Sorrel, P., Tessier, B., Demory, F., Baltzer, A., Bouaouina, F., Proust, J.-N., Menier, D. and Traini, C. 2010. Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine, south Brittany): Depositional history and late Holocene climatic and environmental signals. Continental Shelf Research 30: 1250-1266.
"Based on an approach combining AMS 14C [radiocarbon] dating, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine [47°20'-47°35'N, 2°50'-2°30'W]," the authors documented, as they describe it, "the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany." This work indicated that "an increase in the contribution of riverine inputs occurred during the Medieval Warm Period" at "times of strong fluvial influences in the estuary during ca. 880-1050 AD," and they say that this "preservation of medieval estuarine flood deposits implies that sediment remobilization by swells considerably waned at that time, and thus that the influence of winter storminess was minimal." They also state that the preservation of fine-grained sediments during the Middle Ages has been reported in other coastal settings and that "all sedimentary records from the French and Spanish Atlantic coasts" suggest that "the MWP appears to correspond to a period of marked and recurrent increases in soil erosion with enhanced transport of suspended matter to the shelf as a result of a likely accelerated human land-use development," adding that "milder climatic conditions during ca. 880-1050 AD may have favored the preservation of estuarine flood deposits in estuarine sediments through a waning of winter storminess, and, thus, reduced coastal hydrodynamics at subtidal depths."
The eight researchers also found that the upper successions of the sediment cores "mark the return to more energetic conditions in the Bay of Vilaine, with coarse sands and shelly sediments sealing the medieval clay intervals," and they say that "this shift most probably documents the transition from the MWP to the Little Ice Age," which led to the "increased storminess" in marine and continental ecosystems that was associated with "the formation of dune systems over a great variety of coastal environments in northern Europe," including Denmark, France, the Netherlands and Scotland." And in what they call an even "wider perspective," they note that the Medieval Warm Period has been "recognized as the warmest period of the last two millennia." Thus, we have reason to recognize the MWP in the vicinity of the Bay of Vilaine as prevailing from about AD 880-1050.