New Last Glacial Maximum ice thickness constraints for the Weddell Sea Embayment, Antarctica

Abstract

Abstract. We describe new Last Glacial Maximum (LGM) ice thickness constraints for three locations spanning the Weddell Sea Embayment (WSE) of Antarctica. Samples collected from the Shackleton Range, Pensacola Mountains, and the Lassiter Coast constrain the LGM thickness of the Slessor Glacier, Foundation Ice Stream, and grounded ice proximal to the modern Ronne Ice Shelf edge on the Antarctic Peninsula, respectively. Previous attempts to reconstruct LGM-to-present ice thickness changes around the WSE used measurements of long-lived cosmogenic nuclides, primarily 10Be. An absence of post-LGM apparent exposure ages at many sites led to LGM thickness reconstructions that were spatially highly variable and inconsistent with flow line modelling. Estimates for the contribution of the ice sheet occupying the WSE at the LGM to global sea level since deglaciation vary by an order of magnitude, from 1.4 to 14.1 m of sea level equivalent. Here we use a short-lived cosmogenic nuclide, in situ-produced 14C, which is less susceptible to inheritance problems than 10Be and other long-lived nuclides. We use in situ 14C to evaluate the possibility that sites with no post-LGM exposure ages are biased by cosmogenic nuclide inheritance due to surface preservation by cold-based ice and non-deposition of LGM-aged drift. Our measurements show that the Slessor Glacier was between 310 and up to 655 m thicker than present at the LGM. The Foundation Ice Stream was at least 800 m thicker, and ice on the Lassiter Coast was at least 385 m thicker than present at the LGM. With evidence for LGM thickening at all of our study sites, our in situ 14C measurements indicate that the long-lived nuclide measurements of previous studies were influenced by cosmogenic nuclide inheritance. Our inferred LGM configuration, which is primarily based on minimum ice thickness constraints and thus does not constrain an upper limit, indicates a relatively modest contribution to sea level rise since the LGM of < 4.6 m, and possibly as little as < 1.5 m.

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

“…However, further evidence for an Antarctic contribution to MWP‐1a from data on land and the continental margin in other regions such as the Weddell Sea (Arndt et al, 2017; Nichols et al, 2019) is absent, and this issue remains a conundrum (Goehring et al, 2019; Hall et al, 2015; Prothro et al, 2020). The large uncertainties in the underpinning sea level constraints (Hibbert et al, 2016, 2018; Stanford et al, 2011) and dating of geological material on land and in the ocean (e.g., see discussion of cosmogenic dating in Siegert et al, 2019, and radiocarbon dating in Anderson et al, 2014), and the uncertainty around the AIS size, seaward extent, thickness and volume above flotation at the LGM, mean that currently it remains difficult to quantify the exact contribution of AIS melting to the sea level rise recorded during MWP‐1a.…”

Cosmogenic nuclide exposure age scatter records glacial history and processes in McMurdo Sound, Antarctica

“…Quartz separates were purified by leaching in a HNO 3 /HF acid solution, and then 10 Be qtz was extracted from purified quartz, both according to standard protocols in the Cosmogenic Nuclide Dating Group and established methods (Brown et al, 1991;Kohl and Nishiizumi, 1992). 10 Be/ 9 Be ratios were measured at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory and normalized to 07KNSTD3110, which has an assumed 10 Be/ 9 Be ratio of 2.85 × 10 −12 (Nishiizumi et al, 2007). 10 Be qtz exposure ages were calculated using Version 3 of the online exposure age calculator hosted by the University of Washington (https://hess.ess.washington.edu/) (Balco et al, 2008) assuming a rock density of 2.7 g cm −3 corrected for shielding and thickness, the Antarctica-specific atmospheric model (ANT) (Stone, 2000), the global 10 Be production rate (4.15 atoms g −1 yr −1 ) (Martin et al, 2017), and the LSDn scaling scheme (Lifton et al, 2014) for the same reasons explained for 3 He pyx above.…”

“…The problem of inherited nuclides and exposure age scatter is exacerbated in Antarctica, where large polythermal ice sheets, hyper-arid polar desert climate conditions, and extremely low sub-aerial erosion rates have persisted since the Miocene (Lamp et al, 2017;Lewis and Ashworth, 2016;Lewis et al, 2008;Shakun et al, 2018;Sugden and Denton, 2004;Sugden et al, 2006). Glacial sediments in ice-free areas of Antarctica preserve direct geological constraints on former ice sheet configurations from Holocene to Miocene times (Anderson et al, 2020;Balco et al, 2013;Balter-Kennedy et al, 2020;Bromley et al, 2010;Christ and Bierman, 2020;Hall et al, 2015;Jones et al, 2015Jones et al, , 2021Nichols et al, 2019;Spector et al, 2017). Cosmogenic nuclides are often the only method available for constraining a numerical chronology of Antarctic glacial deposits.…”

Comparing Glacial‐Geological Evidence and Model Simulations of Ice Sheet Change since the Last Glacial Period in the Amundsen Sea Sector of Antarctica

“…These were deduced using methods such as radiocarbon dating of marine sediments, bathymetric and seismic surveys of submarine glacial bedforms, and cosmogenic nuclide surface exposure dating of terrestrial rock outcrops near modern ice margins. A number of subsequent studies have further improved our knowledge of last deglacial ice sheet surface elevation changes across the continent (e.g., Antarctic Peninsula: Glasser et al., 2014; Jeong et al., 2018; Amundsen‐Bellingshausen sector: Johnson et al., 2017; Johnson et al., 2020; Ross Sea sector: Balco et al., 2019; Goehring et al., 2019; Jones et al., 2015; Smellie et al., 2017; Spector et al., 2017, 2019; Yokoyama et al., 2016 and others; East Antarctica: Jones et al., 2017; Strub et al., 2015; Weddell Sea sector: Bentley et al., 2017; Balco et al., 2017; Nichols et al., 2019 and references therein). Marine geological data show that grounding line retreat from the outer continental shelf largely occurred prior to the Holocene, between approximately 20 and 10 ka, driven primarily by rising global sea‐levels associated with Northern Hemispheric deglaciation.…”