The geochemical and mineralogical fingerprint of West Antarctica's weak underbelly: Pine Island and Thwaites glaciers

Abstract

The marine-based West Antarctic Ice Sheet (WAIS) is considered the most unstable part of the Antarctic Ice Sheet, with particular vulnerability in the Amundsen Sea sector where glaciers are melting at an alarming rate. Far-field sea-level data and ice-sheet models have pointed towards at least one major WAIS disintegration during the Late Quaternary, but direct evidence for past collapse(s) from ice-proximal geological archives remains elusive. In order to facilitate geochemical and mineralogical tracing of the two most important glaciers draining into the Amundsen Sea, i.e. Pine Island Glacier (PIG) and Thwaites Glacier (TG), we here provide the first multi-proxy provenance analysis of 26 seafloor surface sediment samples from Pine Island Bay.Our data show that the fingerprints of detritus delivered by PIG and TG are clearly distinct near the ice-shelf fronts of both ice-stream systems for all grain sizes and proxies investigated. Glacial detritus delivered by PIG is characterised by low εNd values (~-9), high 87 Sr/ 86 Sr ratios (~0.728), low smectite content (<10%), and hornblende and biotite grains with Late Permian to Jurassic (170-270 Ma) cooling ages. In contrast, glacigenic detritus delivered by TG is characterised by higher εNd values (~-4), lower 87 Sr/ 86 Sr ratios (0.714), higher smectite (20%) and kaolinite content (37%), biotite and hornblende grains with 40 Ar/ 39 Ar cooling ages of <40 Ma and ~115 Ma, and high content of mafic minerals.The geochemical and mineralogical fingerprints for PIG and TG reported here provide novel insights into sub-ice geology and allow us to trace both drainage systems in the geological past, under environmental conditions more similar to those envisioned in the next 50 to 100 years.

Ocean‐Forced Instability of the West Antarctic Ice Sheet Since the Mid‐Pleistocene

“…Overall, the detrital continental margin sediments reflecting the PSAs of West Antarctica (circles in Figure 6b) have ε Nd values ranging from −11.9 to +1.3 and 87 Sr/ 86 Sr ratios ranging from 0.705 to 0.750 (Simões Pereira et al., 2018, 2020). Note that there is also heterogeneity between samples collected from different locations within a given coastal region.…”

“…For example, detrital sediments in the Eastern Amundsen Sea (EAS) have a range of 87 Sr/ 86 Sr ratios from 0.710 to 0.727, with ε Nd values between −8.3 and −3.4, while detrital sediments in the Western Amundsen Sea (WAS) have a narrower range of 87 Sr/ 86 Sr ratios from 0.708 to 0.710, with ε Nd values between −2.9 and −1.7 (Figure 6b). These differences reflect the different sediment sources to the WAS and EAS, with detritus in the WAS sourced from Mesozoic coastal granites, while bedrock or sediment‐fill beneath the Pine Island Glacier and Thwaites Glacier are the main sources of sediment to the EAS (Simões Pereira et al., 2018, 2020). The Sr‐Nd isotope signatures in the EAS (Figure 6b) are also sensitive to contributions from Pine Island Glacier (low ε Nd values, high 87 Sr/ 86 Sr ratios) versus Thwaites Glacier (higher ε Nd values, lower 87 Sr/ 86 Sr ratios; Simões Pereira et al., 2018, 2020).…”

“…These differences reflect the different sediment sources to the WAS and EAS, with detritus in the WAS sourced from Mesozoic coastal granites, while bedrock or sediment‐fill beneath the Pine Island Glacier and Thwaites Glacier are the main sources of sediment to the EAS (Simões Pereira et al., 2018, 2020). The Sr‐Nd isotope signatures in the EAS (Figure 6b) are also sensitive to contributions from Pine Island Glacier (low ε Nd values, high 87 Sr/ 86 Sr ratios) versus Thwaites Glacier (higher ε Nd values, lower 87 Sr/ 86 Sr ratios; Simões Pereira et al., 2018, 2020). For the Ross Sea, decarbonated sediment in the Eastern Ross Sea (ERS) yields 87 Sr/ 86 Sr ratios of 0.715–0.717, with ε Nd values between −6.6 and −5.8, while the WRS and the central Ross Sea are characterized by 87 Sr/ 86 Sr ratios of 0.712–0.715 and 0.717 to 0.725, with ε Nd values ranging from −5.4 to −4.6 and −11.9 to −7.3, respectively (Figure 6b; Farmer et al., 2006).…”

“…Endmember data for clay minerals are from previous studies (Diekmann et al., 2004; Ehrmann et al., 2005, 2011; Hillenbrand, 2000, 2001; Hillenbrand et al., 2003; Jung et al., 2021; Pant et al., 2013; Setti et al., 2004). Sr‐Nd isotope data are from previous studies (Adams et al., 2005; Blakowski et al., 2016; Farmer et al., 2006; Futa & Le Masurier, 1983; Hart et al., 1997; Korhonen et al., 2010; McCarron & Smellie, 1998; Pankhurst et al., 1993; Riley et al., 2001; Ryan, 2007; Simões Pereira et al., 2018, 2020). Abbreviations: AI, Alexander Island; CRP‐1, Cape Roberts Project‐1; DV, Dry Valleys; EAS, Eastern Amundsen Sea; ERS, Eastern Ross Sea; GL, Graham Land; MBL, Marie Byrd Land; MS, McMurdo Sound; NVL, North Victoria Land; PIG, Pine Island Glacier; PL, Palmer Land; RHC, Ruppert and Hobbs Coasts; TG, Thwaites Glacier; TI, Thurston Island; WAP, West Antarctic Peninsula; WAS, Western Amundsen Sea; WRS, Western Ross Sea.…”

Quantitative Sub-Ice and Marine Tracing of Antarctic Sediment Provenance (TASP v0.1)

“…Cenozoic volcanics are extended, largely under Thwaites Glacier, using interpretations of magnetic, gravimetric, and topographic data (Jordan et al, 330 2020b) as well as airborne radar data that indicate enhanced subglacial melting due to elevated geothermal heat flux (Schroeder et al, 2014). Mafic rocks are assumed to include gabbros of Cenozoic age (Simões Pereira et al, 2020), similar to Dorrell Rock near Mt. Murphy.…”