Holocene palaeoenvironmental conditions in NE Bulgaria uncovered by mineral magnetic and paleomagnetic records of an alluvial soil

Abstract

Retrieving well-dated terrestrial archives of Holocene climate change is fundamentally important for building robust climate models and predictions. In this study we obtained records of paleomagnetic direction and relative paleointensity of the Earth's magnetic field from an alluvial soil situated on a flood river terrace close to the well-dated and stratigraphically confined Chalcolithic mound near the village of Koprivetz in NE Bulgaria. Anisotropy of magnetic susceptibility data revealed a coherent imbricated magnetic fabric reflecting the effects of water flow in the lower alluvial clays and the direction of delluvial sedimentation from the slope in the upper soil horizons. Variations of declination, inclination and relative paleointensity along depth of the soil profile were correlated to the archaeomagnetic secular variation curves for Bulgaria, using the age of the earliest archaeological stratigraphic horizon as the main tie point. Based on this correlation, an age model was constructed and temporal variations of environmental magnetic parameters were examined for their suitability as paleoclimate proxies. The ratio of frequency dependent susceptibility to anhysteretic susceptibility (χfd/χARM) is a reasonable proxy for paleoprecipitation due to its close resemblance to paleo-flood records from the Northern and Southern Alps. Events of increased flood intensities during the late Holocene (post – 4700 y BP) are registered through χfd/χARM and reveal good correspondence to the flood records of rivers in Southern Alps and Carpathians. The ratio of isothermal remanent magnetization after 20 mT alternating field demagnetization (IRM20mT) normalized to the full IRM showed good consistency with the GISP2 ice record of temperature variations in Greenland during the Holocene. Six major cold incidents during the last 7000 y BP with the major one at 4500 y BP are evidenced. The obtained results suggest that climate at mid-latitude SE Europe is sensitive to the changes in North Atlantic circulation.