Magnetotelluric Constraints on Upper Mantle Viscosity Structure and Basal Melt Beneath the Greenland Ice Sheet

Abstract

<p>Mass loss from the Greenland Ice Sheet has accelerated during the past decade due to climate warming. This deglaciation is now considered a major contributor to global sea level rise, and a serious threat to future coastlines. It is therefore vital to measure patterns and volumes of ice sheet mass loss. However, measurements of the ice sheet’s mass and elevation, both of which decrease as the ice melts, are also sensitive to ground deformation associated with glacial isostatic adjustment (GIA), which is the solid Earth’s response to ice loss since the last ice age. For Greenland, GIA is poorly constrained in part because Greenland’s complex geologic history, with a passage over the Iceland Plume, probably created large lateral viscosity variations beneath Greenland that complicate the GIA response.</p><p>The Norwegian MAGPIE project (Magnetotelluric Analysis for Greenland and Postglacial Isostatic Evolution) seeks to develop new constraints on mantle viscosity beneath Greenland by collecting magnetotelluric (MT) data on the ice sheet. MT images the Earth’s electrical conductivity, which is sensitive to three of the major controls on mantle viscosity: temperature, partial melt content and water content of solid-state mantle minerals. We therefore plan to use MT data, together with existing seismic data, to map viscosity variations beneath Greenland. During the summer of 2019 we deployed 13 MT stations in a 200 km grid centered on EastGRIP camp on the North-East Greenland Ice Stream. Good quality data were recorded at periods up to 10,000 s, providing good resolution of upper mantle conductivity structure. We also collected a broadband MT traverse across the NE Greenland Ice Stream, which allows us to directly compare MT and radar data to investigate the role of basal melt on ice flow dynamics. During the 2020 summer season we will be collecting additional data over the south-western and central parts of the ice sheet. Here we show preliminary constraints on the conductivity of the asthenosphere, lithosphere, and crust beneath Greenland, which will be used to investigate the upper mantle viscosity structure, including the present-day signature of the Iceland Plume.</p>