Isotope hydrology (2H and 18O) of Ikka fjord and its tufa columns, SW Greenland

From 1995 to 2022, several expeditions have visited the small Ikka fjord in SW Greenland to study growth and stability of the more than 1000 submarine tufa columns build of the metastable, cold-water carbonate ikaite (CaCO3·6H2O). The different water types in the area have been sampled for geochemical and stable isotope (2H and 18O) investigations. Here we present the results of more than 300 isotope analyses of water from the fjord and from streams, lakes, springs and tufa columns. Fjord water samples identify a two-component mixing system (R2 > 0.99) between freshwater runoff and sea water entering from the Davis Strait. The fresh water samples have an average composition of –95.4‰ δ2H and –13.1‰ δ18O. We f ind both seasonal and altitude effects in fresh water related to early (June–July) or late (August) sampling time. All freshwater samples excluding lakes but including previous precipitation data (GNIP, 1963–1974) can be described by a Local Meteoric Water Line with slope of 6.43 ± 0.12 and offsets between 6.34 and 6.56. Column water samples are mixed with fjord water but extrapolation to a chlorine-free composition defines an endmember composition of –102‰ δ2H and –14.2‰ δ18O. These composi tions identify precipitation on top of the igneous plateau at ~ 500 m altitude as the source for the column water.