TASCLIM · High-resolution quantitative climate reconstructions for understanding current trends: the past 2000 years of Tasmanian climate variability

High-resolution quantitative climate reconstructions for understanding current trends: the past 2000 years of Tasmanian climate variability

The overall objective of the TASCLIM project was to use in-situ reflectance spectroscopy on lake sediment cores to develop a series of high-resolution quantitative reconstructions of temperature and precipitation for different climatic regions of Tasmania. The specific objectives of TASCLIM were to: (i) systematically explore the potential scope and limitations of in-situ reflectance spectroscopy as a tool for developing high-resolution, quantitative temperature and precipitation reconstructions in a variety of lake sediments from Tasmania; and (ii) produce a series of quantitative high-resolution temperature and precipitation reconstructions to investigate Tasmanian climate variability during the past 2000 years. This involved extensive fieldwork in Tasmania during the summers of 2009 and 2010 to collect 14 sediment cores from seven lakes in different regions of Tasmania. These were brought back to the University of Bern where the analyses were undertaken. One sediment core from each lake was initially dated (using 210Pb and 137Cs) to determine which lakes had high enough sedimentation rates to develop the high resolution chronologies required for the calibration period (i.e. AD 1911-2009). Of the seven lakes studied collected, three did. These were analysed further to assess their potential for developing quantitative climate reconstructions. All sediment cores were successfully scanned using in-situ reflectance spectroscopy in the visible spectrum (VIS-RS, 380-730 nm). This provided the data for exploring the potential of in-situ reflectance spectroscopy. Extensive statistical analyses were then undertaken to develop calibration periods (AD 1911-2009) for all three sediment cores using VIS-RS data and meteorological data. This showed that for two of the three sediment cores VIS-RS data could be used to develop high resolution quantitative precipitation or temperature reconstructions. These two sediment cores were focused on for the remainder of the project. The calibration periods for each sediment core were applied down the rest of each sediment core to develop a high resolution quantitative annual precipitation reconstruction for northwest Tasmania, and a high resolution quantitative annual temperature reconstruction for southeast Tasmania. The changes in each record were compared to other records from Tasmania, New Zealand and South America to investigate how Tasmanian climate variability has changed in the last 1000-2000 years. The most significant results of TASCLIM have been to develop the first quantitative high resolution precipitation and annual temperature reconstructions for Australia. The precipitation reconstruction showed that rainfall in northwest Tasmania has been highly variable over the last 2000+ years, mostly as a result of fluctuations in the position and strength of the Southern Hemisphere westerly winds. The temperature reconstruction showed that temperature variability in southeast Tasmania has been similar to temperature variability in New Zealand and South America over the last c. 1000 years. Both of these climate reconstructions have contributed valuable information for understanding climate variability in the Southern Hemisphere, which may be used in the future for regional and hemispheric assessments of climate variability over the last 1000-2000 years.

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