The Termination of the Last Glacial Cycle in eastern Australia: A High Resolution, Multiproxy Analysis

• Main Author: Lynda Petherick
• Format: Thesis
• Language: English
• Published: The University of Queensland, School of Geography, Planning & Env Management 2011
• Subjects: Last Glacial Cycle termination; Last Glacial Maximum; extended LGM; Climatic variability; environmental variability; Subtropical Australia; Southern Hemisphere; lake sediment; multiproxy; late Quaternary; 040605 Palaeoclimatology; 040606 Quaternary Environments; Almond; Kershaw; New Zealand; Queensland; Antarc*; Antarctica
• Online Access: https://espace.library.uq.edu.au/view/UQ:275374/s4082154_phd_abstract.pdf; https://espace.library.uq.edu.au/view/UQ:275374/s4082154_phd_finalthesis.pdf; https://espace.library.uq.edu.au/view/UQ:275374

A continuous, high resolution (average ca. 22 year) record encompassing the termination of the Last Glacial Cycle (LGC) (defined here as ca. 31 – 18 kyr) has been developed using multiple proxies (viz. sediment flux, grain size, moisture content, pollen and charcoal) in lake sediment from Tortoise Lagoon (TOR), North Stradbroke Island (NSI), Queensland, Australia. This record is one of only two available from the lowland subtropics of Australia which are continuous through the termination of the LGCLGC. As such, the TOR record assists in bridging an extensive spatial gap between the records of palaeoclimatic and palaeoenvironmental variability from the tropical north and temperate south. The presence of key pollen taxa (e.g. Asteraceae (Tubuliflorae) and spineless Asteraceae, which are common indicators of glacial conditions in Australia) at TOR indicates significantly cooler temperatures (mean annual temperature up to 11oC lower than today) extending into the subtropics. Pollen taxa present also indicate mean annual precipitation up to 65% lower than modern. Similarities between the vegetation at TOR during the Last Glacial Maximum (LGM) and that at temperate sites e.g. Caledonia Fen, Victoria (Kershaw et al. 2007b), Redhead Lagoon, New South Wales (Williams et al. 2006) and Barrington Tops, New South Wales (Sweller and Martin 2001) suggests that this record reflects regional conditions across southeastern Australia. The TOR record also correlates well with that from nearby Native Companion Lagoon which suggests that the LGM was actually an extended period of ca. 8 – 10 kyr, characterised by 2 periods of increased aridity (ca. 30 – 26.5 kyr and 21 – 19.5 kyr) (Petherick et al. 2008a). A growing number of records from across the Southern Hemisphere e.g. New Zealand (Suggate and Almond 2003; Alloway et al. 2007; Newnham et al. 2007a), Chile (Denton et al. 1999b), Antarctica (Röthlisberger et al. 2002; EPICA 2006) and Australia (Smith 2009) also show evidence that the LGM encompassed a longer period of time than traditionally accepted, and was not uniformly cool and dry. As such, it is suggested that the early onset of the termination of the LGC in the Southern Hemisphere occurred from ca. 35 – 30 kyr, and was possibly driven by summer insolation minima in the high southern latitudes. In addition, trace element compositions of inorganic deposits archived in the TOR sediments were used to provenance dust to continental source areas. Such provenance allowed the reconstruction of major dust transport pathways to NSI during the LGM, which in turn allowed associated synoptic scale conditions to be suggested. The position and strength of dust transport pathways for eastern Australia during the termination of the LGC provides new insights into climatic conditions in the region. Our reconstructions show that latitudinal westerly wind circulation was dominant during the LGM in two phases, suggesting an equatorward shift in the position of the westerlies. Westerlies appeared to shift poleward during the interstadial period, when southeasterly trade winds became more influential on NSI.