Physico-Chemical Features and Subsurface Nature of Coastal Dunes on Bozcaada Island, NW Turkey

We studied the composition, vegetation cover, wind regime characteristics and subsurface nature of a coastal dune field on the west coast of Bozcaada Island, NW Turkey. Performing Electrical Resistivity Tomography (ERT) technique, we determined that dune sands with a thickness of ~11-13 m cover the underlying Miocene basement, as confirmed by an abrupt increase in resistivity as from lithological boundary. The results demonstrate that foredune terraces and ridges differ from swales from various points of view. The foredune sands are characterized by average contents of over 82% medium to fine-sized angular sands, especially quartz (85%), based on X-ray fluorescence spectroscopy (XRF) data, CaCO3 (1.15%) and organic matter (0.19%). On the other hand, swales are composed on average of 59% medium to fine sands, a mixture of silt and clay (13%), very coarse sands and small-size gravels (28%). In addition to the different grain size distribution, swale sediments have conspicuously lesser amounts of SiO2 (78%), higher amounts of CaCO3 (5.6%) and organic matter (0.8%). Wind climatology analysis showed the predominance of a northerly (mainly NNE) near surface wind circulation over Bozcaada throughout the year with high wind speeds of maximum 7.4 m/s. Nevertheless, the existing sand transport and associated development of foredune forms and blowouts in the dune field relates considerably to the bimodal distribution of northerly winds (NNW and NNE). Although the coastal dune area is capped by a variety of dune plants, blowout development is highly active, in particular, on the northeast section of the dune field.