Subaqueous bedforms on the Cyclades Plateau (NE Mediterranean) — evidence of Cretan Deep Water Formation?

Abstract

Sandy bedforms are surveyed on the northern–northeastern Cyclades Plateau using side-scan sonar and 3.5 kHz continuous subbottom profiling system. The bedforms appear in water depths of 80–130 m, as; (a) dunes (3-D megaripples; wavelength 10–35 m and height 1–2 m), composed of moderately well-sorted coarse sand; (b) large to very large sand waves (wavelength 50–300 m and height 1.5–6 m) developed usually in fine-medium sand; (c) 2-D megaripples (wavelength 3–5 m and height 0.2–0.4 m); (d) narrow sand ribbons (thin erosional lineations); and (e) elongate sand patches, together with those of different configurations. The presence of these bedforms implies strong near-bed flow, of the order of 40–100 cm/s; and, locally, in the case of sand ribbons, up to 200 cm/s. Short-period (15 day) deployments of near-bed current meters did not observe such values; maximum and mean velocities were 10–15 and 6–7 cm/s, respectively. Indirect evidence, provided by the local fishermen, is indicative of strong currents. Dense water mass formation, during cold winters, is considered to be responsible for the development of these bedforms. During seasonal cooling, such waters sink rapidly and flow towards the south, flooding the deeper part of Cretan Basin (Cretan Deep Water (CDW) formation); they overflow the Cretan Straits and are dispersed into the Eastern Mediterranean. Sites for this formation of CDW are considered to be the Cyclades Plateau and possibly the North and the Central Aegean Sea.