TOUCHED BY MAN: BIVALVE SHELLS (MARGARITIFERA MARGARITIFERA, L.) AS ARCHIVES FOR ANTHROPOGENIC FORCING OF THE CLIMATE

Evaluation of the effects of logging on freshwater ecosystems could greatly benefit from long-term biomonitors. As of yet, freshwater bivalves such as Margaritifera margaritifera (> 280 years) from Fennoscandia, are the only known multi-proxy archives capable of reconstructing the history of terrestrial ecosystems. In addition, shell records of freshwater bivalves can bridge the gap between terrestrial archives such as trees and marine archives.

Through the analysis of variations in annual shell growth and stable isotopes (C, O) from 24 freshwater pearl mussels from three localities in Fennoscandia we investigated the effects of deforestation, fires, liming and fertilization on limnological systems. Results suggest that shells record changes in temperature, food supply, pollution and precipitation. The time span (1801-1999) covered by this work provides the opportunity to discriminate between natural climatic oscillations and anthropogenic influences. For example, increased growth rates (> 600%) during the mid 1980s were caused by fertilization and liming. Fires and logging lead to an increased influx of nutrients after 1940, as revealed by decreasing δ¹³C values. Besides these human-induced changes, traces of quasi-decadal oscillations such as the NAO (North Atlantic Oscillation Index) or the NATP (North Atlantic Sea Surface Temperature Tripole Index) are well preserved in the shells. Our study demonstrates by sclerochronological methods and geochemistry that the freshwater pearl mussel is an ideal tool for reconstructing anthropogenic forcing of the climate during the youngest Holocene.