Abstract. The distribution of moraines in the Transantarctic Mountains affords direct constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). Here, we describe glacial geologic observations and cosmogenic-nuclide exposure ages from Roberts Massif, an ice-free area in the central Transantarctic Mountains. We measured cosmogenic 3He, 10Be, 21Ne, and 26Al in 168 dolerite and sandstone boulders collected from 24 distinct deposits. Our data show that a cold-based EAIS was present, in a configuration similar to today, for many periods over the last ∼14.5 Myr, including the mid-Miocene, late Pliocene, and early to Middle Pleistocene. Moraine ages at Roberts Massif increase with distance from, and elevation above, the modern ice margin, which is consistent with a persistent EAIS extent during glacial maxima and slow, isostatic uplift of the massif itself in response to trough incision by outlet glaciers. We also employ the exceptionally high cosmogenic-nuclide concentrations in several boulders, along with multi-isotope measurements in sandstone boulders, to infer extremely low erosion rates (≪5 cm Myr−1) over the period covered by our record. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and similar to its current configuration during at least some periods when the global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.
The Younger Dryas (YD: 12.9-11.7 ka) is a canonical example of abrupt climate change and has evolved in interpretation from a cold snap of possibly global extent to a primarily Northern Hemisphere event centered on the North Atlantic and linked to meltwater-forced disturbance of Atlantic meridional overturning circulation (AMOC) (Broecker et al., 2010;McManus et al., 2004). Northern Hemisphere palaeoclimate data confirm the YD was accompanied by atmospheric circulation shifts (Mayewski et al., 1994), permafrost expansion (Isarin, 1997), and disruption of the Asian monsoon (Cheng et al., 2020;Liu et al., 2008), while ice cores document the rapidity of these shifts (<10 years; Alley, 2000;Steffensen et al., 2008). Nonetheless, a satisfactory trigger for the YD is elusive, partly because our understanding of the event's manifestation continues to evolve (Cheng et al., 2020). For instance, emerging data suggest an out-of-phase relationship between glacier records and traditional interpretations of Lateglacial climate proxies in Europe and the circum North Atlantic (Foreman et al., 2022;Wittmeier et al., 2020). Noting the apparent disparity between the 16°C cooling inferred from Greenland δ 18 O and the muted advances of local glaciers, Denton et al. (2005) hypothesized that YD cooling was greater in winter than summer, reflecting the impact of expanded winter sea ice on ocean-atmosphere heat transfer. Recent glacial studies have explored this model further, suggesting that North Atlantic YD summers did not cool or may even have been anomalously warm (
Erosion beneath glaciers and ice sheets is a fundamental Earth-surface process dictating landscape development, which in turn influences ice-flow dynamics and the climate sensitivity of ice masses. The rate at which subglacial erosion takes place, however, is notoriously difficult to observe because it occurs beneath modern glaciers in a largely inaccessible environment. Here, we present 1) cosmogenic-nuclide measurements from bedrock surfaces with well constrained exposure and burial histories fronting Jakobshavn Isbræ in western Greenland to constrain centennial-scale erosion rates, and 2) a new method combining cosmogenic nuclide measurements in a shallow bedrock core with cosmogenic-nuclide modelling to constrain orbital-scale erosion rates across the same landscape. Twenty-six 10Be measurements in surficial bedrock constrain the erosion rate during historical times to 0.4–0.8 mm yr-1. Seventeen 10Be measurements in a 4-m-long bedrock core corroborate this centennial-scale erosion rate, and reveal that 10Be concentrations below ~2 m depth are greater than what is predicted by an idealized production-rate depth profile. We utilize this excess 10Be at depth to constrain orbital-scale erosion rates at Jakobshavn Isbræ to 0.1–0.3 mm yr-1. The broad similarity between centennial- and orbital-scale erosion rates suggests that subglacial erosion rates have remained relatively uniform throughout the Pleistocene at Jakobshavn Isbræ.
<p>The Juneau Icefield Research Program (JIRP) has provided Polar science and research experiences for undergraduates for 75 years, positioning itself as an important pipeline to careers in the Polar sciences and the geosciences at large. With the goal of increasing diversity within the Polar science pipeline and increasing awareness of Polar science career paths, JIRP is partnering with federally funded Upward Bound programs around the United States to offer a two-week, cost-free Polar science experience modeled after JIRP for highschool students from low income families where neither parent holds a bachelor&#8217;s degree. As a precursor to the JIRB-UB experience, we prepared a two week virtual course for Upward Bound students from Washington State University that could easily be adapted to a higher education environment. The goals of our course were: 1) inspiring excitement for and participation in the JIRP-UB program; 2) creating awareness about Polar science career paths; and 3) developing a foundational understanding of Polar science concepts. We covered an orientation to JIRP and the basics of glacier and climate science, including glacier mass balance. We framed the curriculum around a scientific expedition, where students first created an expedition plan during Week 1, and then analyzed mass balance and climate data that was &#8220;collected&#8221; on their expedition during Week 2. Specifically, we used publicly available data to help students re-create a figure from a recently published paper using Google Sheets. The curriculum was designed so that students could opt to take either one or both weeks of the course. This curriculum could also serve as an introduction to glacier science in a higher education setting, offering students a virtual field experience. As the geosciences community grapples with a severe lack of diversity, our goal is to use this expedition-style curriculum to broaden participation and engagement in the Polar sciences and beyond.&#160;</p>
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