acid content of pollen grains and spores from plants of historic herbarium collections (1550-2000) will be analysed. Our approach consists of a) actuo-ecological research (part I) in which the relation of various UV-B radiation levels on p-coumaric acid concentrations are studied in selected plant species (relevant to Part II); and b) paleo-ecological research (Part II) that analyses the fossil record of UV-B in pollen and spores from deposits in relation to evidence for climate change. This approach will be corroborated with other climate proxies such as ?14 C and the local and regional vegetation successions in the same scores. We expect that our study will lead to new insights into solar forcing of Holocene climate change.