Pollen deposition rates in peat and lake sediments from the Pinus sylvestris L. forest-line ecotone of northern Norway

Abstract

A comparative investigation of pollen deposition in peat and limnic sediments from the Pinus sylvestris-Alnus incana forest line in Dividalen, central Troms, northern Norway was performed by pollen analyses of sub-modern sediments. The possibilities of using 210Pb and 137Cs-datings in calculations of pollen influx in peat and limnic sediments are discussed. Correlation between the lead–cesium peat chronology and a marker-based limnic chronology is achieved at AD 1945–1946 by comparing the percentual pollen-curves. The upper 14 cm of the peat and 12 cm of the limnic sequence are hence supposed to represent the period ca. 1945–ca. 1996. The mean percentual representation of Pinus pollen is nearly twice as high in the peat sediments as in the limnic sediments, probably due to a slight over-representation from pine trees at the edge of the mire. The mean percentual pollen values for Alnus and Betula pubescens-type is fairly equal in peat and lake sediments, while the pollen influx rates are higher for all tree taxa in the lake sediments. This may be caused by the lake being exposed to a larger regional component than the smaller and topographically more sheltered mire. To achieve reliable pollen influx data at a near annual resolution, one needs a good control of the sedimentation processes, close intervals of isotope measurements and additional chronostratigraphically fixed marker horizons.