Impact of katabatic winds on the environment of Neanderthals during the Middle Palaeolithic in westernmost Europe

Abstract

Compilation of the offshore and onshore altitudinal limits of the loess deposits of western France and southern England shows that they were deposited by low-level wind fields. These relate to (i) the deflation of silt-rich sediment extracted from the outwash plains of the not far distant British-Irish Ice Sheet and from the palaeo-rivers of the Channel, and (ii) the existence of north and north-western palaeo-winds deduced from particle size analysis and heavy mineral distribution, and suggest (iii) that loess particles were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. Comparison between the main orientation of Neanderthal shelters and the direction of the katabatic winds shows that they were perpendicular to each other. The dominant orientation of the shelters was apparently ruled by these winds. A small-scale study concentrating on the penultimate glaciation shows that in contrast to Brittany and Normandy where loess deposits accumulated on northfacing cliffs, in England the same particles were deposited on the leeside of the hills. The existence of deflation zones, violently swept by Marine Isotope Stage 6 katabatic winds south of the British-Irish ice sheet, was probably at the origin of the restricted number of Neanderthals at that time in England.

Transit boosting of trans-Channel katabatic winds by depressions associated with the west European storms tracks: impact on Pleistocene loess deposits

“…-If we incorporate the results of the different studies dedicated to the heavy and flaky minerals in England and Brittany (Lefort et al, 2019) we can estimate that the maximum distance reached by the katabatic winds is close to 750 km, which is in the range of the distances observed by Bromwich et al, (1992). However, the distance reached by the katabatic winds above the sea cannot be fully compared with the distance of propagation measured between the top of the English-Irish ice sheet (Boulton and Hagdorn, 2006) and the mouth of the Loire river where a very limited migration of augite (the southernmost heavy mineral marker) can be still observed (Lefort et al, 2019;2021), since the north-south corridor funnelling the katabatic winds is not completely flat like the sea but affected by small topographic rugosities (Figure 2).…”

“…-All the available data collected in Brittany and Normandy indicate a British or Channel origin for the winds blowing from the North and Northwest (Lautridou, 1970;1985;Antoine et al, 2003;Lefort et al 2019;Lefort et al, 2021) (Figure 1). It is certain that the wind directions based on the heavy minerals are not very accurate since the sources of these particles are often spread over a large longitudinal distance.…”

“…It is certain that the wind directions based on the heavy minerals are not very accurate since the sources of these particles are often spread over a large longitudinal distance. By contrast, the orientation of the cliffs which collected the aeolian dust provides (Lefort et al, 2019) more accurate wind directions since the south, west and east facing cliffs are generally free of important loess thicknesses (Lefort et al 2021). The more useful criterion for the determination of the wind direction is certainly that of granulometric study (Bigot, 1986).…”

“…In the south of England (except in the SW Peninsula), katabatic winds were able to override the southern English Hills characterized by an approximate difference of less than hundred metres respect with the outwash plain. Because the strength of the katabatic winds was decreasing in a southward direction, loess was deposited on the lee side of the hills in southern England and on the windward side in northern Brittany (Lefort et al, 2021).…”

Depositional conditions of the Upper Younger Loess during the Last Glacial Maximum in central and eastern Europe

“…This resulted in major environmental changes in the areas adjacent to the ice sheet and changes in vegetation further on its foreland (Granoszewski 2003;Mamakowa 2003;Gerasimenko and Rousseau 2008;Komar et al 2009;Łanczont et al 2021). The LGM climate variations are confirmed in the lake cores (Dzierżek and Szymanek 2013;Kalińska-Nartisa et al 2016) and glacial sediments (Dzierżek and Stańczuk 2006;Marks et al 2019) as well as in loess profiles (e.g., Jary 2007;Jary and Ciszek 2013;Jary et al 2021;Łanczont and Boguckyj 2007;Antoine 2009b;Sima et al 2009Sima et al , 2013Marković et al 2009;Bokhorst et al 2011;Lefort et al 2021;Rousseau et al 2021).…”