Sediment and carbon accumulation rates off the southern coast of Finland

Abstract

The southern coast of Finland encompasses about one third of the coasts of the Gulf of Finland. It is a mosaic of hundreds if not thousands of islands, peninsulas and bays, which also are reflected in the seabed of the coast. The sea floor is composed of a patchy and fragmented mosaic of mainly quite small basins separated from each other by thresholds of islands, peninsulas or submarine ridges. This affects transport and near bottom currents such that deposition of suspended particles is restricted to certain areas only. Linear sediment accumulation rates along the southern coast of Finland were studied from 28 cores of a sampling campaign in 2000–2004 through gamma spectrometry of 137Cs. Sediment accumulation in this environment with such diverse character was found very patchy and net sedimentation rates varying from less than 0.5 cm/a to values of nearly 3 cm/a as well as mass accumulation rates from 0.5 kg/m2/a to 8.8 kg/m2/a were found. The sediment accumulation rates were observed to be higher in shallower water in coastal sheltered or semi-sheltered bays. Total carbon concentrations varied from 1.3 % to 12.6 % and carbon accumulation rates from 20 g/m2/a to 355 g/m2/a such that the highest carbon concentrations were usually found in deeper water with some distance from the coast, while the highest carbon accumulation rates were found in the coastal shallow basins where sediment accumulation was found strongest.