Enhanced Antarctic geothermal heat flow derived from defractal spectral analysis of aeromagnetic data: examples from the Thwaites Glacier and Dome C regions

Antarctic geothermal heat flow (GHF) is one of the least constrained basal boundary conditions affecting subglacial hydrology and ice sheet dynamics. Furthermore, the paucity of knowledge about GHF hampers our understanding of the linkages between geodynamic evolution and tectono-thermal conditions in Antarctica.

Here we present the results of enhanced spectral analysis of a new Antarctic aeromagnetic anomaly compilation, conformed at long wavelengths with SWARM satellite magnetic data. We apply manual picking of defractal magnetic power spectra on several different major subglacial lake districts in both West and East Antarctica and compare our results with those obtained using automated workflows implemented in PyCurious. Furthermore, we compare our results with independent GHF estimates from seismology, multivariate-similarity approaches and previous magnetic studies.

We show that in the Amundsen Sea Embayment in West Antarctica manual spectral picking resolves the spatial heterogeneity in GHF anomalies better than automated approaches. We newly define a wide coastal region of relatively lower values corresponding to recently inferred mafic intrusions within this sector of the West Antarctic Rift System and higher GHF in the Byrd Subglacial Basin. This is highly significant as it suggests that elevated GHF may contribute to the onset of enhanced ice flow in the interior of the Thwaites Glacier catchment. Additionally, we find localised GHF anomalies in the area of the Thwaites active lakes that may affect subglacial water availability and promote reduced basal shear stress despite the widespread hard bed conditions related to the occurrence of predominantly crystalline rocks.

In East Antarctica, the manual approach confirms the existence of elevated GHF beneath the Dome C subglacial lake district. However, the anomaly is more linear than previously recognised and better aligned with the trend of major aeromagnetic anomalies interpreted as reflecting extensive Paleo to Mesoproterozoic basement in the sector of East Antarctica. Notably, remarkably similar magnetic anomalies are imaged in formerly contiguous Australia where highly radiogenic igneous provinces significantly enhance GHF.

Overall, we find that the choice of appropriate window sizes and spectral ranges coupled with careful inspection of individual power spectra (including the recognition of outliers) and the choice of defractal parameters is important to better define regional scale heterogeneity in Curie Depth estimates. We also find that incorporating the results of independent seismic, multivariate approaches, and expert knowledge in the geological settings of the different study regions is beneficial to better define the realistic ranges of average Curie Depth and for the conversion from Curie Depth to GHF.

The results of our magnetic studies need to be integrated into thermal modelling frameworks together with the evolving knowledge of crustal and lithospheric properties in Antarctica, including intracrustal heat production and sedimentary basin distribution. This approach will yield improved spatial resolution and accuracy of Antarctic GHF and better understanding of the geological origin and significance of major GHF anomalies.