Depositional and Hydrological Relationships Between Buried Dead Ice and the Active Layer in the McMurdo Dry Valleys, Antarctica: A Study of Sediment Geochemistry and Cation Concentrations

ABSTRACT

The McMurdo Dry Valleys, the largest ice‐free region in Antarctica, are home to a cold‐desert hydrologic system of glaciers, snowbanks, streams, and lakes. Freshwater is also stored as dead glacial ice, which is poorly constrained in terms of ion concentrations and interactions with both in situ and overlying sediments. Samples of sediments, glacier ice, dead ice, and lake ice were studied from five sites: three in central Taylor Valley (near Doran, Rhone, and Stocking glaciers), one in Pearse Valley, and one in the Quartermain Mountains (Kennar Valley). Sites were chosen to encompass both warmer, wetter lowland and colder, drier upland regions. X‐ray fluorescence (XRF) analysis was conducted on 38 sediments, and inductively coupled plasma optical emission spectroscopy (ICP‐OES) analysis was conducted on 156 ice samples and 60 sediment leachates. The analyses were designed to geochemically compare active layer sediments and sediments within dead‐ice permafrost. Sediment‐rich dead ice layers contained higher cation concentrations than clean ice layers across all sites. Sediments were likely incorporated via eolian deposition at Doran and glaciofluvial deposition at Rhone, Stocking, and Pearse. Conversely, thin sediment layers in Kennar Valley, the coldest and driest site, were likely incorporated into dead‐ice permafrost via contraction cracks. Surficial sediments and sediments in dead ice were predominantly sourced from local bedrock outcrops and were geochemically similar within a given location, indicating that dead‐ice sediments were incorporated at or near the site rather than farther up on the source glaciers. Both surficial sediments and dead‐ice sediments also yielded chemical index of alteration (CIA) values of 40–50, indicating limited chemical weathering in the active layers at these sites. Hydrological interactions between modern active layers and underlying dead‐ice permafrost appeared to be minimal given that the dead ice had different Ca ²⁺ :K ⁺ :Mg ²⁺ :Na ⁺ ratios than sediment leachates and total cation concentrations were not higher at the dead ice surface than they were at depth.