A 14.5 million-year record of East Antarctic Ice Sheet fluctuations from the central Transantarctic Mountains, constrained with cosmogenic <sup>3</sup>He, <sup>10</sup>Be, <sup>21</sup>Ne, and <sup>26</sup>Al

Abstract

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 180 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-mid 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 (

Relative terrestrial exposure ages inferred from meteoric <sup>10</sup>Be and NO<sub>3</sub><sup>−</sup> concentrations in soils along the Shackleton Glacier, Antarctica

“…Though our profiles are shallower than profiles from the MDV and Victoria Land in Antarctica (Dickinson et al, 2012;Schiller et al, 2009;Valletta et al, 2015) and Sweden and Alaska in the Arctic (Bierman et al, 2014;Ebert et al, 2012), the soils from these previous studies reached background concentrations of 10 Be within the top 40 cm, which is close to our maximum depth of 30 cm at Thanksgiving Valley. Bennett Platform is most similar to the soil profiles from other regions in Antarctica, as they have decreasing 10 Be concentrations with depth, while The in-situ ages are youngest closer to the glacier at nearly all locations along the Shackleton Glacier (Balter et al, 2020; ICE-D), which is the same trend we observed for the meteoric 10 Be ages. In addition, the in-situ ages and calculated and estimated ages from the Shackleton Glacier region are typically younger at lower elevations and decrease closer to the Ross Ice Shelf (Fig.…”

“…2a) and were either deposited or exposed as the documented a large diamictite that is underlain by soils estimated to be a maximum of >14 Myr in age. While this soil age is likely an overestimate given previously published in-situ ages (Balter et al, 2020), the Sirius Group was not observed near the relatively younger RM2-1 soils, with an inheritance-corrected age of 0.14 Myr. We interpret these sparse data to suggest that either the tills were transported from further inland during previous glacial retreat, or that the Sirius Group formed over an extended period of time.…”

“…rates from rocks of 1 to 65 cm Myr -1 in Victoria Land (Ivy-Ochs et al, 1995;Margerison et al, 2005;Morgan et al, 2010;Strasky et al, 2009;Summerfield et al, 1999) and 5 to cm Myr -1 further south in the Transantarctic Mountains (Ackert and Kurz, 2004;Balter et al, 2020;Morgan et al, 2010). Balter et al (2020) determined that erosion rates for boulders at Roberts Massif which were less than 2 cm Myr -1 . However, we chose a conservative value of 5 cm Myr -1 for the Shackleton Glacier region.…”

Mid-Holocene thinning of David Glacier, Antarctica: Chronology and Controls

“…For 3 He, we targeted pyroxene from the 125-250 micron grain size fraction. Pure pyroxene was obtained using an established HF etching method and 3 He/ 4 He ratios were measured at the Berkeley Geochronology Center noble gas spectrometer following established methods (Bromley et al, 2014;Blard et al, 2015;Balter et al, 2020). We supplemented this data set with eight samples collected prior to the 2016-17 austral summer and those samples were processed with the methods outlined in Oberholzer et al (2003Oberholzer et al ( , 2008Di Nicola et al (2009.…”

Geochemical zones and environmental gradients for soils from the Central Transantarctic Mountains, Antarctica

“…As a result, currently exposed soils were overlain and reworked by fluctuations of the Shackleton Glacier and other tributary and alpine glaciers in the region. Exposure ages range from the early Holocene to the Miocene, and generally increase with distance from the coast and distance from the glacier (Balter et al, 2020;Diaz et al, 2020a).…”