AbstractWe investigate the impact of combining Gravity Field and Steady‐state Ocean Circulation Explorer (GOCE) satellite gravity anomaly and Bedmap2 terrain relief data to enhance Antarctic seismic Moho estimates over the satellite's coverage region south of latitude 60°S. The study considers improving the seismic surface wave‐inferred AN1 Moho (An et al., 2015a, https://doi.org/10.1002/2014JB011332) from misfits of the gravitational effects of the terrain and the seismic Moho computed at 250 km altitude. The updates also relate the GOCE gravity anomalies that correlate directly and inversely with the terrain's gravity effects as isostatic anomalies of the uncompensated mantle relief. These terrain‐correlated effects infer potential isostatic adjustments of the Moho that may help constrain the crust's stress field, track the Gamburtsev Subglacial Mountains to the Kerguelen mantle hotspot, and further test the putative Wilkes Land impact basin for its crustal attributes. Analysis of the gravity‐updated seismic AN1 Moho (sAMoho) estimates suggests that most are within the seismic errors of several kilometers or less. However, the gravity‐updated estimates that are deeper than the sAMoho estimates tend to characterize anomalously hot upper mantle where the assumed mantle‐to‐crust density contrast may be too low. These Moho difference estimates discern elevated heat flow for the Maud Rise, Kerguelen Plateau, Pacific‐Antarctic Ridge, and most of western Antarctica extending from the Pacific‐Antarctic Ridge along the Transantarctic Mountains and across the Ross Sea through Marie Byrd Land and the western margin of the Antarctic Peninsula Microplate to the Scotia Ridge. The methodology of this study also is effective in updating any Moho model for improved gravity and terrain data.

By using ground source heat pumps to exchange heat with the shallow surface, areas with minimal or no tectonic activity can still be viable resources for low-temperature geothermal energy. This study focuses on generally characterizing the potential exploitation of flooded mines as low-temperature thermal resources within Ohio. These unconventional thermal resources offer large, thermally stable bodies of water, which store relatively more heat than saturated soils and bedrock. The legacy of underground mining, predominantly in the southeastern and eastern portions of Ohio, makes ground source heat pump geothermal energy a potentially valuable resource for the state. Using geographic information system (GIS) software, mines that were either flooded or partially flooded and within 1.6 km of a population center were selected as potential candidates for ground source heat pump exploitation. Physical and thermal parameters were calculated for each of the identified geothermal sites. These include: maximum and minimum residence times of waters within the mines, maximum and minimum recharge to the mines, effective mine volumes, linear groundwater velocities, groundwater flow direction, and percentage of the mine that is flooded. The total theoretical amount of heat extraction or addition per degree change in mine water temperature (Celsius degree) was calculated for each identified mine site, as well as the potential amount of heat either entering or being dissipated in mine waters due to groundwater recharge.This study identified 147 possible mine sites spanning 21 counties that might be used for ground source heat pump installations in Ohio. The mines have an estimated average maximum residence time ranging from 6 to 15 yr and an estimated average minimum residence time ranging from 3.6 to 8.9 yr. It was estimated that, on average, 10(10) kJ degrees C-1 of heat energy could be extracted from the mines. Overall, this study has shown that abandoned underground mines contain enough stored heat to be used as thermal resources for ground source heat pump systems, and that the number and extent of mines within Ohio could make this type of geothermal resource valuable.

The GRACE gravity and subglacial terrain data of Wilkes Land are consistent with the presence of a mascon produced by giant impact perhaps at the end of the Permian. In contrast to the relatively extensive ice probing radar coverage, aeromagnetic data coverage is limited across the basin. However, Magsat, Ørsted, and CHAMP satellite magnetic observations reveal the thinned crust of the impact site to be associated with the largest satellite altitude crustal magnetic anomaly of Antarctica. The underlying region of enhanced magnetization is consistent with the GRACE gravity and BEDMAP terrain data and extends into south-central Australia in a reconstructed Gondwana. The strongly magnetized crust can reflect the impact's thermal enhancement of lower crustal viscous remanent magnetization as well as the production of positively magnetized melt rocks within the fractured crust.

New details on the east Antarctic gravity field from the Gravity Recovery and Climate Experiment (GRACE) mission reveal a prominent positive free‐air gravity anomaly over a roughly 500‐km diameter subglacial basin centered on (70°S, 120°E) in north central Wilkes Land. This regional inverse correlation between topography and gravity is quantitatively consistent with thinned crust from a giant meteorite impact underlain by an isostatically disturbed mantle plug. The inferred impact crater is nearly three times the size of the Chicxulub crater and presumably formed before the Cretaceous formation of the east Antarctic coast that cuts the projected ring faults. It extensively thinned and disrupted the Wilkes Land crust where the Kerguelen hot spot and Gondwana rifting developed but left the adjacent Australian block relatively undisturbed. The micrometeorite and fossil evidence suggests that the impact may have occurred at the beginning of the greatest extinction of life on Earth at ∼260 Ma when the Siberian Traps were effectively antipodal to it. Antipodal volcanism is common to large impact craters of the Moon and Mars and may also account for the antipodal relationships of essentially half of the Earth's large igneous provinces and hot spots. Thus, the impact may have triggered the “Great Dying” at the end of the Permian and contributed to the development of the hot spot that produced the Siberian Traps and now may underlie Iceland. The glacial ice up to a few kilometers thick that has covered the crater for the past 30–40 Ma poses formidable difficulties to sampling the subglacial geology. Thus, the most expedient and viable test of the prospective crater is to survey it for relevant airborne gravity and magnetic anomalies.

Regional spherical coordinate observations of the Earth's crustal magnetic field components are becoming increasingly available from shipborne, airborne, and satellite surveys. In assessing the geological significance of these data, theoretical anomalous magnetic fields from geologic models in spherical coordinates need to be evaluated. This study explicitly develops the elegant Gauss-Legendre quadrature formulation for numerically modelling the complete magnetic effects (i.e. potential, vector and tensor gradient fields) of the spherical prism. We also use these results to demonstrate the magnetic effects for the crustal prism and to investigate the crustal magnetic effects at satellite altitudes for a large region of the Middle East centred on Iran.

Many of the outlet glaciers in Greenland overlie deep and narrow trenches cut into the bedrock. It is well known that pronounced topography intensifies the geothermal heat flux in deep valleys and attenuates this flux on mountains. Here we investigate the magnitude of this effect for two subglacial trenches in Greenland. Heat flux variations are estimated for idealized geometries using solutions for plane slopes derived by Lachenbruch (1968). It is found that for channels such as the one under Jakobshavn Isbræ, topographic effects may increase the local geothermal heat flux by as much as 100%.

Analysis of satellite-measured gravity and topography can provide crust-to-core mass variation models for new insi@t on the geologic evolution of the Earth. The internal structure of the Earth is mostly constrained by seismic observations and geochemical considerations. We suggest that these constraints may be augmented by gravity drilling that interprets satellite altitude free-air gravity observations for boundary undulations of the internal density layers related to mass flow. The approach involves separating the free-air anomalies into terrain-correlated and -decorrelated components based on the correlation spectrum between the anomalies and the gravity effects of the terrain. The terrain-decorrelated gravity anomalies are largely devoid of the long wavelength interfering effects of the terrain gravity and thus provide enhanced constraints for modeling mass variations of the mantle and core. For the Earth, subcrustal interpretations of the terrain-decorrelated anomalies are constrained by radially stratified densities inferred from seismic observations. These anomalies, with frequencies that clearly decrease as the density contrasts deepen, facilitate mapping mass flow patterns related to the thermodynamic state and evolution of the Earth's interior.

Satellite magnetometer observations of the Greenland-Iceland region compare quite well with lower altitude data. The satellite magnetic data suggest magnetically enhanced crust was emplaced by the Iceland Plume. Crustal thicknesses, which may be more than 30 km for the Greenland-Scotland Ridge, were obtained from inversion of the compensating terrain gravity effects that were estimated by spectral correlation analysis of the free-air gravity anomalies and terrain gravity effects. Regional magnetic anomaly maxima overlie possible thickened crust from eastern Iceland to the Greenland Coast. The Iceland-Faroe Ridge may involve thinner crust than the Greenland-Iceland portion of the Greenland-Scotland Ridge. The gravity derived crustal model exceeds a 0.7 correlation with available seismic estimates. In thermally active areas our gravity Moho estimates are systematically deeper than the seismic estimates suggesting local density reductions of the underlying lower crust/upper mantle. In south central Greenland, on the other hand, the gravity Moho estimates are shallower than seismic estimates to suggest a local enhancement of the lower crust/upper mantle density. The dichotomous crust of the Greenland-Iceland and Iceland-Faroe Ridges suggests unequal crustal development by the Iceland Plume and the Mid-Atlantic Ridge, where more crustal material may have been contributed to the North Atlantic Plate than the Eurasian Plate. A new thermal modeling scheme based on Poisson's relation between point pole gravity and thermal potentials allows estimation of magnetic crustal thicknesses. Subsequent magnetic anomaly inversion for susceptibility contrasts infers crustal development of the Greenland-Scotland Ridge by temporally variable pulses in plume strength.