Cryostratigraphy of mid-Miocene permafrost at Friis Hills, McMurdo Dry Valleys of Antarctica

Abstract

The origin and stability of ground ice in the stable uplands of the McMurdo Dry Valleys remains poorly understood, with most studies focusing on the near-surface permafrost. The 2016 Friis Hills Drilling Project retrieved five cores reaching 50 m depth in mid-Miocene permafrost, a period when Antarctica transitioned to a hyper-arid environment. This study characterizes the cryostratigraphy of arguably the oldest permafrost on Earth and assesses 15 Myr of ground ice evolution using the REGO model. Four cryostratigraphic units were identified: 1) surficial dry permafrost (0–30 cm), 2) ice-rich to ice-poor permafrost (0.3–5.0 m) with high solute load and δ18O values (-16.2 ± 1.8‰) and low D-excess values (-65.6 ± 4.3‰), 3) near-dry permafrost (5–20 m) and 4) ice-poor to ice-rich permafrost (20–50 m) containing ice lenses with low solute load and δ18O values (-34.6 ± 1.2‰) and D-excess of 6.9 ± 2.6‰. The near-surface δ18O profile of ground ice is comparable to other sites in the stable uplands, suggesting that this ice is actively responding to changing surface environmental conditions and challenging the assumption that the surface has remained frozen for 13.8 Myr. The deep ice lenses probably originate from the freezing of meteoric water during the mid-Miocene, and their δ18O composition suggests mean annual air temperatures ~7–11°C warmer than today.

Improved prediction of the vertical distribution of ground ice in Arctic-Antarctic permafrost sediments

“…2). In the two deep cores from icy permafrost soils (Beacon Valley and Friis Hills), ice-enrichment is also observed at ~5 m 26,27 . Approximately 70% of the surveyed sites in the stable upland zone (n = 28) have excess ice in the uppermost 2 m below the ice table.…”

“…2) and this led to permafrost being classified mostly as dry permafrost or icecemented permafrost throughout the MDV 17 . However, the addition of new sites from various research groups over the past two decades indicate that many sites at higher elevations display a zone of ice-enrichment below the ice table that extends to 1-2 m depth; below that depth, the GWC remains <30% with the exception of discrete ice lenses [25][26][27]69,70 (Fig. 2).…”

“…McMurdo Dry Valleys is from refs. [25][26][27]70 and from https:// soils.landcareresearch.co.nz/. Organic-rich soils is available online in Supplementary Data 1.…”

“…1). However, for example, clast-rich tills in the Richardson Mountains/Peel Plateau region in the Northwest Territories 18,19 , muck deposits in the Klondike region in Yukon 20,21 , fluvial gravels in the Mackenzie Delta 22,23 , silty colluvium near Salluit in Nunavik 24 and sandy-stony sediments in the MDV [25][26][27] often contain ground ice abundance similar to frost-susceptible soils, but were identified as regions with low-medium ice content. This suggests that there are factors other than particle size, sediment age, and climate that can lead to near-surface ice enrichment.…”

Cryostratigraphy of mid-Miocene permafrost at Friis Hills, McMurdo Dry Valleys of Antarctica – ERRATUM

“…Cambridge apologises for a publisher-introduced error during the production process of the above article (Verret, 2020).…”