Antarctica

Antarctica hosts the largest ice sheets on Earth, and 98% of the continent is buried underneath. The lithospheric structure is however still poorly explored. Robust knowledge of the interior is essential to understand the Earth’s response to ice mass changes (glacial isostatic adjustment).

Of particular interest are the depth and geometry of the main subsurface boundaries (Pappa et al., 2019), which are the interface between crustal and mantle rocks (Moho discontinuity) and the base of the rigid tectonic plate (lithosphere). Since both of them are accompanied by changes in rock density, we used gravimetric data from the GOCE satellite to build a 3D model of Antarctica’s deep structure. By also taking into account the rock composition according to temperature and pressure, the model is internally consistent, which helps to compensate the scarcity of robust ground and airborne data in Antarctica. From the temperature distribution in our model, we derive present-day solid Earth’s behavior due to glacial isostatic adjustment, one of the most significant uncertainties when assessing present-day ice sheet mass change from satellite studies.

 

A new Moho depth map of the Antarctic continent based on satellite gravity gradient data. In areas that are covered by seismic stations, our estimates match the seismological crustal thickness assessments to a large extent. Previously under-explored regions of East Antarctica are now mapped in unprecedented detail. ASB=Aurora Subglacial Basin, DML=Dronning Maud Land, EL=Enderby Land, GSM=Gamburtsev Subglacial Mountains, IAAS=Indo-Australo-Antarctic Suture, LG=Lambert Graben, TAC=Terre Adélie Craton, TAM=Transantarctic Mountains, VD=Valkyrie Dome, WSB=Wilkes Subglacial Basin.

 

Video: Ice coverage, bedrock topography, Moho depth, and lithospheric thickness of Antarctica. The colours represent temperatures in the lithosphere based on our modelling. Note the strong contrast between thin and warm West Antarctica (left) and thick and cold East Antarctica (right).

 

The hereby established lithospheric structure and temperature model also serves as an input for geodynamic modelling, investigating the plausibility of a mantle plume in West Antarctica - a hypothesis that has been discussed interdisciplinary for more than 30 years. In particular, we use the mantle convection code ASPECT to estimate the impact of a potential plume ponding beneath the lithosphere on the surface heat flux beneath the ice sheet. Testing various plume parameters, our reference plume model influences the lithosphere-asthenosphere boundary (LAB) over a distance of about 1000 km and generates an uplift of maximum 25 km, in agreement with previous plume models (e.g. Bredow et al., 2017).

 

Lithosphere thickness with thermal anomaly beneath central Marie Byrd Land, simulating a potential plume beneath West Antarctica (a) and the effect of the plume on the LAB in a vertical cross-section (b).

The regional case studies of Antarctica are continuously compared and reconciled with the global reference model established in the course of the 3D Earth project. We will also further exploit the new airborne compilation ADMAP2.0 to fill the polar map present in satellite data. Moreover, this lithospheric model of Antarctica will be used as a background model for the inversion of aero gravity data in order to delineate different geological regions beneath the ice coverage.