Abstract:
A 12.7 m long sedimentary record recovered from Lake El'gygytgyn, located in a meteorite impact crater created 3.6 Ma in Late Cretaceous igneous rocks on Chukotka Peninsula, northeast Siberia, has been analysed for its palaeo- and rock-magnetic properties. Continuous high resolution (1 mm) measurements of magnetic susceptibility yielded successions of pronounced lows and highs. Analyses of the rock-magnetic properties by low and high temperature runs of magnetic susceptibility, determination of hysteresis parameters as well as IRM acquisition experiments, yielded a dominance of PSD (pseudo-single domain) magnetite in intervals of high magnetic susceptibility, whereas, due to selective magnetite dissolution associated with anoxic Lake water and/or pore water conditions during times of enhanced deposition of organic matter, haematite dominates within low susceptibility intervals in terms of mass percentage. Here however, magnetic properties are still dominated by magnetite. Five AMS (accelerator mass spectromentry) 14C ages, eight IRSL (infrared stimulated luminescense) ages together with preliminary pollen data suggest that variations in magnetite content reflect climatic variability of the last ∼300 ka with low (high) susceptibilities representing cold (warm) climates. This pattern, caused by a complex system of deposition, preservation or decomposition of organic matter and/or magnetic minerals, in turn can be correlated in detail to global climate archives such as the oxygen isotope records from Greenland ice cores and marine sediments, respectively. Thus, the sedimentary sequence recovered from Lake El'gygytgyn represents the longest continuous terrestrial climate record now available from the Arctic.