Airborne investigations are a keystone for understanding the Antarctic environment across many scientific disciplines. Over the past decade and more, the use of drones has been proposed as a means to enhance this airborne capability. Small quadcopter/multi-rotor drones, typically flown within visual line of sight, have become a well-established and routinely deployed technology. However, larger fixed-wing uncrewed aerial vehicles (UAVs) capable of beyond-visual-line-of-sight missions similar to traditional crewed aircraft have not been routinely deployed. Here, we report on the first deployment of a large (10 m wingspan) UAV for scientific data collection from Rothera Research Station, Antarctica. The platform, a Windracers Ultra, flew 2978 km over 25 missions, collecting a range of scientific observations including visual and hyperspectral imagery, atmospheric turbulence data and gravity and magnetic data. All science missions were carried out beyond visual line of sight and were up to 2.25 h/260 km long. Missions included coordination with and operation alongside crewed aircraft. Our field season has successfully demonstrated that large UAVs can play a significant role in Antarctic data collection, working alongside crewed aviation to improve our understanding of Antarctica.

Heterogeneities in subglacial geology and crustal properties can play a major role in determining the boundary conditions at the crucial interface between the solid earth and the cryosphere in Antarctica. Geothermal heat flow, a parameter closely tied to regional geology, can particularly influence the behaviour of the overriding icesheet. However, direct geological samples which could inform understanding of heat flow and other geological parameters are limited to ice free regions along the coast, high mountain ranges or isolated nunataks, while the origin of geological material transported by glaciers themselves is often ambiguous. Geophysical joint inversion of gravity and magnetic data can therefore play a key role in constraining the geological and crustal properties of the rocks hidden beneath the ice.We present a 3D crustal model of Wilkes Subglacial Basin and Transantarctic Mountains based on joint inversion of airborne gravity and magnetic data using the “Variation of Information” inversion algorithm incorporated in the software JIF3D. The applied “Variation of Information” technique enforces a coupling in the objective function between inverted susceptibility and density distribution during the inversion. The objective function is minimized iteratively until a reasonable mismatch between observed and inverted data is reached. The coupling ensures that identical geometries in the inverted density and susceptibility distribution are found relating to shared gravity and magnetic sources. This technique provides an enhanced inversion result for interpreting subglacial geology since inverted geometries relate to both petrophysical quantities compared to separately inverting for density and susceptibility distributions.Our model reveals a large body located in the interior of Wilkes Subglacial Basin interpreted as a batholithic intrusive structure, as well as a linear dense body at the margin of the Terre Adélie Craton. Density and susceptibility relationships of the anomalous bodies, together with their shapes in 3-dimensions are used to inform the composition and the origin of these crustal bodies. Comparing the density and susceptibility values recovered by our inversion with measurements on Antarctic rock samples indicates that the postulated batholitic intrusion is granitic in composition, but distinct from the Granite Harbour Igneous Complex described previously in the Transantarctic Mountains area. Emplacement of such a large volume of intrusive granite can potentially elevate local geothermal heat flow significantly, due to relative concentration of radiogenic heat producing elements such as U, K and Th. Finally, we present a new conceptual tectonic model for the region based on the inversion results, which includes passive margin development ~670 Ma, with the emplacement of the batholith intrusion before the Granite Harbour Suite.

The Antarctic Peninsula is a unique sector of the circum-Pacific continental margin arc where subduction ceased due to a series of ridge-trench collisions, preserving a relatively un-deformed magmatic arc. This region, therefore, has the potential to provide key insights into how subduction systems behave during their final stages. However, the remote nature of the region means that both geological and geophysical data coverage is often sparse, limiting the ability to interpret its tectonic evolution. Here we present a new analysis of gravity and magnetic data collected from a Windracers Ultra Uncrewed Aerial Vehicle (UAV). The survey targeted a 75 x 25 km region where the Antarctic Peninsula bends and magnetic signatures change, which has been attributed to the onshore influence of adjacent oceanic transform faults running approximately orthogonal to the Peninsula. Using joint inversion of magnetic and gravity data based on a "Variation of Information" approach, we show the region is dominated by two large intrusions, of likely granodiorite composition. Our data indicate little evidence for structural control on magma emplacement, however, coincident imagery suggests that after magma emplacement the region was subject to significant deformation approximately parallel to the Peninsula margin. We interpret these features in terms of the processes occurring as subduction ceased.

Magnetic data collection in Antarctica is commonly carried out using airborne platforms, which allow to cover large spatial areas. Airborne surveys in Antarctica have been conducted since the 1950s as part of international and collaborative efforts. A challenge in creating a homogenous magnetic data compilation for Antarctica arises from heterogeneity in data collection through the decades, for example from different flight lines spacing, different observation height and long time period between surveys. Traditional data processing is performed manually or semi-automated which is time consuming due to the factors described above.Equivalent source technique is a powerful tool to automate the data processing to combine irregular airborne surveys on different observation heights and time periods. The magnetic field data from different airborne surveys can be represented by a set of equivalent sources that accurately reproduce the input data. The magnetic forward response of the equivalent sources can be calculated at any height making upward / downward continuation obsolete and allowing a uniform observation height between surveys. Furthermore, the magnetic field can be calculated on a regular grid, removing irregular flight lines from airborne data compilations. Combining the equivalent source method with despiking-, wavelet filtering-, IGRF/DGRF correction- and weighted distance base station correction routines allow a fully automated processing workflow to create a harmonised magnetic compilation containing irregular airborne surveys with decreased noise.We present a test case in East Antarctica to highlight the potential of an automated processing workflow to harmonise magnetic airborne data without biases arising from manual processing. Here, we utilise ICECAP data (2009-2017) and RAE data (1956-1960) as well as the ADMAP data compilation grid as prior. The next step is to use ADMAP line data to create a fully automated homogeneous continent wide Antarctic magnetic data compilation under the SCAR ADMAP working group umbrella.

Subglacial geology remains largely unknowns in Antarctica. Direct geological samples are limited to ice free regions along the coast, high mountain ranges or isolated nunataks, while the origin of geological material transported by glaciers themselves is often ambiguous. 3D singular and joint inversions of airborne gravity and magnetic data recovers subsurface density and susceptibility distribution. The relationship between both inverted petrophysical quantities provide crucial insight for subglacial geology and rock provinces interpretations. Validation of indirect derived subglacial geology models are critical but very challenging in Antarctica due to the sparsity of rock samples. We present 324 new density and susceptibility measurements on rock samples from Northern Victory Land, East Antarctica. 251 samples have been measured at the National Polar Sample Archive (NAPA) from the Federal Institute for Geosciences and Natural Resources (BGR) in Berlin-Spandau, Germany and additional 73 samples were measured at the BGR in Hannover, Germany. We use the petrophysical measurements to validate our recent regional scale 3D joint inversion model of the Wilkes Subglacial Basin and the Transantarctic Mountains. Furthermore, we validate inversion results on a local scale of singular magnetic inversion based on high resolution airborne magnetic data with a flight line spacing of 500m in the Mesa Range. We demonstrate that we can provide reliable discrimination between Ferrar Dolerites, Kirkpatrick Basalt and Granite Harbour intrusion rocks based on our local inversion model and that the recovered susceptibilities agree with those measured at rock samples from the study area. Furthermore, we show that regional scale inversion model of gravity and susceptibility distribution agrees for samples of the dominant crustal rock types. However, densities of small-scale dense intrusion bodies like Ferrar Dolerites are underestimated by the regional scale inversion, while the susceptibility range is correctly recovered. Constraining subglacial geology with joint inversion of airborne potential field data is heavily depended on the resolution of the airborne survey, flight line coverage, the inversion scale, and the scale of the target feature. Regional scale inversion is adequate for large scale geological heterogeneities, which underestimate petrophysical quantities for small scale structures, while local scale inversions are able to resolve such structures but are more computational demanding and in the case of Antarctica lack ultra-high resolution airborne gravity data with a line spacing below 1000 – 500m.

Direct geological information in Antarctica is limited to ice free regions along the coast, high mountain ranges or isolated nunataks. Therefore, indirect methods are required to reveal subglacial geology and heterogeneities in crustal properties, which are critical steps towards interpreting geological history. We present a 3D crustal model of density and susceptibility distribution in the Wilkes Subglacial Basin and the Transantarctic Mountains (TAM) based on joint inversion of airborne gravity and magnetic data. The applied “variation of information” technique enforces a coupling between gravity and magnetic sources to give an enhanced inversion result. Our model reveals a large-scale body located in the interior of the Wilkes Subglacial Basin interpreted as a batholithic intrusive structure, as well as a linear dense body at the margin of the Terre Adélie Craton. Density and susceptibility relationships are used to inform the interpretation of petrophysical properties and the reconstruction of the origin of those crustal blocks. The petrophysical relationship indicates that the postulated batholitic intrusion is granitic, but independent from the Granite Harbour Igneous Complex previous described in the TAM area. Emplacement of a large volume of intrusive granites can potentially elevate local geothermal heat flow significantly. Finally, we present a tectonic evolution sketch based on the inversion results, which includes development of a passive continental margin with seaward dipping basalt horizons and magmatic underplating followed by two distinct intrusion events in the Wilkes Subglacial Basin with Pan-African ages (700 - 551 Ma) and Ross ages (550 - 450 Ma).

Summary Bedrock geology from Antarctica remains largely unknown since it is hidden beneath thick ice sheets. Geophysical methods such as gravity and magnetic inverse modelling provide a framework to infer crustal rock properties indirectly in Antarctica. However, due to limited availability of rock samples, validation against direct geological information is challenging. We present a new rock property catalogue containing density and susceptibility measurements on 320 rock samples from northern Victoria Land. This catalogue is used to assess the reliability of local and regional scale inverse results, including a new local high resolution magnetic inversion in the Mesa Range region and a previously published regional scale joint inversion of gravity and magnetic data in northern Victoria Land and the Wilkes Subglacial Basin. We compare our density and susceptibility measurements to global and local measurements from the literature to access the correlation to rock types and geological units. Furthermore, the measured values are compared against inverted values. The close correspondence between inverted and measured rock properties allows us to predict locations of rock types where currently such information is missing. The utility of measured susceptibility and density relationships for interpreting inversion output provides a strong incentive to incorporate local rock samples into geophysical studies of subglacial geology across Antarctica.

The Transantarctic Mountains (TAMs) separate the warmer lithosphere of the Cretaceous‐Tertiary West Antarctic rift system and the colder and older provinces of East Antarctica. Low velocity zones beneath the TAM imaged in recent seismological studies have been interpreted as warm low‐density mantle material, suggesting a strong contribution of thermal support to the uplift of the TAM. We present new Curie Point Depth (CPD) and geothermal heat flow (GHF) maps of the northern TAM and adjacent Wilkes Subglacial Basin (WSB) based exclusively on high resolution magnetic airborne measurements. We find shallow CPD and high GHF beneath the northern TAM, reinforcing the hypothesis of thermal support of the topography of the mountain range. Additionally, this study demonstrates, that limiting spectral analysis to areas with a high density of aeromagnetic measurements increases the resolution of CPD estimates revealing localized shallow CPD and associated high heat flow in the Central Basin of the WSB and the Rennick Graben (RG). Across the study area the CPD ranges from 15 to 35 km and the GHF values range from 30 to 110 mW/m 2 . The recovered CPD range is compatible with recent Moho depth estimates, as the CPD predominantly lies within the crust, rather than in the magnetite‐poor mantle. GHF estimates, based on the CPD estimates, show a good agreement to sparse in situ GHF measurements and the location of active volcanoes. Comparison to existing continent‐wide GHF estimates shows strong differences from magnetically‐derived heat flow estimates, while seismologically‐derived heat flow estimates show the best agreement to our results.

The Wilkes Subglacial Basin hosts potentially the largest unstable sector of the East Antarctica Ice Sheet due to the depth of the ice bed below sea level. Ice covering such basins poses a potentially high, but poorly constrained risk for future sea-level rise, as it is more vulnerable to melting by warming of the surrounding ocean. Such melting could potentially trigger mechanisms of unstable retreat. The neighbouring Transantarctic Mountains are the largest non-contractional mountain range on Earth. Traditionally, the Transantarctic Mountains are viewed as dividing the ancient East Antarctic craton from the younger West Antarctic Rift system. However, petrological samples and previous geophysical mapping suggest that the craton boundary is further west, following the western edge of the Wilkes Subglacial Basin. Subglacial geology influences geothermal heat flow and bed roughness, and therefore to better understand the past, present and possible future behaviour of the East Antarctic Ice Sheet improved understanding of the subglacial geology on which it flows, especially in the Wilkes Subglacial Basin and Transantarctic Mountains region, is important.We present a new 3D crustal model of the Wilkes Subglacial Basin and the Transantarctic Mountains based on joint inversion of airborne gravity and magnetic data using the mutual information inversion algorithm incorporated in the software JIF3D. Our model shows a large intrusive body located in the interior of the Wilkes Subglacial Basin and suggests a tectonically complex area west of the Basin, which could potentially indicate the transition zone at the margin of the Terre Adélie Craton. Geological units are inferred by clustering of inverted susceptibility and density distribution and are validated against sparse petrological samples from the Transantarctic Mountains region and along the George V Land and Terre Adélie coasts. Our inferred crustal properties model can provide crucial insight into the heterogeneity of subglacial geology in terms of thermal conductivity and crustal heat production, which could influence the geothermal heat flow in this area and therefore make the overlying ice sheet more vulnerable than commonly thought.

In this study, we present an estimate of the gravity signal of the slabs beneath the Alpine mountain belt. Estimates of the gravity effect of the subducting slabs are often omitted or simplified in crustal-scale models. The related signal is calculated here for alternative slab configurations at near-surface height and at a satellite altitude of 225 km. We apply three different modelling approaches in order to estimate the gravity signal from the subducting slab segments: (i) direct conversion of upper mantle seismic velocities to density distribution, which are then forward calculated to obtain the gravity signal; (ii) definition of slab geometries based on seismic crustal thickness and high-resolution upper mantle tomography for two competing slab configurations – the geometries are then forward calculated by assigning a constant density contrast and slab thickness; (iii) accounting for compositional and thermal variations with depth within the predefined slab geometry. Forward calculations predict a gravity signal of up to 40 mGal for the Alpine slab configuration. Significant differences in the gravity anomaly patterns are visible for different slab geometries in the near-surface gravity field. However, different contributing slab segments are not easily separated, especially at satellite altitude. Our results demonstrate that future studies addressing the lithospheric structure of the Alps should have to account for the subducting slabs in order to provide a meaningful representation of the geodynamic complex Alpine area.

The Wilkes Subglacial Basin in East Antarctica hosts one of the largest marine-based and hence potentially more unstable sectors of the East Antarctic Ice Sheet (EAIS). Predicting the past, present and future behaviour of this key sector of the EAIS requires that we also improve our understanding of the lithospheric cradle on which it flows. This is particularly important in order to quantify geothermal heat flux heterogeneity in the region. The WSB stretches for almost 1600 km from the Southern Ocean towards South Pole. Like many intracratonic basins, it is a long-lived geological feature, which originated and evolved in different tectonic settings. A wide basin formed in the WSB in a distal back arc basin setting, likely in response to a retreating West Antarctic Paleo-Pacific active margin from Permo-Triassic times. Jurassic extension then led to the emplacement of part of a huge flood basalt province that extends from South Africa to Australia. The region was then affected by relatively minor upper crustal Mesozoic to Cenozoic(?) extension and transtension, producing narrow graben-like features that were glacially overdeepened, and presently steer enhanced glacial flow of the Matusevich, Cook and Ninnis glaciers. Here we present the results of our enhanced geophysical imaging and modelling in the WSB region performed within the 4D Antarctica project of ESA, which aims to help quantify the spatial variability in subglacial Antarctic geothermal heat flux (GHF), one of the least well constrained parameters of the entire continent. We exploit a combination of airborne radar and aeromagnetic data compilations and crustal and lithosphere thickness estimates from both satellite and airborne gravity and independent passive seismic constraints to develop new geophysical models for the region. To help constrain the starting models, including depth to basement beneath the Permian to Jurassic cover rocks, we applied a variety of depth to magnetic and gravity source estimation approaches from both line and gridded datasets. Given the huge differences between recent satellite gravity estimates of crustal thickness (Pappa et al., 2019, JGR) and sparse seismological constraints, we examine different scenarios for isostatic compensation of Rock Equivalent Topography and intracrustal loads, as a function of variable effective elastic thickness (Te) across the WSB and its flanks. Our models reveal a major lithospheric-scale boundary along the northeastern margin of the WSB, separating the Ross Orogen from a cryptic and composite Precambrian Wilkes Terrane. At the onset of enhanced flow for the central Cook ice stream, we image a Precambrian basement high with a felsic bulk composition. We suggest based on the similarity in potential field signatures that it represents late Paleoproterozoic to Mesoproterozoic igneous basement as exposed in South Australia, where it also associated with high GHF (80-120 mW/m2), primarily caused by anomalously radiogenic granitoids. We hypothesise that the differences in basement depth and metasediment/sediment thickness, coupled with differences in intracrustal heat production give rise to significantly greater heterogeneity in GHF beneath different sectors of the WSB than previously recognised. To help quantify such heterogeneity we develop a suite of new probabilistic thermal models for the study region.