Spatial variability of recent sedimentation rates in the Eastern Gotland Basin (Baltic Sea)

In order to study recent sedimentation rates in the Eastern Gotland Basin, 52 short sediment cores collected from the deepest part (< 150 m) of the Basin in 2003 were investigated. The upper parts of all the cores were distinctly laminated and dark in colour, followed by a homogeneous, greyish lower part. The thickness of the laminated sequences varied from 17 to 300 mm. Pb-210 dating analyses of selected cores revealed that the change from non-laminated to laminated sediments happened about 100 years ago, indicating a shift from predominantly oxic bottom water conditions to anoxic conditions. Used as a time marker, this shift in the sediment texture enabled sediment accumulation rates to be estimated for all sediment cores. The observed mean linear sedimentation rate for the whole basin was 0.93 +/- 0.67 mm yr(-1). The respective bulk sediment accumulation rates ranged from 10.5 to 527 g m(-2) yr(-1) with an average of 129 +/- 112 g m(-2) yr(-1), indicating a high spatial variability of sedimentation rates within the basin. This agrees very well with the long-term sedimentation pattern since the Litorina transgression. The observed pattern clearly reflects the hydrographic conditions at the seafloor as studied by modelled near-bottom current velocities.