whole_RobertsDonna1998_thesis.pdf (11.97 MB)
Reconstruction of lake-water salinity from fossil diatom assemblages in saline lakes of the Vestfold Hills, Antarctica
thesisposted on 2023-05-27, 17:05 authored by Roberts, D
Polar lake environments provide an essentially undistubed ecosystem to research and their water chemistries are often the result of climatic influences throughout their histories. Salinity, in particular, has a clear relationship with changing precipitation and evaporation in polar lake environments, thus changes in lakewater salinity can be related to the climatic regime of polar lakes basins. By exploring the relationship between diatom assemblages and limnological environmental variables in Antarctic saline lakes, fossil diatom assemblages enable palaeo-lake water variables in these lake ecosystems to be quantified. Canonical correspondence analysis of the relationship between surface sediment diatom assemblages and measured limnological variables in thirty-three coastal Antarctic lakes revealed that salinity accounted for a significant amount of the variation in the distribution of these diatom assemblages, revealing its value for limnological inference models in this coastal Antarctic region. A weighted-averaging regression and calibration transfer function developed from this diatom salinity relationship enables the reconstruction of past lakewater salinity from fossil diatom assemblages. Application of this palaeosalinity reconstruction tool to four lake sediment cores collected from lakes representative of the range of current salinities in the Vestfold Hills (fresh to markedly hypersaline) allows the timing and extent of the salinity development of these currently different lake environments to be determined. Diatom stratigraphy of two lakes currently characterised by hypersaline and marine epilimnion lakewater salinity respectively revealed distinct changes in lake history. Initial lake assemblages are indicative of a freshwater community. Subsequent assemblages represent marine inlet and saline lake assemblages respectively. In both cores, core bottom assemblages produced a lakewater salinity of the order of 3 ‚ÄövÑ‚àû while core top assemblages produced a saline lakewater salinity of the order of 60 ‚ÄövÑ‚àû. Diatom stratigraphy of the currently hyposaline lake revealed a history of continual salinity increase (of the order of 3 ‚ÄövÑ‚àû to 25‚ÄövÑ‚àû) in this basin. Conversely, diatom stratigraphy of the freshwater lake revealed little salinity change throughout the core (~ 1‚ÄövÑ‚àû fluctuation) demonstrating the greater sensitivity of the saline lakes investigated as palaeoclimatic recorders. Salinity has a clear relationship with changing precipitation and evaporation in polar lake environments. Therefore, changes in lakewater salinity allow inferences to be made about the changes in a lake basins local climate. Cycles of increasing and decreasing salinity within one of the saline lake cores demonstrates the effectiveness of the diatom-salinity transfer function as a proxy for inferring changes in water level and effective precipitation. Palaeolake precipitation estimates from these salinity and water level reconstructions show no significant trends in precipitation are detectable throughout the past ~ 700 years. There is certainly no identifiable increase in precipitation in the past two centuries as would be expected with anthropogenically influenced warming in such a region, revealing the usefulness of this tool for palaeoclimatic analyses in Antarctic limnological regions.
Rights statementCopyright 1997 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (PhD)--University of Tasmania, 1998. Includes bibliographical references