ABSTRACT

Detailed measurements of temporal variations in the stable isotopic composition of precipitation and lake water were conducted in the permafrost region near Yakutsk, eastern Siberia. The δ¹⁸O ranged from approximately −30 to −5‰ in precipitation and from −25 to −5‰ in lake water were observed from April to August, 2000. Temporal changes in δ¹⁸O of precipitation observed weekly at 12 sites all showed the same trend. The temporal variation of δ¹⁸O in lakes classified into two groups: isotopically steady-state lakes with less than 5‰ variation, and non-steady-state lakes with variation exceeding 10‰. In non-steady-state lakes, the water originated from snowmelt, and the δ¹⁸O of lake water gradually enriched as a result of evaporation during the summer. In steady-state lakes, the water originated predominantly from ¹⁸O-enriched lake water that had evaporated in the previous summer. The temporal volumetric and isotopic variations in alas lakes are accurately depicted by an isotope mass-balance model using Rayleigh fractionation over daily time steps. The inflow of soil water (subsurface flow) was estimated to be constant (200 m³/day) from May to August, based on the difference between observed and simulated lake volumes. Taking the isotopic mass-balance into consideration, the soil water in lower part of the active layer is inferred as a major component of inflow which has a δ¹⁸O of about −23‰.