High resolution boundary conditions of an old ice target near Dome C, Antarctica

A high resolution (1 km line spacing) aerogeophysical survey was conducted over a region near the East Antarctic Ice Sheet's Dome C that may hold a 1.5 million year old climate record. New ice thickness data derived from an airborne coherent radar sounder was combined with unpublished data that was unavailable for earlier compilations. We find under the primary candidate region elevated rough topography, near a number of subglacial lakes, but also regions of smoother bed. The high resolution of this ice thickness dataset also allows us to explore the nature of ice thickness uncertainties in the context of radar geometry and processing

The distribution of geothermal flux in West Antarctica

The West Antarctic Ice Sheet (WAIS) contains the equivalent of ∼3.3 m of global sea level rise and is the largest ice sheet on Earth grounded almost entirely below sea level. This is a potentially unstable configuration that makes WAIS prone to rapid collapse during interglacial periods, a condition known as marine instability. One poorly understood but possibly dominant process in past and future collapses of WAIS is its coupling with the underlying West Antarctic Rift System (WARS), a Jurassic through Cenozoic region of intracontinental extension characterized by active volcanism. WARS’ topographic range, complex tectonic history, and volcanism exert a large influence on the distribution of elevated geothermal flux, a critical but poorly constrained ice sheet boundary condition for the collapse-prone marine- based WAIS. Examples of elevated geothermal flux have been observed throughout the West Antarctic Rift System (WARS). Uncertainties remain however on the timing, evolution, and extent of both the WARS and its volcanism. In this dissertation I analyze magnetic anomalies in the context of other aerogeophysical data in central West Antarctic Rift System (WARS) in order to evaluate the distribution of potential hotspots in the region. I identify three different regions with distinct magnetic character and correlate each region to specific stages of tectonic and magmatic activity in WARS. My interpretation supports both the hypothesis that Marie Byrd Land was tectonically and magmatically reactivated multiple times during the Jurassic and Cenozoic and that a hotspot was emplaced there later in the Cenozoic. I also use the approach described by Schroeder et al. (2014a) to investigate the distribution of elevated and possibly transient geothermal flux along Marie Byrd Land and the Siple Coast of West Antarctica. I employ a vast archive of radar sounding datasets in West Antarctica and use coherent phase sensitive radar to constrain the geometry of subglacial water systems (Schroeder et al., 2013). Under constrained conditions, the amplitude of radar returns can be used with a subglacial water routing model to infer basal melt (Schroeder et al., 2014a). This technique is based on the assumption that the brightness of radar reflectors is proportional to the areal coverage by water at the ice-bed interface. The assumption is valid in the case of subglacial distributed canals, which have been proved to be the current sub-glacial water system dominating the Thwaites Glacier catchment in West Antarctica (Schroeder et al., 2013). Once a ground water transportation system has been selected, the technique uses the bed topography and ice surface elevation to calculate the hydraulic head in a region, which gives information on the subglacial water flow direction and the extent of the upstream catchment. Both of these quantities are used to estimate the total water flow in the region. If the amount of water detected from the radar amplitude analysis exceeds the estimates of total water flow, then an additional source of basal melting, such as geothermal flux, needs to be invoked. Comparing the results with previous assessments of water production due to basal friction (Joughin et al., 2009), the amount of water melt produced by geothermal flux can be estimated.Geological Science

High mid-Holocene accumulation rates over West Antarctica inferred from a pervasive ice-penetrating radar reflector [in review]

Modelling the past and future evolution of the West Antarctic Ice Sheet (WAIS) to atmospheric and ocean forcing is challenged by the availability and quality of observed palaeo-boundary conditions. Key potential data for reconstructing past ice-sheet processes on large spatial scales are Internal Reflecting Horizons (IRHs) detected by Radio-Echo Sounding (RES) techniques. When isochronal and dated at ice cores, IRHs can be used to determine palaeo-accumulation rates and patterns. Using a spatially extensive IRH over Pine Island Glacier, Thwaites Glacier, Institute and Möller Ice Streams, and a local layer approximation model, we infer mid-Holocene accumulation rates over the slow-flowing parts of these catchments for the past ~5000 years. By comparing our results with modern climate reanalysis models and observational syntheses, we estimate that accumulation rates over the Amundsen-Weddell-Ross divide were on average 18 % higher than modern rates during the mid-Holocene. However, no significant spatial changes in the accumulation pattern were observed. These higher mid-Holocene accumulation-rate estimates match previous palaeo-accumulation estimates from ice-core and targeted IPR surveys over the ice divide, and also coincide with periods of grounding-line re-advance during the Holocene over the Weddell and Ross Sea sectors. Our results highlight the need for ice-sheet models to account for time-varying accumulation rates across the WAIS during the Holocene to provide better estimates of its contribution to past sea-level rise

A detailed radiostratigraphic data set for the central East Antarctic Plateau spanning from the Holocene to the mid-Pleistocene

We present an ice-penetrating radar data set which consists of 26 internal reflecting horizons (IRHs) that cover the entire Dome C area of the East Antarctic plateau, the most extensive to date in the region. This data set uses radar surveys collected over the space of 10 years, starting with an airborne international collaboration in 2008 to explore the region, up to the detailed ground-based surveys in support of the Beyond EPICA – Oldest Ice (BE-OI) European Consortium. Through direct correlation with the EPICA-DC ice core, we date 19 IRHs that span the past four glacial cycles, from 10 ka, beginning of the Holocene, to over 350 ka, ranging from 10 % to 83 % of the ice thickness at the EPICA-DC ice core site. We indirectly date and provide stratigraphic information for seven older IRHs using a 1D ice flow inverse model, going back to an estimated 700 ka. Depth and age uncertainties are quantified for all IRHs and provided as part of the data set. The IRH data set presented in this study is available at the US Antarctic Program Data Center (USAP-DC) (https://doi.org/10.15784/601411, Cavitte et al., 2020) and represents a contribution to the SCAR AntArchitecture action group (AntArchitecture, 2017)

ADMAP2 Magnetic anomaly map of the Antarctic - links to files

ADMAP2 is the second generation Antarctic magnetic anomaly compilation for the region south of 60°S based on ship- and airborne magnetic anomaly measurements. The distribution comprises a set of full (ADMAP-2) and abridged (ADMAP-2A) databases organised by sub-region and/or survey in Geosoft format, and a set of Geosoft-format grids