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

Published online by Cambridge University Press:  16 December 2020

Marjolaine Verret*
Affiliation:
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
Warren Dickinson
Affiliation:
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
Denis Lacelle
Affiliation:
Department of Geography, Environment and Geomatics, University of Ottawa, Ottawa, Canada
David Fisher
Affiliation:
Department of Earth Sciences, University of Ottawa, Ottawa, Canada
Kevin Norton
Affiliation:
School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand
Hannah Chorley
Affiliation:
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
Richard Levy
Affiliation:
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand GNS Science, Lower Hutt, New Zealand
Tim Naish
Affiliation:
Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand

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.

Information

Type
Earth Sciences
Copyright
Copyright © Antarctic Science Ltd 2020

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