0 m and a slope gradient of 4° (Figure 14 – Profiles 03 and 04). All the furrows formed by trailer suction dredging had disappeared completely after 11 months (Figure 14 – Profiles 05, 06, 07) except for one depression 70–80 m in diameter and with a maximum depth of 0.5 m left by the deepest pair of furrows, initially

1.9 m deep. The increasing scale of offshore dredging is raising questions not only HSP inhibition about the impact of these activities on the marine environment, but also about the availability of sand and gravel resources. There is a scarcity of sediments in many regions of the Baltic Sea owing to the low input of material. Therefore, information on the age and origin of the sand and gravel deposits as well as about their BIBW2992 ic50 stability and potential for regeneration are of great importance. Considering the age of the layer of marine sand under

discussion and taking into account the rsl curve for the southern Baltic (UŚCINOWICZ 2003, 2006), we can state that the transgressing sea reached the area of investigation ca 8500 years ago. The radiocarbon age of marine shells (3275–3145 and 4775–4590 cal. y. BP) and the significant admixtures of gravel in the lowermost part of the bed of sand indicate that erosion and redeposition predominated during ca 5000–4000 years, and that when transgression ceased and the sea level approached the contemporary one, the accumulation of sand started. During the following ca 3500–4500 years, a 2–4 m layer of marine sand accumulated; it would seem that at that time

redeposition during storms probably did not reach the floor of the layer. The thickness of the contemporarily mobile layer of sand, as determined by measurements of the 137Cs content in the cores, is between ca 0.40 m in core COST-8 and ca 0.8 m in core COST-3 (Figure 7). A similar thickness of sands containing radiocaesium (0.4–0.6 m) was shown by investigations carried out 15–20 km to south-east of the test area at 15–20 m depth (Łęczyński 2009). The depth of radiocaesium penetration depends not only on near-bottom hydrodynamics but also on the grain size distribution of sediments. The water depth at the sites where cores COST-3 and COST-8 were taken is nearly the same: 15.1 m and 15.6 m respectively. Farnesyltransferase This halfmetre difference in water depth does not justify the difference in the depth of 137Cs penetration into the deposits. This is most probably due to the dissimilarity in grain sizes. Coarse sand with an admixture of gravel is present in the area from which core COST-8 was taken, whereas medium sand overlies the area where core COST-3 was obtained. Medium sand needs a lower critical current velocity to initiate its movement than coarse sand, and storms can rework a thicker layer of the deposit. Other basic questions concern the rate of regeneration, i.e. the rate of disappearance of morphological changes and changes in sediment distribution.