Reconstructing 15 Myr of environmental change in the McMurdo Dry Valleys through permafrost geochemistry

• Main Author: Marjolaine Verret
• Format: Thesis
• Language: unknown
• Published: 2021
• Subjects: Isotope geochemistry; Organic geochemistry; Sedimentology; Geomorphology and earth surface processes; Friis Hills; Antarctica; ultraxerous; stable upland zone; carbon; nitrogen; permafrost; ground ice; Miocene; Beryllium-10; 040203 Isotope Geochemistry; 040204 Organic Geochemistry; 040310 Sedimentology; 040607 Surface Processes; 960306 Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts); 960399 Climate and Climate Change not elsewhere classified; School: School of Geography; Environment and Earth Sciences; Unit: Antarctic Research Centre; Degree Discipline: Physical Geography; Degree Discipline: Geology; Degree Name: Doctor of Philosophy; Degree Level: Doctoral; Surface Processes; Antarctic; McMurdo Dry Valleys; Taylor Valley; Antarc*; Ice; Ice Sheet; Tundra
• Online Access: https://doi.org/10.26686/wgtn.14776521.v1; https://figshare.com/articles/thesis/Reconstructing_15_Myr_of_environmental_change_in_the_McMurdo_Dry_Valleys_through_permafrost_geochemistry/14776521

The McMurdo Dry Valleys of Antarctica are the largest ice-free region in Antarctica. Valley downcutting by major outlet glaciers and post-glacial uplift since the mid-Miocene have resulted in predominantly younger surficial sediments in the low elevation, coastal areas and significantly older sediments in high elevation, inland areas. The hyper-arid conditions that prevail in the high elevations (> 1000 m a.s.l.) of the McMurdo Dry Valleys have protected these surfaces from alteration and weathering, and provide important sediment records of paleoenvironments dating back to the early Miocene. The Friis Hills (77°45’S, 161°30’E, 1200–1500 m a.s.l.) are a 12 km-wide inselberg situated at the head of Taylor Valley. This unique location allowed Miocene-age sediments to be preserved and protected from subsequent ice sheet expansions. Permafrost within these sediments is potentially the oldest on Earth. As sediments accumulate in periglacial environments, permafrost aggrades with minimal lag time and potentially preserves sediments, organic material and ground ice. The 2016 Friis Hills Drilling Project retrieved a ∼50 m thick permafrost sequence, which not only consists of an archive of Antarctic environmental changes from approximately 14–15 Ma but also records the paleoenvironmental changes of the Neogene and provides insight on the modern hyper-arid environment. The main objective of this project is to understand the unique geochemical characteristics of these permafrost cores and document 15 Myr of change in the upper elevations of the McMurdo Dry Valleys. Paleoenvironmental reconstructions of interglacial periods suggest a tundra-like environment in the high elevations of continental Antarctica through the mid-Miocene. Plants such as lichens, liverworts, mosses, grasses and sedges, dicots and Nothofagaceae occupied the Friis Hills during the mid-Miocene. The δ13C signal of C3 plants (-25.5 ± 0.7 ‰ VPDB) corresponds to a semi-arid environment with a mean annual precipitation ranging from 300 to 850 mm yr-1. The ...