DATE2016-05-31 14:24:22
AUTHORSJens Holtvoeth (1,2), Harriet Copsey (2), Danielle Rushworth (1), Sophie Flack (1), Karina Scurupa Machado (1,3), Richard Pancost (2), Bernd Wagner (4), George Wolff (1)
  1. University Of Liverpool, School Of Environmental Sciences Liverpool (United Kingdom)
  2. University Of Bristol, School Of Chemistry Bristol (United Kingdom)
  3. University Of Parana Curitiba (Brazil)
  4. University Of Cologne, Institute Of Geology And Mineralogy Cologne (Germany)
ABSTRACTRecent surveys of modern terrestrial organic matter pools (plant matter, soils) in the Ohrid Basin provided an organic geochemical fingerprint for the major sources of lipid biomarkers in the sediments of Lake Ohrid. This allowed to reconstruct terrestrial habitat dynamics through changes in the relative contributions from the two major organic matter pools, vegetation and soils. Relatively increased supply of soil-derived lipid biomarkers occurs during periods of rapid habitat change, in particular, vegetation recession and associated destabilisation of soils. Naturally, this would occur in response to climatically controlled hydrology changes, however, land-use change can have a similar impact. We present geochemical proxy data across three well-known Holocene climate fluctuations: the 8.2 ka event, the 4.2 ka event and the transition from the Dark Ages (DA) to the Medieval Warm Period (MWP) as observed in a sediment core near the southern shores of Lake Ohrid. The latter two also coincide with periods of major social changes as well as advances in technology. During the 8.2 ka event, the biomarker data suggests two phases of soils depletion that likely correspond to the two major freshwater pulses from North American ice-dammed lakes and the dry conditions these caused in large parts of Central and Southern Europe. The 4.2 ka event manifests itself in the eastern Mediterranean and the Middle East as a prolonged period of droughts that were responsible for the collapse of some of the early Bronze Age empires. While increased soil supply towards Lake Ohrid at the beginning and the end of this climatic excursion may result from the natural readjustment of the terrestrial habitat, increased soil erosion at the centre of this period appears to coincide with archaeological evidence for an inflow of people from N’ Greece during the mid-Bronze Age and associated land-use change. During the DA-MWP transition we again observe increased soil erosion. This period coincides with significant socio-economic changes in the Ohrid Basin. Between the years 900 and 1010, the monastery of St Naum was founded, the town of Ohrid became the capital of the Bulgarian Empire and people moved from a defensive hill-top settlement above the modern town of Pogradec towards the lake shores. We hypothesise that the establishment of the St Naum monastery in the vicinity of the study site corresponds to the introduction of large-scale agricultural production and associated soil erosion.