Terrigenous organic matter in Holocene sediments from the central Baltic Sea, NW Europe

The Baltic Sea is an epicontinental sea surrounded by a catchment in boreal and sub-boreal vegetation zones. The isotopic composition (δ13C) of organic carbon was in the range of −30‰ to −20‰, but, contrary to our expectations, had no statistically significant relation to lignin oxidation product yields (0.4 to 10 mg g−1 TOC) in a large set of Baltic Sea surface sediments. The isotopic ratio thus may be inappropriate as an indicator for marine versus terrestrial organic carbon input into the Baltic Sea. As in surface sediments, we find no correspondence between lignin biomarker abundance (0.3 to 6 mg g−1 TOC) and δ13C (−30‰ to −24.5‰) of organic carbon in sediments from a core which brackets the late glacial and the Holocene. The relative contribution of terrestrial carbon, as estimated from lignin oxidation product analyses, increased steadily as soils and forests developed. Transgressive events of lake and marine stages are marked by enhanced input of terrestrial organic carbon. There was no evidence that the terrestrial organic matter was altered significantly after sedimentation because, although (Ad/Al)V and (Ad/Al)S varied between 0.3 and 0.7, there was no trend of increasing values downcore. The amount and the composition of the sedimentary lignin as indicated by S/V (0.3 to 0.9) and C/V (0.2 to 5.6) changed according to the development of the vegetation after deglaciation and the effects of human activity. In the Late Holocene, signals in lignin input and composition thus correlate with the development of the vegetation, with hydrographic changes and with human activities, particularly with deforestation events.