The basement depth in the Rio Grande Rise (RGR), South Atlantic, is estimated from combining gravity data obtained from satellite altimetry, marine surveys, bathymetry, sediment thickness and crustal thickness information. We formulate a crustal model of the region by inverse gravity modeling. The effect of the sediment layer is evaluated using the global sediment thickness model of National Oceanic and Atmospheric Administration (NOAA) and fitting the sediment compaction model to observed density values from Deep Sea Drilling Project (DSDP) reports. The Global Relief Model ETOPO1 and constraining data from seismic interpretation on crustal thickness are integrated in the inversion process. The modeled Moho depth values vary between 6 and 27 km over the area, being thicker under the RGR and also in the direction of São Paulo Plateau. The inversion for the gravity-equivalent basement topography is applied to gravity residual data, which is free from the gravity effect of sediments and from the gravity effect of the estimated Moho interface. We find several short-wavelengths structures not present in the bathymetry data. Our model shows a rift crossing the entire Rio Grande Rise deeper than previously presented in literature, with depths up to 5 km in the East Rio Grande Rise (ERGR) and deeper in the West Rio Grande Rise (WRGR), reaching 6.4 km. An interesting NS structure that goes from 34 S and extends through de São Paulo Ridge may be related to the South Atlantic Opening and could reveal an extinct spreading center.

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George VI Sound is an~600 km-long curvilinear channel on the west coast of the southern Antarctic Peninsula separating Alexander Island from Palmer Land. The Sound is a geologically complex region presently covered by the George VI Ice Shelf. Here we model the bathymetry using aerogravity data. Our model is constrained by water depths from seismic measurements. We present a crustal density model for the region, propose a relocation for a major fault in the Sound, and reveal a dense body,~200 km long, flanking the Palmer Land side. The southern half of the Sound consists of two distinct basins~1,100 m deep, separated by a −650 m-deep ridge. This constricting ridge presents a potential barrier to ocean circulation beneath the ice shelf and may account for observed differences in temperature-salinity (T-S) profiles. Plain Language Summary Knowing the seafloor depth beneath ice shelves is crucial for understanding the interaction between the ocean and the overlying ice, as the shape of the sea floor influences water circulation pathways. We present a new bathymetric model of the seafloor beneath George VI Ice Shelf on the Antarctica Peninsula. The data for our model were collected from airborne surveys, including the ice surface elevation, ice thickness, and gravity field measurements. We first present a new geological model of the Sound and use our improved data coverage to relocate a previously interpreted geological fault. The new bathymetry model shows that in the southern segment of the Sound, an area with shallow bathymetry and deep ice might be acting as a barrier to the water flow. This information can change our understanding of the circulation between the northern and southern segments of the Sound and can be used in models of how this impacts the melt in the base of the ice shelf. High basal melt rates around Antarctica have been interpreted as responses to variations in oceanic temperature and circulation (e.g., Holland et al., 2008; Jacobs et al., 2011). Over George VI Ice Shelf, estimated basal melt rates range from 2.8 m/a (Corr et al., 2002) to 6.0 m/a (Dinniman et al., 2012) with a recent study report-ing~4 m/a over a 23 year period (Adusumilli et al., 2018). Future changes in basal melt depend on changes in ocean temperature as well as subsurface currents, steered by the cavity shape, highlighting the importance of accurate bathymetry data for future predictions (e.g.,