Jeffery J. McDonnell C. Kendall P.V. Unnikrishna 2002 <p><span>Isotopic variations in melting snow are poorly understood. We made weekly measurements at the Central Sierra Snow Laboratory, California, of snow temperature, density, water equivalent and liquid water volume to examine how physical changes within the&nbsp;snowpackgovern&nbsp;meltwater&nbsp;</span><i>δ</i>¹⁸<span>O. Snowpack samples were extracted at 0.1</span><span>&nbsp;</span><span>m intervals from ground level to the top of the snowpack profile between December 1991 and April 1992. Approximately 800</span><span>&nbsp;</span><span>mm of precipitation fell during the study period with&nbsp;</span><i>δ</i>¹⁸<span>O values between −21.35 and −4.25‰. Corresponding snowpack&nbsp;</span><i>δ</i>¹⁸<span>O ranged from −22.25 to −6.25‰. The coefficient of variation of&nbsp;</span><i>δ</i>¹⁸<span>O in snowpack levels decreased from −0.37 to −0.07 from winter to spring, indicating isotopic snowpack homogenization. Meltwater&nbsp;</span><i>δ</i>¹⁸<span>O ranged from −15.30 to −8.05‰, with variations of up to 2.95‰ observed within a single&nbsp;snowmeltepisode, highlighting the need for frequent sampling. Early snowmelt originated in the lower snowpack with higher&nbsp;</span><i>δ</i>¹⁸<span>O through ground&nbsp;heat flux&nbsp;and rainfall. After the snowpack became isothermal, infiltrating snowmelt displaced the higher&nbsp;</span><i>δ</i>¹⁸<span>O liquid in the lower snowpack through a piston flow process.&nbsp;Fractionation&nbsp;analysis using a two-component mixing model on the isothermal snowpack indicated that&nbsp;</span><i>δ</i>¹⁸<span>O in the initial and final half of major snowmelt was 1.30‰ lower and 1.45‰ higher, respectively, than the value from simple mixing. Mean snowpack&nbsp;</span><i>δ</i>¹⁸<span>O on individual profiling days showed a steady increase from −15.15 to −12.05‰ due to removal of lower&nbsp;</span><i>δ</i>¹⁸<span>O snowmelt and addition of higher&nbsp;</span><i>δ</i>¹⁸<span>O rainfall. Results suggest that direct sampling of snowmelt and snow cores should be undertaken to quantify tracer input compositions adequately. The snowmelt sequence also suggests that regimes of early lower&nbsp;</span><i>δ</i>¹⁸<span>O and later higher&nbsp;</span><i>δ</i>¹⁸<span>O melt may be modeled and used in catchment tracing studies.</span></p> application/pdf 10.1016/S0022-1694(01)00596-0 en Elsevier Isotope variations in a Sierra Nevada snowpack and their relation to meltwater article