The response of Antarctic ice volume, global sea-level and southwest Pacific Ocean circulation to orbital variations during the Pliocene to Early Pleistocene

• Main Author: Patterson, Molly O'Rourke
• Other Authors: McKay, Robert, Naish, Timothy
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Victoria University of Wellington 2014
• Subjects: Antarctica; Southern Ocean; Pacific Ocean; Antarctic; East Antarctic Ice Sheet; New Zealand; Pacific; The Antarctic; Wilkes Land; Antarc*; Ice Sheet; Iceberg*; Sea ice
• Online Access: http://researcharchive.vuw.ac.nz/handle/10063/3664

This thesis investigates orbitally-paced variations in the extent of East Antarctic Ice Sheet (EAIS), and the “downstream” influence of these ice sheet variations on ocean circulation and sea level variability during the Pliocene and Early Pleistocene - a time period characterised by a major global cooling step that culminated in the development of a bipolar glaciated world. Three unique records are examined from (1) the Antarctic margin, (2) the southwest Pacific Ocean, and (3) shallow-marine sedimentary strata exposed in Wangnaui Basin, New Zealand. The Integrated Ocean Drilling Program (IODP) Site U1361 recovered a continuous sedimentary Early Pliocene to Early Pleistocene (4.3 to 2.0 Ma) record from the lowermost continental rise on the Wilkes Land margin offshore of the EAIS. A facies model and stratigraphic framework were developed that allowed for the identification of glacial advances (massive and laminated mudstones) and retreats (diatom-rich mudstones) across the continental shelf, with evidence for prolonged retreats spanning several glacial to interglacial cycles throughout the Pliocene. These cycles are followed by an extensive Early Pleistocene interval (~2.6 Ma) of diatom-rich mudstone with evidence for reworking by bottom currents, interpreted to be the consequence of downslope density currents associated with increased sea ice production after 2.6 Ma. Frequency analysis on Iceberg Rafted Debris (IBRD) from Site U1361 reveals that under an Early Pliocene warm climate state (4.3 to 3.3 Ma), that ice discharge off the EAIS occurred in response to climate change paced by the 40-kyr cycles of obliquity. Whereas, the colder climate state of Late Pliocene to Early Pleistocene (3.3 to 2.0 Ma) resulted in a transferral of orbital variance to 20-kyr-duration, precession-dominated variability in IBRD preceding the development of a more stable marine-based margin of the EAIS at ~2.6 Ma, which is hypothesized to reflect the declining influence of oceanic forcing as the high-latitude Southern Ocean cooled ...