Holocene climate change in high latitudes recorded by stable isotopes in peat

Abstract: A key to the understanding of natural and human induced climate variations is to reconstruct past changes from different environments. No outstanding method for general use has been pinpointed, instead, a need of multi-proxy studies is often stressed and the reconstructions are under constant improvement by new techniques. The aim of my PhD project is to test a relatively new method, stable carbon and oxygen isotopes isolated from single moss species, and develop climate reconstructions based on them. The main interest is to implement the method in records from northern peatlands where permafrost conditions prevail, and contribute to the discussion about the warming Arctic. The first part of the Licentiate thesis is a method study about the variation of stable carbon and oxygen isotope ratios in different moss plant components. Modern isotopic values were calibrated against instrumental climate records from the study region in west-central Canada. The impact of peat decay on proxies was investigated by colorimetric and chemical (C/N) methods. The results indicate that the isotope signal is well preserved in peat that started to accumulate c. 6000 years ago. Furthermore, statistical analyses imply that the variation of stable carbon isotope ratios in Sphagnum fuscum is significantly correlated to the variation of summer temperatures. A temperature reconstruction was developed in the second part of the thesis, based on stable carbon isotope ratios. Wet/dry periods were derived from the stable oxygen isotope record, macrofossil analysis, and the peat humification record. The results were compared with other proxy records from the vicinity of the study area. The main climate periods, such as The Mediaeval Warm Period and The Little Ice Age were registered in the temperature record. The amplitude of the temperature change was similar to especially those in chironomid based reconstructions, showing c. 6.5±1°C variation in July temperatures during the past 6.2 ka.