From precipitation to runoff: stable isotopic fractionation effect of glacier melting on a catchment scale

摘要

Stable isotope variability and fractionation associated with transformation of precipitation/accumulation to firn to glacial river water is critical in a variety of climatic, hydrological and paleoenvironmental studies. This paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central Tibetan Plateau. Isotopic changes are observed by sampling firnpack profiles, glacier surface snow/ice, meltwater on the glacier surface and catchment river water at different times during a melt season. Results show the isotopic fractionation effects associated with glacier melt processes. The slope of the δD-δO regression line and the deuterium excess values decreased from the initial precipitation to the melt-impacted firnpack (slope from 9.3 to 8.5 and average d-excess from 13.4‰ to 7.4‰). The slope of the δD-δO line further decreased to 7.6 for the glacier runoff water. The glacier surface snow/ice from different locations, which produces the main runoff, had the same δD-δO line slope but lower deuterium excess (by 3.9‰) compared to values observed in the firnpack profile during the melt season. The δD-δO regression line for the river water exhibited a lower slope compared to the surface snow/ice samples, although they were closely located on the δD-δO plot. Isotope values for the river and glacier surface meltwater showed little scatter around the δD-δO regression line, although the samples were from different glaciers and were collected on different days. Results indicate a high consistency of isotopic fractionation in the δD-δO relationships, as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale. Copyright © 2013 John Wiley & Sons, Ltd.