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

International audience ; Onshore and offshore sedimentological, geochemical, geomorphological, palaeontological and geochronological studies of loess deposits located under and around the English Channel revealed that they were transported by katabatic winds generated by the British-Irish Ice Sheet. Katabatic winds, which are low-altitude wind flows, were able to jump over the low southern British hills but were stopped by the higher Brittany and Normandy hills. This regional topography is interrupted by a north-south corridor linking the northern and southern shores of Brittany where loess propagated down to the mouth of the Loire River. This long transit shows that the total distance travelled by the katabatic wind was around 750 km, which represents an unusual distance for the propagation of this wind under continental conditions. Strong similarities with Antarctica and Greenland, where well documented cases of katabatic winds are known, show that the transit of the trans-Channel katabatic winds were strongly enhanced by the seasonal drift of storms propagating in an eastward direction along the axis of the English Channel. This increasing strength of the north-south katabatic flux was probably at the origin of the transport of loess particles down to the mouth of the Loire River.