A Diary Written in Dust
In an unassuming corner of northern Bavaria, exposed in a former brickyard quarry near the town of Unterhaid, lies a remarkable natural archive. This is one of the important loess sections studied by geologist Wolfgang Soergel, a thick deposit of wind-blown dust that chronicles the dramatic climate shifts of the Pleistocene epoch. Loess is a sediment formed by the accumulation of silt-sized particles, ground down by continental ice sheets and transported by wind across the periglacial landscapes that sat south of the ice. In southern Germany, the primary source for this dust was the vast floodplains of rivers like the Danube, which carried sediment from the glaciated Alps.
These deposits are a layered climate diary. During cold, dry glacial periods, strong winds picked up immense quantities of fine dust from barren riverbeds and deposited it across the landscape, forming thick, yellowish layers of loess. When the climate warmed during interglacial periods, vegetation returned, and the loess deposition slowed or stopped. This allowed for the formation of dark, humus-rich soils, called paleosols, directly on top of the previous loess layer. This cycle of dust accumulation followed by soil formation repeated with each ice age, creating a distinct sequence of alternating light and dark bands that geologists can read.
Reading the Layers
The loess-paleosol sequences in central Europe are one of the most important terrestrial records of Quaternary climate change. The section near Unterhaid, like others in the region, preserves evidence of multiple glacial-interglacial cycles. By analyzing the physical and chemical properties of each layer, scientists can reconstruct past environmental conditions in considerable detail. The thickness and grain size of the loess layers show wind strength and proximity to the dust source.
The dark paleosols are especially informative. Their structure, chemistry, and organic content indicate the type of vegetation that grew and the climate that prevailed during warm interglacial periods. Some of the most well-studied layers correspond to the Eemian interglacial (around 126,000 to 115,000 years ago), the warm period just before the last ice age. These ancient soils show that central Europe was covered by deciduous forests under conditions similar to or even warmer than today.
Embedded within these layers are also microscopic fossils, particularly the shells of terrestrial snails (mollusks). The specific species found are excellent climate proxies. Cold-resistant, open-habitat species dominate the loess layers, while species that prefer warmer, more forested environments are found in the paleosols. This faunal evidence provides an independent proof of the climate oscillations recorded in the sediments themselves.