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Molecular and Isotope-Proxies

Science Partnerships for the Assessment of Complex Earth System Processes - SPACES

GeoArchives: Signals of Climate and Landscape Change preserved in Southern African Geoarchives

Background

Climate of southern Africa is strongly influenced by global factors. The amount of precipitation and its seasonality in particular are controlled both by marine currents and by atmospheric cycles. Therefore, global change can have strong impacts on local environmental conditions. Reconstructions of past climate change can help to understand these processes. However, climate records from southern Africa are still scarce, mainly due to missing conventional geoarchives like lakes. The project GeoArchives uses alternative sedimentary archives in order to fill in these gaps.

The collaborative project GeoArchives is part of the BMBF funded program SPACES "Science Partnerships for the Assessment of Complex Earth System Processes". The project aims at the analysis of the impact of anthropogenic and natural processes, like climate change und erosion, on ecosystems and land use in southern Africa. In sub-project SP3, “Coastal lagoons and continental salt pan sediments – Holocene climate-ecosystem archives“, these two types of sediment archives from Namibia and South Africa are used to reconstruct ecologic and climatic changes during the late Pleistocene and Holocene. To achieve this, we are using methods of sedimentology, organic geochemistry and geomicrobiology.

Overview map Namibia, Geoarchives

Continental salt pans are local depressions with diameters ranging between a few km² up to large areas, which are flooded during strong precipitation events which can occur during summer. The organic geochemical approach within this sub-project is to analyze leaf wax compounds such as n-alkanes, n-alkanols, and n-alkanoic acids. Their distribution patterns and isotopic composition allows conclusions on the surrounding vegetation, which reflects the regional climate at the time of their formation. Compound specific analyses of the deuterium isotopic composition can give additional information on water availability.In the Namibian coastal desert coastal pans and lagoons belong to the most important sedimentary environments. In these settings, marine biomarkers are in the focus of research, in addition to plant wax derived compounds. They can help reconstructing the intensity of coastal upwelling in the past. Upwelling of deeper water masses lead to cool sea surface temperatures which again influence the transport of humidity to higher air masses and thus control precipitation in the hinterland.

Goals

  • Understanding of the relationship between changes in sea surface temperatures and precipitation patterns in the coastal area and the hinterland
  • Interpretation of regional, climatic, and ecologic variability in a global context
  • Determining the applicability of paleo-limnologic methods used in organic geochemistry on salt pans
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