Radar‐Detected Englacial Debris in the West Antarctic Ice Sheet

Abstract

Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transportation and deposition downstream. Sediments potentially rich in essential nutrients, like silica and iron, can thus be transferred from continental sources to the ocean, where deposition could enhance marine primary productivity. However, a lack of data has limited our knowledge of sediment entrainment, transfer, and distribution in Antarctica, until now. We use ice‐penetrating radar to examine englacial sediments in the Weddell Sea sector of the West Antarctic Ice Sheet. Radargrams reveal englacial reflectors on the leeside of nunataks and subglacial highlands, where Mie scattering analysis of the reflectors suggests particle sizes consistent with surface moraine sediments. We hypothesize that these sediments are entrained at the thermal boundary between cold and warm‐based ice. Conservative estimates of >130 × 109 kg of englacial sediment in Horseshoe Valley alone suggest that the ice sheet has significant entrainment potential unappreciated previously.

Five decades of radioglaciology

“…For example, imprints of shear margin migration or change in flow direction are typically identified based on the amount of stratigraphic disruption. Examples include studies showing changes in ice-flow structure or folded stratigraphy in Greenland and entrained debris in a glacier in Patriot Hills, West Antarctica (Catania and others, 2006; Martín and others, 2009; Dahl-Jensen and others, 2013; Bell and others, 2014; Bingham and others, 2015; Kingslake and others, 2016; Winter and others, 2019; Ross and Siegert, 2020). Advances in processing radargrams to extract ice-sheet structure make it possible to interpret these features in regions of complex flow (Elsworth and others, 2020).…”

Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export

“…While Fe concentrations within terrestrial ice cores and marine ice (formed at the base of some ice shelves) overlap with the TdFe range we report for icebergs herein 53 , critical differences in the distribution of TdFe within recently-calved icebergs may still occur between catchments. This may especially be the case for ice calved from large ice shelves compared to ice calved from inshore marine-terminating glaciers, as the pathways for sediment incorporation into ice (and thus sediment loss from ice) differ between these scenarios and are not well characterized 53,54 . Critical unresolved questions are: how thick are Fe-rich layers, where are they located within different icebergs, how fast are these layers eroded in the marine environment, and how does this vary regionally?…”

Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years

“…Another interesting englacial feature across BIR is an apparent basal layer (Siegert et al, 2013; Figure 6), which looks remarkably similar in appearance to the sediment inclusion observed in Horseshoe Valley (Winter et al, 2019). It can be traced across the entire BIR along a former flow band (i.e., flow stripes).…”

“…Further englacial reflectors may result from basal sediment inclusion (Siegert et al, 2013;Winter et al, 2019) and from where ice is, or has been, floating to form basal crevasses (Kingslake et al, 2018;Wearing & Kingslake, 2019). In all cases, interpreting past flow from internal layers requires consideration of how changes in time may affect layer arrangements.…”

“…Winter et al () analyzed the internal layers within the Independence, Ellsworth, and Horseshoe Valley troughs, concluding that while the pattern of continuous versus disrupted layers is consistent with modern ice flow, supporting little ice flow direction change, evidence exists for former enhanced flow in these tributaries. Horseshoe Valley also contains basal ice structures associated with subglacial hills and pinnacles that are best explained as inclusions of basal sediment (Siegert et al, ; Winter et al, ). The feature can be tracked downstream to the trunk of IIS, but no internal layers exist within it, preventing further tracking (Figure ).…”