engleski

A multiproxy analysis of Holocene lake sediments on the Eastern Adriatic coast

Croatian karst region on the Eastern Adriatic coast is characterised by karstic features that lack permanent water bodies, like lakes. Their occurrence is valuable source for paleoenvironmental research using undisturbed sediment cores. Holocene climate dynamics lack of well resolved and dated records in the Eastern Adriatic. Along the coast, from north to south, during the past few years, we have recovered more than 50 m of sediment cores that needed exact chronological time frame. Sediment cores were dated using radiocarbon absolute dating of shells, charcoals or plants, deposited in the sediments. Lake sediments were studied using multidisciplinary approach, combining sedimentological, mineralogical and geochemical analysis with paleontological proxies like pollen, ostracods or diatoms. The most of the lakes cover the end of Pleistocene and beginning of the Holocene and show the evolution of the lakes and environmental changes during the last 12.000 years. Paleolimnological research was conducted on Lake Vrana on the Island Cres, Bokanjačko blato, Lake Vrana near Biograd and Lake Baćina- Crniševo. Lakes represent typical karst lakes dominated by carbonate sedimentation, with periodic siliciclastic input. Due to the proximity of the sea and permeable karst, the lake levels are influenced significantly by the sea level rise during the Holocene. Deposition of the siliciclastic material in Lake Vrana near Biograd lasted until 9.1 ka BP, when carbonate lake sedimentation started and the lake was formed. The marine influence on the Lake Vrana sediments is visible after 6.1 ka BP, and additionally, gradually increase of siliciclastic components is a result of deforestation, which allowed increased soil erosion and input to the lake. At 3 ka BP started the deposition of the carbonate mud. In Lake Baćina deposition of the siliciclastic material was very intense from 11.7 to 10 ka BP, and then gradually decline until 7.5 ka BP. Dominant carbonate deposition lasted from 7.5 until 4.5 ka BP, when intensive changes in the sediments began, observed by the high sand fraction until 2.5 ka BP, and in between the alternate intervals were developed with calcite and quartz and those in which only calcite is present. From that time (4.5 ka BP) the slow increasing of the siliciclastic material were observed, indicating the increasing human impact and deforestation. In Bokanjačko blato the deposition of siliciclastic material lasted from 10.3 to 6.1 ka BP and then gradually decreases until 5.2 ka BP, when carbonate deposition began. In Lake Vrana on the Island Cres, the beginning of the Holocene is characterized by the deposition of the siliciclastic material, but which continues to the middle Holocene, until 4.5 ka BP when the carbonates appear. During the Holocene contrasting climate pattern has been identified in the central Mediterranean: north of around 40°N of latitude was characterised by a wetter early Holocene, followed by relatively drier conditions during the middle Holocene and gradually increased moisture in the Late Holocene, while south of 40°N there is opposite trend, very dry conditions in the first half of the Holocene and wettest period during the Mid Holocene followed by a progressive aridification. Investigated lakes on the Eastern Adriatic correlate well with the lakes situated above 40°N. The work presents four paleoenvironmental lake reconstructions that show evidence for Holocene climate changes associated with Mediterranean climate dynamics and Adriatic Sea level changes.

Holocene; lake sediments; multiproxy analysis; environmental changes

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