Contrasting geothermal heat flux provinces unveiled beneath Antarctic subglacial lake districts

Antarctic geothermal heat flux (GHF) is poorly known restricting our ability to assess its influence on subglacial hydrology and ice sheet dynamics. Within the 4D Antarctica and the 3D Earth ESA projects, a new Antarctic aeromagnetic anomaly compilation, conformed at long wavelengths with SWARM satellite magnetic data was complied. All the datasets were levelled, microlevelled and stitched together. We also differentially continued all survey data to 4 km and re-gridded the compilation onto a 4 km grid mesh.

Our new aeromagnetic anomaly compilation enables us to re-assess Antarctic geothermal heat flux (GHF) heterogeneity, a critical basal boundary condition that influences Antarctic ice sheet flow and subglacial melting and hydrology. To estimate GHF we applied Curie Depth Point (CDP) estimation using the centroid, modified centroid and fractal/defractal approaches. We compared our CDP results with independent constraints on crustal and lithosphere thickness derived from seismological, airborne gravity and satellite gravity modelling and effective elastic thickness estimates. We also considered empirical estimates of GHF derived from seismology and recent models of intracrustal heat production from gravity inversion to assess additional uncertainties associated with CDP to GHF conversion. We performed both automated continental scale estimates and nested manual analysis of CDP and GHF with a specific focus on different Antarctic subglacial lake districts.

We found elevated GHF in the West Antarctic Rift System (WARS) beneath the rapidly changing Thwaites (THW) and Pine Island sectors of the West Antarctic Ice Sheet (WAIS) and along the edge of the Marie Byrd Land block. Focussed estimates of GHF were performed over the cascading active lakes beneath THW to provide new constraints for hydrological modelling in this critical sector of the WAIS. We image a large degree of heterogeneity in thermal basal boundary conditions beneath the active subglacial lake districts that underlie the ice streams flowing into the Ross Sea Embayment, which we relate to hitherto poorly known tectono-magmatic segmentation of the WARS.

In East Antarctica, elevated GHF is associated with some of the active lakes underlying the Byrd glacier catchment, but relatively lower GHF values are typical of both the active and static lakes of the northern Wilkes Subglacial Basin (WSB). This suggests limited upper crustal extension beneath this enigmatic subglacial basin compared to major Mesozoic to Cenozoic extension in the WARS. These findings agree with current seismological evidence for well-preserved fast and cold craton margin lithosphere beneath most of the WSB.

We image relatively elevated GHF beneath the Dome C and Dome A subglacial lake districts. This may be caused by cryptic but large-scale provinces of high heat producing Precambrian basement or could reflect major intraplate reactivation of Precambrian fault systems. Elevated GHF is also imaged in Dronning Maud Land and stretching from Enderby Land to Princess Elizabeth Land. We propose that this could reflect Cambrian age lithosphere thinning due to orogenic collapse processes that affected major and yet still cryptic paths of Gondwana-forming orogenic belts fringing East Antarctica. Additionally, Jurassic to Cretaceous thinning was likely superimposed and associated with passive margin formation during Gondwana break-up.