Search

The retrieval of continuous ice core records of more than 1 Myr is an important challenge in palaeo-climatology. For identifying suitable sites for drilling such ice, knowledge of the subglacial topography and englacial layering is crucial. For this purpose, extensive ground-based ice radar surveys were carried out over Dome Fuji in the East Antarctic plateau during the 2017/18 and 2018/19 austral summers by the Japanese Antarctic Research Expedition, on the basis of ground-based radar surveys conducted over the previous ∼ 30 years. High-gain Yagi antennae were used to improve the antenna beam directivity, thereby significantly decreasing hyperbolic features of unfocused along-track diffraction hyperbolae in the echoes from mountainous ice–bedrock interfaces. We combined the new ice thickness data with the previous ground-based data, recorded since the 1980s, to generate an accurate high-spatial-resolution (up to 0.5 km between survey lines) ice thickness map. This map revealed a complex landscape composed of networks of subglacial valleys and highlands. Based on the new map, we examined the roughness of the ice–bed interface, the bed surface slope, the driving stress of ice and the subglacial hydrological condition. These new products and analyses set substantial constraints on identifying possible locations for new drilling. In addition, our map was compared with a few bed maps compiled by earlier independent efforts based on airborne radar data to examine the difference in features between datasets. Our analysis suggests that widely available bed topography products should be validated with in situ observations where possible. [ABSTRACT FROM AUTHOR]

• A data set of 10Be in surface snow from coastal to inland Antarctica is presented. • A boundary of the deposition regime was found at around 75°S at 3.5 km elevation. • Transport from the stratosphere might also affect the spatial distribution of 10Be. To contribute further to understanding of the nature of 10Be deposition in Antarctica, we determined 10Be concentrations in surface snow samples obtained along the inland traverse route of the 59th and 60th Japanese Antarctic Research Expeditions (JAREs) in eastern Dronning Maud Land. The 10Be concentrations ranged between 3.7 × 103 and 8.6 × 104 atoms/g. When plotted against latitude, they showed a clear trend of increasing concentration southward with an upward inflection point at around 75°S (elevation 3.5 km) for the 59th JARE. Comparison with both snow accumulation rate and δ18O data suggests that the inflection point divides the dominant deposition regime into two different groups: wet deposition (north of 75°S) and dry deposition with slight enhancement of 10Be fallout further inland (south of 75°S). Additional factors associated with 10Be transport from the stratosphere are also proposed. [ABSTRACT FROM AUTHOR]

The recovery of a new Antarctic ice core to cover one million years will advance our understandings of the Quaternary climate. Previous studies have indicated that such old ice may exist in inland areas of the Antarctic continent, where the ice is thick enough (but not too thick), accumulation rate is low, basal temperature is well below the pressure melting point, and horizontal ice flow is slow (Pattyn 2010; Fischer et al. 2013; Van Liefferinge and Pattyn 2013; Sun et al. 2014; Parrenin et al. 2017). In the efforts to select the drilling site in the Dome Fuji area, the 59th Japanese Antarctic Research Expedition (JARE 59, 2017-2018 Antarctic summer) conducted intense glaciological field surveys. In particular, a densely arranged ground-based radar survey improved the mapping of bedrock topography as well as internal layers of the ice sheet around Dome Fuji. Three shallow ice cores (40 - 152 m depth) were also drilled for better constraining the spatial differences of accumulation rate in the area. We have been analyzing the new and existing field data, and conducting ice flow modelings constrained by the data, to estimate the flow and age of ice near the bed of the ice sheet, as the essential parts of the site selection activities.As the first step of modelings to aid interpretation of the field data, we use an one-dimensional ice flow model to simulate the vertical profile of temperature and age of ice. The modeled age and temperature profiles at the previous Dome Fuji drilling site are first compared with the depth-age relationship of the Dome Fuji deep ice core (3034 m, 720 kyr) and borehole temperature to optimize model parameters such as geothermal heat flux and vertical-strain-rate parameterization. The model is then applied to the vicinity of Dome Fuji along the transect of JARE 59 surveys, and simulated age profiles are compared with internal layers of the ice sheet, to estimate the areas where very old ice may exist or where the ice bed is melting. We also investigate the influence of various glaciological parameters such as ice thickness, accumulation rate, geothermal heat flux, and thinning rate, on the age estimation of ice especially in the lowest few hundred meters. In the presentation, we will discuss potential sites around Dome Fuji and the relative importance of uncertain glaciological parameters on the age estimation of the deepest layers in the ice sheet. Our results were also partly used for the planning of survey areas of the Japan-Norway-US international survey with JARE 60 using higher-performance ice radars (see presentation by Shuji Fujita et al. in the same session). [ABSTRACT FROM AUTHOR]