Unveiling the lithospheric and mantle dynamic controls on Antarctic topography
Accurately constraining past and future ice sheet evolution requires a better understanding of boundary conditions for ice sheet models. Two key factors - topography and heat flux - are both in part influenced by spatially and temporally variable mantle dynamics. This study uses an interdisciplinary approach to probe the present-day crust and mantle beneath Antarctica. First, observed bathymetry and topography in the oceanic and continental realms are corrected for isostatic effects to isolate the residual topographic signal as a proxy for dynamic support. In this way, a comprehensive suite of oceanic residual depth and continental residual elevation anomalies are calculated. This compilation includes the addition of 487 newly interpreted multichannel seismic lines in the Southern Ocean, and new receiver function analysis for 15 stations in the northern Transantarctic Mountains. A novel joint modelling approach, integrating high-frequency receiver functions and P-wave coda autocorrelation, is used to constrain ice and subglacial properties. Subsequently, inversion of low-frequency receiver functions reveals crustal velocity structure, refining estimates of bulk crustal thickness and density, as required for residual elevation calculations. All resulting residual depth and elevation measurements are integrated into previously published global databases to present a smoothed global spherical harmonic representation of the data. While high spherical harmonic degrees (l = 40) effectively capture oceanic swells in mantle support, their significance to continental residual elevation remains limited by data uncertainty. Nevertheless, spatial patterns of inferred dynamic topography in the continental and ocean realms are consistent with upper mantle (<300km) shear wave velocity anomalies, long-wavelength free-air gravity anomalies, regions of thinned lithosphere, and Neogene intraplate basaltic volcanism. Modelling of rare earth element concentrations from these volcanic provinces defines melt fraction as a function of depth, allowing for both mantle potential temperature and lithospheric thickness to be constrained. Results are consistent with geophysical observations and reinforce understanding that regions of upwelling mantle act to thin the lithosphere and elevate topography. Steeper geothermal gradients associated with regions of plate thinning and volcanism have significant implications for the delivery of heat to the base of the Antarctic Ice Sheet. The high average elevation of East Antarctica, however, is attributable to buoyancy induced by lithospheric depletion, acting to thermally insulate the cratonic region from mantle processes. Collectively, these observations highlight the role of mantle-lithosphere interactions in Antarctica and the subsequent importance of accounting for how convective processes have shaped topography through time.
Antarctica, Mantle Dynamics, Dynamic Topgraphy, Geodynamics, Seismology
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