A review of various factors influencing the stable carbon isotope ratio of organic lake sediments by the change from glacial to post-glacial environmental conditions

Abstract

A survey is made of various factors influencing the 13 C 12 C ratio of the organic component in lake sediments, focusing on the behaviour at the change from glacial to post-glacial environmental conditions. Increase in the 13C content of the organic sediment is caused by increase in temperature and the corresponding decrease of the supply of molecular CO 2 in the water of the lakes. An increase in the rate of organic production in the lakes may also, perhaps, cause a corresponding 13C increase. An increase of the fermentation of organic mud in the lakes may also have an effect in the same direction. Decrease in the 13C content of the organic sediment is caused by the change of the relative amounts of production of plankton and submersed macrophytes in the lakes from mainly submersed macrophytes to mainly plankton. A decrease towards almost complete absence of bicarbonate and CO 2 originating from carbonate rocks will also lead to a 13C decrease in the organic sediments. The same effect has the change of the terrestrial vegetation cover from almost complete absence to complete cover. A possible decrease of the 13C content in the atmospheric CO 2 has an effect in the same direction.