Microscale spatial variability of snowpack: isotopic and chemical heterogeneity of a firn pack at Qomolangma (Mount Everest), central Himalaya

For a better understanding of snow metamorphosing processes and more precise snow- ice-core interpretations, it is necessary to know the extent of microscale spatial variability of isotopic and chemical distributions in a snowpack. This work presents an investigation on the horizontal heterogeneity of the isotopic and chemical distributions in a firn pack on East Rongbuk Glacier at Qomolangma (Mount Everest), central Himalaya. One pit wall of 1.2 � 1.2 m 2 at 6520 m a.s.l. was sampled at intervals of 10 cm in a matrix pattern with a total of 144 samples collected. All the samples were analyzed for d 18 O and ionic concentrations. Small horizontal isotopic and large chemical heterogeneities were found. The averaged coefficient of variation (CV) of the twelve 10 cm thick layers for d 18 O is 0.052, and in the whole snow thickness of 120 cm it is 0.016, which is in the range of analytic precision and thus indicates complete homogeneity. However, the ionic distribution shows considerable heterogeneity. The averaged CV values of the 10 cm thick layers for ionic concentrations vary in the range 0.628-1.477 depending on the ions. Based on these CV values, the heterogeneity sequence is: Mg 2+ > Ca 2+ > K + > Na + > Cl - > SO4 2- > PO4 3- > NO3 - > NH4 + . The averaged CV values for all the ions, except for NH4 + , decrease with increasing snow thickness, although the decreasing rates and extents are different. However, the CV values of different ions are still large and in the range 0.183-1.116 when the snow thickness increases to 120 cm. The heterogeneity sequence becomes: K + > Mg 2+ > Ca 2+ > NH4 + > Na + > Cl - > PO4 3- > NO3 - > SO4 2- . The CV average change with thickness is different for NH4 + . From 20 to 100 cm it increases slightly with increasing thickness, but all the values are lower than the average of 10 cm thick layers.