Doc from AMP_Sinis, 4 years, 11 months ago
Inputs of biogenic carbonate sediment from Posidonia oceanica seagrass meadows to four beaches of the Sinis peninsula (Sardinia, western Mediterranean) were evaluated.Beach and continental shelf sediment samples were analysed for grain size distribution and composition, biogenic vs. siliciclastic, in order to identify the provenance of beach sediments and sediment transport pathways. Seabed mapping was carried out in order to identify the distribution of meadows and sediment deposits oﬀshore. Shelf sediments were collected in unvegetated sites and in P. oceanica meadows. Sediments from unvegetated sites were coarse sands and gravel, mainly siliciclastic (biogenic carbonate content is 3–7%). Sediments from P. oceanica meadows were coarse sand, mainly biogenic (carbonate contents varying between 60 and 90%). Beach sediments showed bimodal grain size distribution (59% of samples) resulting from mixing of coarser siliciclastic with ﬁner biogenic materials in variable proportions. Biogenic carbonate contents in beach sediments range from 0 to 90%, reaching the highest values in oﬀshore samples. Analysis of grain size and compositional trends from shelf to beach sediments highlighted that the latter originate from two diﬀerent sources: erosion of granitic outcrops, providing the siliciclastic component, and export of sediments from P. oceanica meadows, providing biogenic material. P. oceanica meadows also inﬂuence shore by contributing towards maintaining the beach sediment budget.