Hydrology, geochemistry and Sr isotopes in solids and solutes of the meltwater from Mittivakkat Gletscher, SE Greenland

This study was initiated to investigate elemental fractionation and Sr isotope systematics associated with glacial erosion by direct comparison of particulate and dissolved load in glacial runoff. Discharge measurements along with chemical and Sr isotope investigations were carried out at the Mittivakkat Gletscher (Glacier), Ammassalik Ø, Southeast Greenland. Major bedrock types are the Ammassalik Intrusive Complex (AIC) of mafic composition and garnet–granite gneiss (GGG) of acidic composition. Mechanical denudation rates (1 mm a−1) reflected in the major outflow are in the range of temperate valley glaciers in Norway. Chemical denudation rates (32 t km−2 a−1) and estimated rates of CO2 drawdown by silicate weathering (720–100 kgC km−2 a−1) are low compared to global mean and match values measured for High Arctic glaciers on Svalbard. The contrast in chemical and Sr isotope composition of bedrock makes Sr isotope ratios a powerful tool for determining source areas of solid and dissolved load. High Ca/K ratios in water compared to suspended particulate matter (SPM) indicate faster dissolution of Ca minerals. By contrast, in GGG bedrock, where biotite and K-feldspar are abundant, Sr isotope ratios in solutes are higher than in SPM, supporting preferential release of 87Sr from a K-mineral lattice.