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14C dating of the biogenic littoral rims on the Adriatic islands

The biogenic (algal) littoral rims grow at around mean sea-level (MSL) and may be preserved for millennium when growing in rising sea-level environment. In order to reconstruct the relative sea-level change during the Late Holocene, algal littoral rims were collected from three islands in the Adriatic Sea, Croatia. On the particularly exposed sites on rocky coasts of islands Vis, Ravnik and Biševo these littoral rims built by the coralline rhodophyte Lithophyllum byssoides can be found. The presence of thick and well-developed Lithophyllum rims, considered to be a precise (±10 cm) sea-level indicator, points directly to the rising sea-level environment. Biogenic rims were mapped and sampled for 14C dating during 2008-2010. Two 14C methods, LSC (benzene synthesis) and AMS were used for dating algal samples. 14C activity of the calcareous deposit of a recent coralline algae, Vis Island, showed a14C of 103.7 pMC indicating that algae used CO2 from the atmosphere (mean 14C activity of atmospheric CO2 in Zagreb in 2010 was 102.0 pMC) and was also close to a14C of recent mollusks from the Adriatic sea. δ13C values of biogenic rims (2-3 ‰VPDB) indicated the marine origin, similar values were determined for the recent shells and marine biogenic overgrowth on submerged spelothems in the Adriatic Sea (Surić et al, 2005). 14C age of biogenic littoral rims from Vis Island ranged from 260 to 1490 yr BP, from Biševo Island 370 to 1440 yr BP and from Ravnik Island from 510 to 550 yr BP. The age of the obtained results are in concordance with the depth (below MSL) at which the samples of algal rims were taken. If the isostatic-eustatic component is separated, the studied area reveals almost stable tectonic conditions during the past 1500 years. Consequently the phases of sea-level changes seem to be related to the climatic variations during the same time period. The obtained results have been also compared with archaeological markers (Vis Island, Faivre et al, 2010) as well as with geomorphological sea-level markers. Faivre S, Bakran-Petricioli T, Horvatinčić N. 2010. Relative Sea-Level Change during the Late Holocene on the Island of Vis (Croatia) - Issa Harbour Archaeological Site. Geodinamica acta. 23 (5-6): 209-223. Surić M, Juračić M, Horvatinčić N, Krajcar Bronić I. 2005. Late Pleistocene - Holocene sea-level rise and the pattern of coastal karst inundation - records from submerged speleothems along the Eastern Adriatic Coast (Croatia). Marine Geology 214 (1-3): 163-175.

biogenic littorial rims; 14C dating; sea level change; Adriatic islands

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