Antarctic ice sheet and climate evolution during the mid-Miocene

• Main Author: Hannah Chorley
• Format: Thesis
• Language: unknown
• Published: 2021
• Subjects: Sedimentology; Stratigraphy (incl. Biostratigraphy and Sequence Stratigraphy); Geology not elsewhere classified; Antarctic Ice Sheet; Miocene; Friis Hills; Transantarctic Mountains; Carbon dioxide; Model-data comparison; Stratigraphy; 040310 Sedimentology; 040311 Stratigraphy (incl. Biostratigraphy and Sequence Stratigraphy); 040399 Geology not elsewhere classified; 960306 Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts); Antarctic; McMurdo Dry Valleys; East Antarctic Ice Sheet; Antarc*; Ice Sheet
• Online Access: https://doi.org/10.26686/wgtn.14150105.v1; https://figshare.com/articles/thesis/Antarctic_ice_sheet_and_climate_evolution_during_the_mid-Miocene/14150105

The mid-Miocene provides an important example relevant to the response of the East Antarctic Ice Sheet (EAIS) to future anthropogenic climate change. Geological observations and earth system modelling show a broad link between declining carbon dioxide (CO2) concentrations and increasing size and sensitivity of ice sheets in the past. Future projections show CO2 concentrations could reach up to 1000 ppm before the end of the century, with global temperatures 4-5°C warmer - a climate not seen since the mid-Miocene. This time period is therefore becoming increasingly important to understanding future Antarctic Ice Sheet (AIS) response, as CO2 concentrations are already at Pliocene levels (∼400 ppm). An improved, more detailed understanding of the response of the AIS to past climatic variability provides important context for interpreting how the AIS will respond to future climate change under high CO2 scenarios. A dynamic EAIS characterised the mid-Miocene, with major variations in both volume and extent of terrestrial and marine ice sheets. While global climate remained warmer than present-day throughout, this interval was punctuated by an episode of unusual warmth within the Miocene Climatic Optimum (MCO, ∼17-15 Ma). The MCO is one of the warmest intervals since the onset of Antarctic glaciation, with CO2 concentrations of up to 840 ppm during peak warmth and coastal regions characterised by temperate vegetation and mean summer temperatures (MST) of up to ∼10°C. This warmth terminated with major cooling and ice expansion across the mid-Miocene Climate Transition (MMCT, ∼14.8-13.8 Ma). A ∼50 m thick ice-cemented terrestrial glacial sequence was recovered in drill cores from the Friis Hills, McMurdo Dry Valleys in 2016. A chronostratigraphic framework for the cores based on magnetostratigraphy, 40Ar/39Ar isotopic ages, and limited biostratigraphic constraints, revealed 15 sedimentary cycles of the advance and retreat of a temperate alpine glacier system between ∼15.1-13.8 Ma. Each cycle consists of traction tills ...