Simulating meltwater oxygen isotopes as a proxy for assessing geothermal heat flow in Greenland

Geothermal heat flow is an important control on the dynamics of glaciers and ice sheets. In Greenland however, the exact magnitude and distribution of geothermal heat flow under the ice sheet is largely unknown as only few direct measurements exist at the locations of the deep ice cores. For this reason, several studies have attempted to constrain geothermal heat flow under the ice sheet through various statistical, geophysical, and ice-dynamical modelling efforts. However, many of the different heat flow estimates produced by these models disagree substantially in terms of magnitude and spatial distribution of estimated heat flow values. The oxygen stable isotope composition of ice sheet basal meltwater has so far not been considered in studies of Greenland geothermal heat flow. In this study, we simulate how different estimates of geothermal heat flow affect the production of basal meltwater and its isotopic composition. In our simulations, the modelled δ 18 O values of the basal meltwater show clear and measurable differences between the different model scenarios on the order of a few permille. These results indicate that the spatial configuration of geothermal heat flow is imprinted in the isotopic composition of the subglacial meltwater. We find that transport and mixing of basal meltwater in the subglacial drainage system have substantial influence on the nature of the observed isotope variability such that different sampling locations are sensitive to different aspects of the heat flow distribution in their isotope signal, such as background heat flow magnitude or presence of a central hotspot. The results of our proof-of-concept study suggest that the δ 18 O value of the subglacial meltwater in North-East Greenland is sensitive to magnitude and distribution of geothermal heat flow. Its study could, therefore, be an avenue to improve geothermal heat flow estimates for Greenland and assess the accuracy of existing estimates.