Storm influence on the accumulation and lamination of sediments in deep areas of the northwestern Baltic proper

The expanding occurrence of laminated surficial sediments in the Baltic pro per has increased the possibilities to assess inter-annual variation in sed iment accumulation over the past four decades. During the same period of ti me, wind speeds and wind directions in the area have been recorded continuo usly on Gotska Sandon. When studying the fine structure in three distinctly laminated sediment cores, selected from 55 cores collected within a 39 km( 2) area, annual dry matter accumulation was found to correlate positively w ith the frequency of high wind speeds, reaching an optimum at gale force gr eater than or equal to 14 m s(-1). This confirms that resuspended sediments contribute significantly to the sediment accumulation, with a mean rate of 2 mm yr(-1) for 25 surficially laminated cores collected at depths of 115- 145 m. Decadal changes in both storm frequency and sediment deposition were observed, which may have implications not only for the turnover of sedimen ts and associated nutrients and contaminants, but also for interpretations using sediment cores as historical archives. Horizontal comparison of dated sediment layers in all cores revealed a record of substantial changes in d eep-water conditions. Recent recolonization of large areas by benthic fauna , within the depth of 102-125 m, suggests that storm events in the early 19 90s are responsible for substantially improved oxygen conditions. Although, bioturbation of laminated sediments, with a depth range of 0.5-5.5 cm in o ur samples, creates a false picture of an earlier improvement.