Cause-and-effect in Mediterranean erosion: The role of humans and climate upon Holocene sediment flux into a central Anatolian lake catchment
Résumé
The debate in historical geomorphological studies about the causes of erosion in regions such as the Mediterranean has been long-standing. The relative roles of climate change and human impacts can be difficult to disentangle in the absence of highly resolved chronologies. Here we reconstruct the erosion history of a small lake catchment in central Anatolia, located on the edge of one of the Mediterranean's most iconic badland landscapes in Cappadocia. Because these lake sediments are annually laminated, precisely dating clastic inwash layers and calculating recurrence intervals and flux rates is possible. Lake cores have been analysed for μXRF elemental geochemistry and via thin sections, along with proxies for hydroclimate (oxygen isotopes) and land cover (pollen). Peaks in titanium, along with other detrital elements, and changes in clastic layers indicate increased sediment influx into Nar Lake between 9300 and 8000 cal BP (ceramic Neolithic, when obsidian mining took place nearby) and again, more importantly, during the last 2500 years (Iron Age to modern), the latter exhibiting three phases of enhanced catchment erosion. Multiproxy comparisons show that these phases were related primarily to periods of increased human impact on vegetation and soils around the lake. Most sediment influx has been in the form of turbidites, linked to the presence of a fan delta at the lake edge, although this store does not appear to have significantly delayed sediment delivery from eroding hillslopes to the lake bed. The marked increase in detrital influx during the late Holocene implies that badland development in the lake catchment is recent and largely anthropogenic, rather than ancient and of climatic causation, and probably involving stream capture. The record also shows that sediment influx diminished markedly at times when human land use disintensified, which in turn indicates that hillslope degradation is reversible with appropriate land management.
