Hans von Suchodoletz

Landscape aridification in Central Germany during the late Weichselian Pleniglacial – results from the Zauschwitz loess site in western Saxony

In Zauschwitz (Western Saxonian loess area, Central Germany), a ca. 7 m thick loesspalaeosol sequence underlain by fluvial gravels and sands was investigated in order to study regional palaeoenvironmental changes during the late Weichselian Pleniglacial. The lithostratigraphic classification of the loess-palaeosol sequence was combined with polymineral fine grain luminescence dating using the pIRIR290 approach, and correlated with similar loess-palaeosol-sequences from Central Saxony. Doing so, we obtained information about a climatic shift from more humid to more arid conditions during the late Pleniglacial, due to changes in the landscape dynamics of the study area: At ca. 30 ka, braided river floodplain accumulation of the nearby Weisse Elster river was followed by a phase of decreased fluvial activity, allowing initial loess deposition on top of the fluvial sands and gravels. This period was characterized by cold but still quite humid conditions, as indicated by reworked loess and the occurrence of several tundra gley soils. Subsequently, a cold and more arid period of dust accumulation followed after ca. 22 ka. Intensive anthropogenic activity almost totally redeposited the Holocene black soil, demonstrating the attractiveness of the fertile loess area for early human settlement.

North Atlantic influence on Holocene flooding in the southern Greater Caucasus

In the context of global climate change, flooding becomes an increasingly serious threat to modern societies, and future flooding can only be understood using long-term geological flood records also encompassing Holocene climate variability. Unlike other regions, Holocene flooding in the Caucasus region is only poorly understood so far: Whereas some rivers originating from the Lesser Caucasus were investigated, no studies exist about rivers originating from the Greater Caucasus. This study investigated the Holocene fluvial dynamics of the upper Alazani River in the southern Greater Caucasus using chronostratigraphic and sedimentologic methods applied to a fluvial sediment-paleosol sequence. By comparing these data with other paleoenvironmental and regional recent hydroclimatic data, we aimed to identify the main drivers of Holocene flooding in the southern Greater Caucasus. Our study shows a link between fluvial sedimentation around 7.3, 5.4, 3.8–2.9 and around 1.7 cal. ka BP and North Atlantic Bond events. Although probably caused by a discharge maximum during spring, fluvial sedimentation is coeval with low regional spring precipitation. As supported by recent hydroclimatic data, intensified floods during Bond events could possibly be explained with more intensive precipitation but also a prolonged snow season during colder winters. The latter would lead to more spring meltwater and thus more intensive spring discharge. Consequently, given increasing annual temperatures because of human-caused global warming, the flood maxima of pluvio-nival rivers in the southern Greater Caucasus may be expected to decrease during the next decades. Our findings underline the need of geological flood records to understand future flood patterns of rivers in mountain regions with complex runoff regimes.