Supplementary material to "Biogeochemical evolution of ponded meltwater in a High Arctic subglacial tunnel"

Abstract

Supplementary Methods S1: Water isotope fractionation modelA model was developed using the principles of isotopic fractionation to estimate the isotopic composition of incremental ice, incremental vapor, and residual water as a hydraulically isolated waterbody progressively freezes and evaporates. Natural waters are composed of hydrogen, which has two stable isotopes ( 1 H and 2 H or deuterium, D) and oxygen, which has three stable isotopes ( 16 O, 17 O and 18 O). H2O molecules in natural water can therefore have one of nine possible molecular weights. Due to differences in the vibrational energies of the bonds of these molecules, the freezing of water under equilibrium conditions results in heavier molecules fractionating more readily into the solid ice, while lighter molecules fractionate more readily into the remaining liquid water. During evaporation, lighter molecules fractionate more readily into the vapor, leaving the residual water relatively enriched in the heavier molecules.