Linking marine dust records to Saharan landscape evolution during the Holocene: a theoretical study

• Main Author: Egerer, S.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Hamburg 2018
• Subjects: North Atlantic
• Online Access: http://hdl.handle.net/21.11116/0000-0000-8E3E-C; http://hdl.handle.net/21.11116/0000-0000-8E40-8

Marine sediment records show an abrupt and large increase in North Atlantic dust deposi- tion towards the end of the African Humid Period (AHP) about 5 ka BP. How this abrupt shift in dust deposition is linked to Holocene North African landscape and climate change is still under debate. Within the scope of this thesis, we simulate the North African dust cycle from the mid-Holocene until present-day using the coupled aerosol-climate model ECHAM6-HAM2. We thereby identify drivers of the change in dust deposition and set the dynamics of dust deposition in context to North African landscape evolution. In a rst step, we simulate the pre-industrial and mid-Holocene dust cycle, where vegeta- tion and lake cover as well as orbit and ocean conditions are prescribed. Consistent with marine sediment records, our simulations show that North Atlantic dust deposition uxes were two to three times lower during the mid-Holocene compared with pre-industrial uxes. In a sensitivity study, we identify enhanced vegetation cover and extended lake surface area to be the main cause of the reduced dust cycle during the AHP as they cover dust source areas and alter the atmospheric circulation. In a second step, we aim to understand the dynamics of the dust cycle. Therefore, we test the hypothesis that gradual changes in North African landscape result in an abrupt shift in North Atlantic dust deposition. This could have been caused either due to the nonlinearity in dust activation or due to a heterogeneous distribution of major dust sources. To explore these two arguments, we prescribe a gradual decline of North African vegetation and lake cover in two series of simulations. In contrast to our hypothesis, we do not nd evidence for an abrupt increase in simulated dust deposition as seen in the marine records. Our results rather point to a rapid large-scale retreat of vegetation and lakes in the area of signicant dust sources in the northwest Sahara. Finally, we perform time slice simulations including dynamic vegetation. We nd a rapid ...