Brief communication: New radar constraints support presence of ice older than 1.5 Myr at Little Dome C

Abstract

Abstract. The area near Dome C, East Antarctica, is thought to be one of the most promising targets for recovering a continuous ice-core record spanning more than a million years. The European Beyond EPICA consortium has selected Little Dome C (LDC), an area ∼ 35 km southeast of Concordia Station, to attempt to recover such a record. Here, we present the results of the final ice-penetrating radar survey used to refine the exact drill site. These data were acquired during the 2019–2020 austral summer using a new, multi-channel high-resolution very high frequency (VHF) radar operating in the frequency range of 170–230 MHz. This new instrument is able to detect reflectors in the near-basal region, where previous surveys were largely unable to detect horizons. The radar stratigraphy is used to transfer the timescale of the EPICA Dome C ice core (EDC) to the area of Little Dome C, using radar isochrones dating back past 600 ka. We use these data to derive the expected depth–age relationship through the ice column at the now-chosen drill site, termed BELDC (Beyond EPICA LDC). These new data indicate that the ice at BELDC is considerably older than that at EDC at the same depth and that there is about 375 m of ice older than 600 kyr at BELDC. Stratigraphy is well preserved to 2565 m, ∼ 93 % of the ice thickness, below which there is a basal unit with unknown properties. An ice-flow model tuned to the isochrones suggests ages likely reach 1.5 Myr near 2500 m, ∼ 65 m above the basal unit and ∼ 265 m above the bed, with sufficient resolution (19 ± 2 kyr m−1) to resolve 41 kyr glacial cycles.

High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years

“…Even though such vertically long antennae would have difficulty in mounting on ground-based platforms, they provide an important opportunity for improving conventional radar systems. Modern radar sounders with phase analysis and SAR processing (e.g., Rodriguez-Morales et al, 2020;Lilien et al, 2021) are able to remove hyperbolic effects. For improving the accuracy of bedrock topography measurements, we can apply radar with high-gain and high-directivity antennae, state-of-the-art modern radar with focused SAR processing, or both.…”

“…Ice radar observations have been conducted in the vicinity of the domes in the EAIS, such as Dome A (e.g., Sun et al, 2009;Bell et al, 2011), Dome C (e.g., Young et al, 2017;Lilien et al, 2021), and Titan Dome (Beem et al, 2021), which numerical modelling studies have identified as candidate areas for future deep drilling. In the Dome Fuji region, a candidate area for deep drilling, after ground-based radar surveys were conducted by the JARE from the late 1980s until 2013, an extensive airborne radar survey was carried out over a 20000 km 2 area during the 2014-2015 and 2016-2017 austral summers (Karlsson et al, 2018) (Fig.…”

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

“…The LDC area was first highlighted as a key Beyond EPICA -Oldest Ice target site in the Van Liefferinge and study. The ice core drilling site has since then been narrowed down to a precise location on LDC through successive radar survey collections (Young et al, 2017;Lilien et al, 2021) and modeling efforts (Parrenin et al, 2017;Cavitte et al, 2018;Van Liefferinge et al, 2018;Passalacqua et al, 2018), in preparation for drilling (Fig. 1).…”

“…Depth uncertainties are also assigned to the undated IRHs (Table 4). Since these IRHs do not reach the MCM/JKB1a/EDMC01a transect, their depths are measured at the closest point along the DELORES radar transect HRB7-HRB8 to the final chosen BE-OI drill site BELDC (75.29917 • S, 122.44516 • E) (Lilien et al, 2021), and their uncertainties are constrained as described above but with their range precision defined by their SNR along this DE-LORES transect. We assume that the firn correction and error calculated at the EDC site are also applicable to this site over LDC.…”

Comment on tc-2021-266

“…Ice radar observations have been conducted in the vicinity of the domes in the EAIS, such as Dome A (e.g., Sun et al, 2009;Bell et al, 2011), Dome C (e.g., Young et al, 2017;Lilien et al, 2021), and Titan Dome (Beem et al, 2021), which numerical modelling studies have identified as candidate areas for future deep drilling. In the Dome Fuji region, a candidate area for deep drilling, after ground-based radar surveys were conducted by the JARE from the late 1980s until 2013, an extensive airborne radar survey was carried out over a 20000 km 2 area during the 2014-2015 and 2016-2017 austral summers (Karlsson et al, 2018) (Fig.…”