Lake initiation and ecosystem change: A paleoenvironmental reconstruction from sedimentary records in Goldstream Valley, Alaska

Global warming has a direct impact on the degradation of permafrost and the resulting ground subsidence. Thermokarst lakes develop. During the formation of thermokarst lakes, the thawing of permafrost releases methane and carbon, which was locked in the frozen ground before. As a result, the generation of thermokarst lakes is directly linked to climatic changes. The aim of this research is to reconstruct the initiation of lakes which are situated in the discontinuous permafrost of Goldstream Valley, Central Alaska. In course of an expedition in summer 2017, cores from eleven thermokarst lakes were taken from Goldstream Valley in Central Alaska. The samples were analysed for sedimentological and biochemical parameters. Additionally, macro remains were examined. There are three classes of thermokarst lakes within this research: Lakes which develop over a longer period of time and lakes which developed in less time. The third class includes lakes where the initiation phase was not caught within the selected transition zones, but it is assumed they also developed over a longer period of time and therefore belong to class one. A distinct peat layer is characteristic for lakes of class one. The analysed macro remains reflect the degree of degradation of the sediment except in one case. In case of biochemical analyses, the macro remains are only partly reflected. An implication of thermokarst lake development is a release of a high amount of methane and carbon dioxide while thermokarst lakes develop. So, the more time a lake needs to originate, the higher the emissions of methane and carbon dioxide are. Lakes that form within less time therefore emit less methane and carbon dioxide