Sources and sinks for dust in Europe: Examples for climatic and geomorphological induced changes in the European loess and its deposition

The local geomorphological setting of sink areas strongly influences the distribution, preservation and thickness of loess sequences. For example, high accumulation and preservation occurs in depressions or on the leeward slope of topographic barriers. The sediment availability depends on the distance to source areas, such as large river systems, dry shelves, and glacio-fluvial outwash plains at the margins of ice sheets and glaciers. Vegetation density in these areas also governs the amount of dust that can be deflated, as vegetation increases surface roughness and acts as a dust trap, fixing the sediment. The most well-developed loess sequences were formed where alluvial terraces intersect slopes in stepped terrace systems, as seen in the valleys of the Dnieper, Danube and Rhine rivers in Europe, among others¹. Deflation of dust from various source areas, followed by deposition and reworking in different geomorphological settings results in a mixture of the accumulated material, which complicates the reconstruction of the original source areas.

Under favorable preservation conditions, such as in the Dehner Dry-Maar, heavy mineral analysis of lacustrine sediments has enabled the distinction of phases of dust inputs from local, regional and remote source areas². During phases with denser vegetation and forest cover, local sources are important; however, during the last 40 k years, when vegetation was mostly less dense, distant dust sources such as the dry North Sea shelves and reworked loess deposits played a major role. Loess deposits exhibit different facies due to processes associated with the geomorphological setting which controls reworking by different processes such as periglacial and fluvial processes. The geomorphologic position of loess sequences is one of the key-factors controlling its role as silt sink – in both a temporal and spatial context..

¹ Lehmkuhl, F. et al. Loess landscapes of Europe – Mapping, geomorphology, and zonal differentiation. Earth-Science Reviews 215, 103496 (2021).

² Römer, W., Lehmkuhl, F. & Sirocko, F. Late Pleistocene aeolian dust provenances and wind direction changes reconstructed by heavy mineral analysis of the sediments of the Dehner dry maar (Eifel, Germany). Global and Planetary Change 147, 25–39 (2016).