Evidence of benthic colonisation during formation of laminated sediments in the Gotland Deep, Baltic Sea

Benthic foraminifera were found in laminated non-bioturbated sediments from the Gotland Deep in the Baltic Sea. The sediments were deposited during th e Littorina Sea stage (8000-3000 C-14 yr. BP), where euxinic conditions (an oxic bottom water) prevailed in the deepest part of the basin. The bottom w ater became occasionally oxygenated when saline oxic water entered the basi n. During some of the oxic periods, a benthic oxygen-demanding fauna was ab le to colonise. The oxygen levels below the sediment-water interface were, however, too low to admit a burrowing fauna. The foraminifera were protecte d from upward diffusing H2S by a layer of manganese oxide acting as a redox buffer. It is concluded that colonisation of benthic foraminifera occurred during short periods suggesting that an establishment could take place if the deep bottoms of the present-day Baltic Sea became oxic.