Year

2019

Degree Name

BEnviSci Hons

Department

School of Earth, Atmospheric & Life Sciences

Advisor(s)

Tim Cohen

Abstract

Long records of climate variability which extend beyond the Last Glacial Maximum (LGM) are rare in Australia. However, the nature of lacustrine settings as sedimentary sinks often provide excellent archives of environmental and climatic variability over long time scales. Thirlmere Lakes are a sequence of five freshwater lakes within the Greater Blue Mountains World Heritage area of NSW and are situated in a meander channel of a palaeo-river. The unusual geomorphic setting of the lakes has produced a deep archive of sediment and provides a long record of climate variability extending beyond the LGM. The Thirlmere Lakes have also undergone an observable drying trend since the 1970's. The reduction in lake level poses the question as to whether the drying is part of natural hydrological variability or unprecedented water loss.

This study presents a ~100ka long palaeo-environmental interpretation of Lake Werri Berri, the largest of the Thirlmere Lakes, and compares it to available records for the wider lake system. A focus of this study is to investigate whether drying observed at the lakes is unique or if similar episodes have occurred in the past. It also examines how environmental archives are produced at Thirlmere Lakes, from the catchment (ridge crest and hillslope) to the sink (lake floor). Stratigraphic and elemental analysis from four lake cores and two hillslope cores indicates Lake Werri Berri has undergone substantial hydrological variability in the past. The results demonstrate for the first time that a distinct drying phase during the LGM was found to occur across Lake Werri Berri and the adjacent lakes. XRD analysis shows sediment deposited during this phase has a different minerogenic signature to other lake sediments and suggests a change in the source of material entering the lake at this time. An investigation of organic material (in particular charcoal) show down-profile and down-slope buffers in the supply of charcoal to the sink with sediment being temporarily stored on the lower hillslopes and sporadically liberated during periods of high wildfire and storm activity. This study shows that charcoal delivery processes therefore need to be considered when interpreting charcoal records. This study extends the knowledge of palaeo-environmental and climatic changes that have occurred in the Sydney Basin region over the last glacial cycle.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.