Seasonal variation in stable isotopic composition of alas lake water near Yakutsk, Eastern Siberia

摘要

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 delta(18)O ranged from approximately -30 to -5parts per thousand in precipitation and from -25 to -5parts per thousand in lake water were observed from April to August, 2000. Temporal changes in delta(18)O of precipitation observed weekly at 12 sites all showed the same trend. The temporal variation of delta(18)O in lakes classified into two groups: isotopically steady-state lakes with less than 5parts per thousand variation, and non-steady-state lakes with variation exceeding 10parts per thousand. In non-steady-state lakes, the water originated from snowmelt, and the delta(18)O of lake water gradually enriched as a result of evaporation during the summer. In steady-state lakes, the water originated predominantly from O-18-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 m(3)/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 delta(18)O of about -23parts per thousand. [References: 16]