RECONSTRUCTION OF LITTLE ICE AGE PALEOWIND DIRECTIONS FROM COASTAL SAND DUNES IN VIANA DO CASTELO, NW PORTUGAL

In this study, coastal sand dune complexes along the Atlantic northwestern coast of Portugal, in southwest Europe, are used to better understand changes in paleowind and paleoclimatic conditions since the Little Ice Age (LIA). Specifically, we investigated a massive 6 km long LIA coastal sand dune complex in Viana do Castelo near the mouth of the Lima River for detailed grain size analysis, paleowind direction, and Quaternary geochronology.

Grain size analysis results from four different dunes within the complex displaying planar cross bedding revealed unimodal distributions that consist of well sorted medium quartz sand (average graphic mean of 1.32 phi). Paleowind measurements from the same planar cross bedding units show orientation values ranging from 290o to 357o with an average of 334o, suggesting genesis of the dune complex is due to a prevailing wind direction essentially from the NNW, with a range of winds blowing from between the WNW and the N.

We interpret the prevailing LIA NNW wind responsible for the genesis of the complex to be associated with an increase in the number of cold fronts (related to the Icelandic Low) mainly during the winter months. The presence of strong summer sea breezes blowing from the NNW known locally as “Nortadas” must have also contributed to the genesis of the dune complex. Sand collected from the dune complex for IRSL dating will reveal the timing of its genesis.