Pollen accumulation values and delta 13C ratios in peat reflect high-frequency variations in summer temperature.
by
Sheila Hicks
University of Oulu, Finland
Coauthors: Keith Bennett (Uppsala University, Sweden), Danny McCarroll (University of Wales, Swansea, U.K), Neil Loader (University of Wales, Swansea, U.K)

A new method is demonstrated for reconstructing summer temperature at a near annual resolution from Sphagnum fuscum peat cores. This involves the analysis of pollen accumulation rates (grains cm-2 year-1) and stable carbon isotope content of very thin (2mm) consecutive peat slices. The method is applied to a core from Kevo in the far north of Finland. The locality is within the mountain birch woodland zone where pine occurs as isolated islands beyond its forest limit. Under such conditions pine is particularly sensitive to climate change. A modern data training set of annual pollen deposition monitored in a standardized way for the period 1982-2000 at 14 different localities in northern Fennoscandia is used. The pollen assemblages (which include the whole range of taxa) characterize the different vegetation belts in which they are being deposited. However, calibration of the annual variations in pollen deposition with local meteorological data shows that pollen deposition in general, and that of pine pollen in particular, is controlled by the summer temperature of the year before pollen emission. Additional factors are spring frosts, and wind speed and direction at the time of pollen emission. The Kevo peat profile is dated by ²¹⁰Pb measurements on consecutive 1cm thick slices. The model based on these results is used to convert the pollen concentration in the 2mm slices to a record of pollen accumulation at near annual resolution, thus enabling a reconstruction of temperature variations. Stable carbon isotope ratios, measured from picked Sphagnum leaves, also at 2mm intervals, are correlated with these pollen accumulation values, though there is an offset, probably because delta¹³C responds to the temperature of the current summer rather than that of the previous year. The delta¹³C values from the peat are, additionally, compared with similar measurements from the latewood cellulose of securely dated pine tree rings from the same area and with local meteorological data. This procedure, though still experimental, may provide a link between high-resolution peat profiles and long, absolutely-dated, tree ring chronologies.

Date received: March 30, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cagc-75.