Late Pleistocene and Holocene Paleolimnology of Two Mountain Lakes in Western Tasmania

Abstract

The analysis of diatoms from two lake-sediment cores from southwestern Tasmania that span the Pleistocene-Holocene boundary provides insight about paleolimnological and paleoclimatic change in this region. Both Lake Vera (550 m elevation), in west-central Tasmania, and Eagle Tarn (1,033 m elevation), in south-central Tasmania, have lacustrine records that begin about 12,000 years ago. Despite significant differences in location, elevation, and geologic terrane, both lakes have had similar, as well as synchronous, limnological histories. Each appears to have been larger and more alkaline 12,000 years ago than at present, and both became shallower through time. Fossil diatom assemblages about 11,500 years old indicate shallow-water environments that fluctuated in pH between acidic and alkaline, and between dilute and possibly slightly saline hydrochemical conditions (<100-2,000 mgll dissolved solids), probably under the influence of seasonal moisture stress. Beginning 11, 500 years ago, limnological conditions of shallow, dilute water of neutral pH prevailed, indicating reduction of moisture stress. A subsequent transition to diatom assemblages indicative of acidic and dystrophic (brown, nutrient-poor water) conditions about 10,000 years ago parallels the establishment of rain-forest vegetation and essentially modern climatic conditions with excess precipitation over evaporation. The synchroneity and similar character of the paleolimnological changes at these separate and distinctive sites suggests a regional paleoclimatic cause rather than local environmental effects. Latest Pleistocene climates were apparently more continental and drier than Holocene climates in southwestern Tasmania.