Test of an equal taxon-weight modification of Middeldorp's pollen density dating on data from varved sediments of Lake Gosciaz, Poland

The cores from the varved sediments of Lake Gosciaz enable testing of metho ds, based on pollen concentration, to reconstruct the time-basis of a palyn ological data set. The sediments' varves or annual laminae were counted and their thicknesses measured, and the pollen content was recorded at known i ntervals with regard to depth and time. In the present study, we have treat ed this pollen record as if the sediments were not annually laminated and a s if, consequently, the time-basis of the pollen record was unknown. We rec onstructed several different time-bases by means of two methods using polle n concentration, namely pollen density dating (PDD) according to Middeldorp and a modification of that method, which gives all included arboreal polle n-taxa the same weight. equal taxon-weight modification (ETW). After recons tructing these time-bases we compared them with the varve time-basis. We co nclude that both PDD and ETW result in goad time-bases. Our modification im proves the performance of Middeldorp's method, largely because of the use o f spline interpolation instead of a polynomial regression of varve age on p ollen variables. An advantage of ETW over PDD is that ETW using a spline pr oduces a good approximation of arboreal influx, preserving both trends and short-term variability, whereas PDD results in an arboreal influx being an unnaturally smooth function of time. (C) 1999 Elsevier Science B.V. All rig hts reserved.