date: Fri, 03 Apr 1998 16:02:58 +0200 from: Håkan grudd subject: Dropstones and tree rings to: k.briffa@uea.ac.uk Keith, I have just been listening to a very interesting seminar on dropstones from caves in South Africa and Gotland (Island east of Sweden). Both are works by graduate students. In the African dropstone annual varves have been identified and crosdated with tree rings. The width of the varves correlate with annual precipitation (semiarid climate) and tree-ring width. The maximum gray tone in each varve has been correlated with temperature. The correlation values for the calibration period is very good! The student presented a temperature curve for the last c. 6500 years. It looks really interesting: a generally warm period in the first part, drops down to generally lower vaules at around 2000 BC, a big peak centered around 400 BC! Little bit varmer with a lot of variability in Medieval times, a drop in 14th century with cold temperature and very little variation for some hundreds of years (Little Ice Age?) and the again higher in the last two centuries. The dropstone from Gotland had dating problems. They tried to crossdate with Bartholin's pine chronologies without success. Karin Holmgren, who has been supervising this work and herself made her thesis on dropstones and climate, have very little knowledge in dendro-methods and seeks co-operation. The world seems filled with prospects! Do you know anything about tree-ring chronologies from north-eastern South Africa? Cheers, Håkan PS. Any luck in finding my keys?