Using 210pb-data and paleomagnetic secular variations to date anthropogenic impact on a lake system in the Western Cape, South Africa

Swartvlei is one of the most thoroughly investigated lacustrine coastal systems in South Africa. However, studies regarding the most recent past (i.e., the last 30-40 years) examining anthropogenic impacts on sediment deposition are missing completely. This study, covering the past 400 years, provides evidence for distinct environmental changes during this time most likely related to anthropogenic activities such as farming or water abstraction. A decrease in marine influence is observed starting somewhat earlier but was potentially supported by human management activities. In this respect age-depth-modelling is an important issue and needs further investigations in many coastal geoarchives of South Africa. Therefore, a multi-dating approach using several methods is suggested since errors in the chronology distinctly impact paleoenvironmental reconstructions (timing, flux rates etc.). In this context this is the first time that paleomagnetic secular variation data obtained from South African sediment records are used for dating purposes which is the only approach to establish a reliable chronology for recent sediments in this system.