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The Medieval Climate of the Atlantic Coast of France
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.

What was done
"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."

What was learned
Sorrel et al. report that "the late Holocene component (i.e., the last 2000 years) is best recorded in the most internal sedimentary archives," where they find that "an increase in the contribution of riverine inputs occurred during the MWP [Medieval Warm Period]" at "times of strong fluvial influences in the estuary during ca. 880-1050 AD," while noting that "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," in accordance with the findings of Proctor et al. (2000) and Meeker and Mayewski (2002). They also state that the preservation of fine-grained sediments during the Middle Ages has been reported in other coastal settings, citing the studies of Chaumillon et al. (2004) and Billeaud et al. (2005). In fact, they indicate 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 next state 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," while noting that "this shift most probably documents the transition from the MWP to the Little Ice Age," which led to the "increased storminess both in the marine and continental ecosystems (Lamb, 1979; Clarke and Rendell, 2009)" that was associated with "the formation of dune systems over a great variety of coastal environments in northern Europe: Denmark (Aagaard et al., 2007; Clemmensen et al., 2007, 2009; Matthews and Briffa, 2005), France (Meurisse et al., 2005), Netherlands (Jelgersma et al., 1995) and Scotland (Dawson et al., 2004)." And in what they call an even "wider perspective," they note that the Medieval Warm Period "is recognized as the warmest period of the last two millennia (Mayewski et al., 2004; Moberg et al., 2005)."

What it means
The French scientists ultimately concluded that "the preservation of medieval estuarine flood deposits implies that sediment reworking by marine dynamics was considerably reduced between 880 and 1050 AD," implying that during that considerably warmer period than most (if not all) of what followed it, "climatic conditions were probably mild enough to prevent coastal erosion in northwestern France." And it is important to note, in this regard, that the medieval period of exceptional warmth was caused by something other than the greenhouse effect of atmospheric CO2, since the air's CO2 content was much lower back then than it is today, which implies that the planet's present warmth may also be caused by something other than the greenhouse effect of CO2.

Aagaard, T., Orford, J. and Murray, A.S. 2007. Environmental controls on coastal dune formation: Skallingen Spit, Denmark. Geomorphology 83: 29-47.

Billeaud, I., Chaumillon, E. and Weber, N. 2005. Evidence of a major environmental change recorded in a macrotidal bay (Marennes-Oleron Bay, France) by correlation between VHR seismic profiles and cores. Geo-marine Letters 25: 1-10.

Chaumillon, E., Tessier, B., Weber, N., Tesson, M. and Bertin, X. 2004. Buried sandbodies within present-day estuaries (Atlantic coast of France) revealed by very high-resolution seismic surveys. Marine Geology 211: 189-214.

Clarke, M.L. and Rendell, H.M. 2009. The impact of North Atlantic storminess on western European coasts: a review. Quaternary International 195: 31-41.

Clemmensen, L.B., Bjornsen, M., Murray, A. and Pedersen, K. 2007. Formation of aeolian dunes on Anholt, Denmark since AD 1560: a record of deforestation and increased storminess. Sedimentary Geology 199: 171-187.

Clemmensen, L.B., Murray, A., Heinemeier, J. and de Jong, R. 2009. The evolution of Holocene coastal dune fields, Jutland, Denmark: a record of climate change over the past 5000 years. Geomorphology 105: 303-313.

Dawson, S., Smith, D.E., Jordan, J. and Dawson, A.G. 2004. Late Holocene coastal sand movements in the Outer Hebrides, NW Scotland. Marine Geology 210: 281-306.

Jelgersma, S., Stive, M.J.F. and van der Walk, L. 1995. Holocene storm surge signatures in the coastal dunes of the western Netherlands. Marine Geology 125: 95-110.

Lamb, H.H. 1979. Climatic variations and changes in the wind and ocean circulation. Quaternary Research 11: 1-20.

Matthews, J.A. and Briffa, K.R. 2005. The 'Little Ice Age': re-evaluation of an evolving concept. Geografiska Annaler 87A: 17-36.

Mayewski, P.A., Rohling, E.E., Stager, J.C., Karlen, W., Maasch, K.A., Meeker, L.D., Meyerson, E.A., Gasse, F., van Kreveld, S., Holmgren, K., Lee-Thorp, J., Rosqvist, G. Rack, F., Staubwasser, M., Schneider, R.R. and Steig, E.J. 2004. Holocene climate variability. Quaternary Research 62: 243-255.

Meeker, L.D. and Mayewski, P.A. 2002. A 1400-year high-resolution record of atmospheric circulation over the North Atlantic and Asia. The Holocene 12: 257-266.

Meurisse, M., van Vliet-Lanoe, B., Talon, B. and Recourt, P. 2005. Complexes dunaires et tourbeux holocenes du littoral du Nord de la France. Comptes Rendus Geosciences 337: 675-684.

Moberg, A., Sonechkin, K.M., Holmgren, K., Datsenko, N.M. and Karlen, W. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613-617.

Proctor, C.J., Baker, A., Barnes, W.L. and Gilmour, M.A. 2000. A thousand year speleothem record of North Atlantic climate from Scotland. Climate Dynamics 16: 815-820.

Reviewed 10 November 2010