Search for: All records

Abstract The landscape hidden beneath the Greenland Ice Sheet remains one of the most sparsely mapped regions on Earth, but offers a unique record of environmental conditions prior to and during widespread glaciation, and of the ice sheet's response to changing climates. In particular, subglacial valleys observed across Greenland may preserve geomorphological information pertaining to landscape and ice sheet evolution. Here we analyze the morphology of a subglacial valley network in northern Greenland using bed elevation measurements acquired during multi‐year airborne radio‐echo sounding surveys. Channel profile morphologies are consistent with a primarily fluvial origin of the network, with evidence for localized modification by ice and/or meltwater. Gravity and magnetic anomalies suggest that the spatial organisation of the valley network is influenced by regional‐scale geological structure, implying a long‐lived and well‐established hydrological system. We also document two knickzones in the valley longitudinal profile and terraces above the channel floor in the lower course of the network. These observations, combined with stream power modeling, indicate that northern Greenland experienced two episodes of relative base level fall during the Neogene (∼150 m at ca. 12–3.7 Ma and ∼380 m at ca. 8.2–2.8 Ma) that resulted in channel profile adjustment via incision and knickzone retreat. The timing of the inferred base level fall correlates with other onshore and offshore records of uplift, denudation, and/or relative sea level change, and we suggest that tectonic and/or mantle‐driven uplift played an important role in the genesis of the modern landscape of northern Greenland. 

Abstract 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. 

Abstract From 2015 to 2017, theROSETTA‐Ice project comprehensively mapped Antarctica's Ross Ice Shelf using IcePod, a newly developed aerogeophysical platform. The campaign imaged the ice‐shelf surface with lidar and its internal structure with ice‐penetrating radar. TheROSETTA‐Ice data was combined with pre‐existing ice surface and bed topography digital elevation models to create the first augmented reality (AR) visualisation of the Antarctic Ice Sheet, using the Microsoft HoloLens. TheROSETTA‐Ice datasets support cross‐disciplinary science that aims to understand 4D processes, namely the change of 3D ice‐shelf structures over time. The work presented here usesARto visualise this dataset in 3D and highlights howARcan be simultaneously a useful research tool for interdisciplinary geoscience as well as an effective device for science communication education. 

Abstract Basal melting of ice shelves is a major source of mass loss from the Antarctic Ice Sheet. In situ measurements of ice shelf basal melt rates are sparse, while the more extensive estimates from satellite altimetry require precise information about firn density and characteristics of near‐surface layers. We describe a novel method for estimating multidecadal basal melt rates using airborne ice penetrating radar data acquired during a 3‐year survey of the Ross Ice Shelf. These data revealed an ice column with distinct upper and lower units whose thicknesses change as ice flows from the grounding line toward the ice front. We interpret the lower unit as continental meteoric ice that has flowed across the grounding line and the upper unit as ice formed from snowfall onto the relatively flat ice shelf. We used the ice thickness difference and strain‐induced thickness change of the lower unit between the survey lines, combined with ice velocities, to derive basal melt rates averaged over one to six decades. Our results are similar to satellite laser altimetry estimates for the period 2003–2009, suggesting that the Ross Ice Shelf melt rates have been fairly stable for several decades. We identify five sites of elevated basal melt rates, in the range 0.5–2 m a⁻¹, near the ice shelf front. These hot spots indicate pathways into the sub‐ice‐shelf ocean cavity for warm seawater, likely a combination of summer‐warmed Antarctic Surface Water and modified Circumpolar Deep Water, and are potential areas of ice shelf weakening if the ocean warms.