Organic Matter Characteristics in a Changing Permafrost Environment: Yukechi Alas Landscape, Central Yakutia

• Main Author: Windirsch, Torben
• Format: Thesis
• Language: unknown
• Published: 2018
• Subjects: Abalakh; Aldan; Arctic; Talik; Climate change; Ice; Magnetic susceptibility; permafrost; Thermokarst; Yakutia
• Online Access: https://epic.awi.de/id/eprint/48337/; https://epic.awi.de/id/eprint/48337/1/Windirsch_Yukechi_mt.pdf; https://hdl.handle.net/10013/epic.2e1a8ca1-3b83-4d7f-8c7d-9d693370d7dc; https://hdl.handle.net/

With alarmingly fast climate change on global scale, the origin of carbon emissions is becoming more important. Permafrost as one of the largest terrestrial natural storages is among the most relevant carbon sinks that might become a carbon source as air temperatures and snowfall are increasing. This study examines the Yukechi Alas area (N 61.76495° / E 130.46664°), a landscape in Central Yakutia, located on the Abalakh terrace in the Lena-Aldan interfluve). Two drilling cores from different ground types were taken. The comparison of the both cores used in this study also gives insights into the development of permafrost carbon storage. One is a Yedoma core, consisting of material accumulated and syngenetically frozen during the late Pleistocene. The second core was taken from an adjacent alas basin. Alas deposits in this area are altered Yedoma deposits thawed and subsided after lake formation. Both cores cover a timespan of approximately 50 000 years. The cores were analysed for ice content, total carbon and total nitrogen content, total organic carbon content, stable oxygen and hydrogen isotopes, stable carbon isotopes, mass specific magnetic susceptibility and grain size distribution, and were dated using radiocarbon measurements. The laboratory analyses revealed some interesting features that are quite uncommon for Yedoma deposits globally but have been found in Central Yakutia before. The most astonishing finding is the lack of carbon over several meters depth, found in both cores. While in the alas core this could hint on deep thawing during lake-covered stages and large talik formation, and hence decomposition, the same finding in the Yedoma core indicate sediment input of organic-poor material. Water isotope data derived from pore ice show a permanently frozen state of the lower core parts and only represent precipitation water very close to the surface. Therefore, it is unlikely that strong organic matter decomposition took place in this Yedoma core. Also, these core parts consist of more coarse material. Fine sand is found here instead of the silty material that makes up most of the cores. This change in material input was dated to a timespan between 39 000 and 18 000 years before present. During this time, climate experienced variations on a global as well as on a regional scale, which could have influenced the availability of liquid water as well as thaw depth and wind regimes. Especially the changes in wind direction and velocity are likely to have influenced the material composition. The sandy material found is not originating from surrounding areas but could be transported over greater distances. These findings indicate that Yedoma might be more heterogeneous on a global scale than previously thought, making it important to further study Yedoma deposits. Both general carbon content as well as carbon vulnerability, for example due to alternating sediment characteristics within a Yedoma deposit, might be very different. It can be assumed that, before thermokarst processes occured, the core drilled within the alas basin had quite similar characteristics as the Yedoma core. This indicates possible developing characteristics of Yedoma deposits during ongoing climate change. A possible reason for this is increasing lake formation in Arctic areas due to warming air temperatures, which in turn can lead to further carbon release with further permafrost thaw, enhancing a positive feedback cycle in Northern permafrost areas.