Size, distribution and evolution of thermokarst lakes in Central Yakutia, Russia

Abstract:

The permafrost landscape of Central Yakutia is subject to rapid modifications as a result of intensive land use, extreme weather, and the current global warming. With regard to the predicted increase in precipitation and temperature due to climate change, quantitative knowledge of the small-scale variability of active thermokarst processes is required. Here, we analyzed size and frequency distribution of lakes >0.1ha on different geomorphological ice-rich permafrost terraces east of Yakutsk using Landsat 8 data and we mapped the change of thermokarst and alas lakes since 1944 at the Yukechi study site using historical airborne and current satellite data and analyzed growth rates and thaw subsidence. Generally, larger lakes in higher frequency are dominating lower and younger terraces, while higher and older terraces are dominated by smaller lakes. In particular, smaller lakes in less density are distributed on older and more ice-rich terraces while the younger and less ice-rich terraces are characterized by highest lake densities and larger lakes. Remote sensing analysis at the Yukechi study site indicate that lake-level changes of residual alas lakes during the past 70 years were mainly affected by the winter precipitation and the annual water balance. In the meanwhile, extensive agricultural use in the post-war period led to the disturbance of the thermal and hydrological balance of the permafrost and results in rapid and sustained growth of young thermokarst lakes on undegraded ice-rich permafrost deposits. Climatic parameters, however, are affecting only growing rates within certain time periods. The mean growth rate of all mapped thermokarst lakes at Yukechi is 0.8 ±0.6 m a^-1, with a mean thaw subsidence of 7.0 ±1.6 cm a^-1. Our results indicate that topography, geomorphology, and surficial cryolithology are important controlling factors on the distribution of lakes. Furthermore, thermokarst activity is influenced by climatic parameters but it is accelerated by anthropogenic land use. Further studies of multi-temporal images are necessary to validate these results.