HR: 1340h
AN: GP53B-1215    [Abstracts]
TI: Magnetic Fingerprint for Holocene Climate Change in a High Alpine Lake
AU: * Hirt, A M
EM: hirt@mag.ig.erdw.ethz.ch
AF: ETH-Zurich, LNM, Institute of Geophysics Schafmattstrasse 30, Zurich, CH-8093, Switzerland
AU: Koinig, K A
EM: Karin.Koinig@uibk.ac.at
AF: University of Innsbruck, Institute of Ecology Technikerstrasse 25, Innsbruck, A-6020, Austria
AB: High alpine lakes provide high-resolution archives for environmental change since steep climatic gradients can enhance the effect of small climatic shifts, and human influence is minimal. The magnetic properties of lacustrine sediments from Schwarzsee ob Soelden (SOS), a high alpine lake located in western Austria, were evaluated and compared with other climate proxies. The depth of this oligotrophic lake is currently 17 m and the lake covers 3.05 ha. It lies above the present tree line and the catchment area is characterized by fine-grained crystalline rock and scree with a sparse soil cover. A 159 cm core from the deepest anoxic part of the lake covers the past 10,000 years. The magnetic parameters; i.e., magnetic susceptibility, isothermal remanent magnetization and anhysteretic remanent magnetization, show a good correlation with Fe content. The mineralogy of the lacustrine sediments indicates four units: (1) the bottommost 6 cm, represent the weathered country rock and contain pyrite; (2) the following 14 cm of bottom sediments, consist of clays, feldspars, and quartz; (3) the next 120 cm, contain siderite in addition to the clay, feldspar and quartz; and in the uppermost 19 cm of sediment siderite is again absent. The lowest unit has a low concentration of low coercivity, ferromagnetic phases. The second unit has the highest concentration of ferromagnetic phases, with slightly higher coercivity. There is an abrupt change in the magnetic properties around 9000 yr BP. The next 140 cm of sediments are dominated by a low coercivity, ferromagnetic phase, and the constant values for the S-ratio and ARM/IRM suggest that its grain size spectrum does not vary greatly. The only exception is in a small zone around 5000 yr BP, which is associated with a rapid cooling event.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting