Sedimentological investigations in a river-influenced tideless coastal embayment: The case of inner continental shelf of the NE Aegean sea

Abstract

Modern surficial sedimentology of the inner continental shelf of the NE Aegean Shelf is investigated in relation to water/sediment fluxes of the trans-boundary Evros river (draining an area of 52,900km2) and the prevailing oceanographic conditions. It also compares recent changes in the surficial sea-bed sediments with previously published data, while taking into consideration aspects of human interference and climate change. In the absence of significant tidal ranges (<10cm), nearshore wave regime and offshore circulation pattern, control the overall zonal (with respect to bathymetric contours) granulometric distribution patterns. The abundance of terrigenous material indicates the influence of Evros River despite its relatively small riverine annual suspended sediment influx (suspended to dissolved load ratio=1:8.5). The muddy belt observed in the middle shelf area is attributed to the accumulation of the riverine fine-grained suspansates and moderate hydrodynamic activity that favours nearbed transfer of fine grained material from shallower waters. The increased content in sand and biogenic material in water depths >30m, has been related to the presence of relict sands farther offshore and to the inability of Evros River to supply the outer shelf with large quantities of fine-grained sediment. Finally, the observed (although small in magnitude) changes in the offshore (>10m depth) surficial seabed sedimentology (between the years of 1986 and 2008) reflect the decreased water/sediment influxes, due to human intervention (i.e. dam construction) and climatic variations (e.g. reduced levels of precipitation). Hence is a progressive change of offshore sediments towards a more biogenic composition, is expected.