Shallow water sea-floor morphologies around Asinara Island (NW Sardinia, Italy) F. Donda a,Ã , E. Gordini a , M. Rebesco a , V. Pascucci b , G. Fontolan c , P. Lazzari a , R. Mosetti a a Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/c, 34010 Sgonico, Trieste, Italy b Istituto di Scienze Geologico-Mineralogiche, Universita ` degli Studi di Sassari, Corso Angioy 10, 07100 Sassari, Italy c Dipartimento di Scienze Ambientali e Marine, Universita ` degli Studi di Trieste, Via Weiss 2, 34127 Trieste, Italy article info Article history: Received 26 April 2007 Received in revised form 27 June 2008 Accepted 3 July 2008 Available online 12 July 2008 Keywords: Northwestern Sardinia Side scan sonar High-resolution seismic Sea-floor bedforms abstract Side scan sonar, high-resolution seismic and multibeam data collected off the coast of Asinara Island in the northernmost part of Sardinia have revealed the occurrence of four distinct acoustical patterns that can be related to four main sea-bed types. The four facies represent fine sand (Type A), medium to coarse sand (Type B), patchy sand cover between basement outcrops (Type C) and a predominantly sandy sea-floor colonized by the seagrass Posidonia Oceanica (Type P). The distribution of the sea-bed types indicates that the study area is characterized by a rather complex morphological setting. A remarkable physiographic difference exists between the eastern and western sector of the island, with the latter being affected by strong, westerly winds, mainly the so-called ‘‘Mistral’’. The wave climate in this area is dominated by wind waves, which can reach a maximum height of 8 m during winter storms. Sediments are mobilized at water depths greater than 30 m from the sea surface during these energetic oceanographic regimes. We infer that dune fields and sand ribbons are deposited by strong offshore flows along the sea-bed resulting as a consequence of wave- and wind-induced onshore water transport. & 2008 Elsevier Ltd. All rights reserved. 1. Introduction The northwestern tip of Sardinia, the Asinara Island, is characterized by a remarkable physiographic difference between the western and the eastern coast: the eastern sector is character- ized by gentle bathymetric gradients, whereas the western coast is dominated by rocky coastlines with steep sea cliffs and narrow pocket beaches bounded by headlands. Here, the coast deepens sharply towards the sea and is characterized by a highly variable sea-floor morphology. During fall and winter the western coast of Asinara Island is swept by strong westerly winds that led to offshore sediment transport by strong flows along the sea-bed, allowing the formation of sea-floor bedforms of various sizes. The morphological characteristics of the sea-floor of the extreme northwestern Sardinian continental margin are poorly known. Recently, Kenyon et al. (2002) provided a comprehensive analysis of the turbidite systems on the outer continental shelf and slope off the coast of northwestern Sardinia and Corsica. However, no geophysical data were acquired in areas adjacent to the shore. The data set analyzed in the present study was acquired during three different cruises between 2000 and 2003 off northwestern Sardinia in water depths ranging from 10 to 50m. Two cruises were carried out by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) within the framework of a project aimed at monitoring water quality on the basis of the offshore distribution of the seagrass Posidonia Oceanica (Donda, 2000), which is a genus of flowering plants (Kingdom: Plantae; family: Posidoniaceae). It creates a terraced structure or ‘‘matte’’, which consists of intertwined roots and rhizomes as well as trapped sediments (Jeudy de Grissac and Boudouresque, 1985). P. Oceanica plays an important role in coastal processes because seagrass meadows filter and anchor sediments, influencing sediment dynamics in the littoral zone and contributing to water clarity and shoreline maintenance (Moriarty and Boon, 1989; De Falco et al., 2000). The third cruise was performed by the University of Sassari and focused mainly on monitoring the sea-floor between Sardinia and Asinara Island (Fig. 1), which is the location of La Pelosa Beach, that is currently undergoing erosion (Cappucci and Pascucci, 2004). The aim of this paper is to describe the sea-floor morphologies in shallow water around the Asinara Island and assess the processes that may have generated them. For this scope we complemented the morphologic data with the available informa- tion about the acoustical characteristics. We also examine the regional wind and wave regimes and then discuss the likely kind of currents that may be generated and considered responsible for the observed sedimentary features. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/csr Continental Shelf Research 0278-4343/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2008.07.003 Ã Corresponding author. Tel.: +39040 2140437; fax: +39040 327307. E-mail address: fdonda@inogs.it (F. Donda). Continental Shelf Research 28 (2008) 2550–2564