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Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct 14C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.
Analysis of a 1.5 m thick sediment sequence from Midge Lake, Byers Peninsula, Livingston Island, shows that the lake and its catchment have undergone significant changes during the last 4000 years. Radiocarbon dating (AMS), sediment lithology, and microfossil analyses indicate that the lake was deglaciated over 4000 14C years ago. Distinct peaks in accumulation rates of sediment, Pediastrum algae, pollen and spores, as well as changes in the diatom assemblage, suggest significant environmental changes between ca 3200 and 2700 y BP. These changes are interpreted as reflecting a milder and more humid, maritime climate. The increased humidity can explain independent observations of glacier growth during this period. The combined data also indicate that between ca 1500 and 500 y BP the area might have experienced more continental conditions with slightly colder and drier climate than today. Since the 14C dates from the Midge Lake sediments are regarded as reliable and the sediment sequence is rich in tephra layers this sediment sequence will be critical for a forthcoming tephra chronology of the region.
Sediment from Lake Boeckella, Antarctic Peninsula, is richer in Ca, Cd, Cu, P, Sr and Zn than that of six other lakes in the area. The elements originate from Adélie penguin (Pygoscelis adeliae) guano on the lake shores. Changing Cu and P concentrations in the lake sediment are used as a proxy for penguin influence on the lake sediment from ca. 5850 bp to present. A 14C dating model suggests that the 14C correction factor in the lake sediments depends on the penguin proxy, the apparent age of the penguin guano and the amount of particulate carbon originating from the carbon-bearing shales in the watershed. Glacial meltwater and dissolved carbonates do not contain enough “old” carbon to contribute significantly to the correction factor. Ages corrected with the 14C dating model agree with the depth vs. age curve based on independently 14C-dated tephra horizons. The reservoir effect has been constant since at least 5800 bp, implying long-term stability of the currents and water masses in the area. The existing chronology for Lake Boeckella has been recalculated. The period of glacial advance, previously thought to have culminated at 5000 bp, is now thought to have culminated at 4700 bp; deglaciation of the area is thought to have occurred at 6300 bp instead of 8680 bp.
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