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RESEARCH PRODUCT

Spatial variations in Ba/Cashell fingerprints of Glycymeris pilosa along the eastern Adriatic Sea

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Abstract The long living Glycymeris pilosa bivalve is an interesting target species for the sclerochronological research in the Mediterranean Sea. In this study, Ba/Cashell and Mg/Cashell variations were studied along the coast of the eastern Adriatic Sea. Specimens were collected alive by SCUBA and skin diving during several occasions in 2014, 2015 and 2016 from five sites including Pag, Pasman Channel, Cetina, Živogosce and Drace. Element-to-Cashell ratios were measured by LA-ICP-MS in line scan mode in three specimens of each site, ranging in age from 7 to 21. In addition, chemical analysis was conducted on three ontogenetically older specimens (68-97 years-old) from Drace. Mg/Cashell and annual growth lines were used to place the Ba/Cashell data in temporal context. Published monthly G. pilosa shell growth data were used for transferring elemental data from distance to time scale. To enable a direct comparison of Ba/Cashell data between specimens and sites (different time-averaging), as well as a comparison with environmental data, monthly mean values were calculated (re-sampling). Results of this study show that Mg/Cashell values in G. pilosa increase through lifetime and variations occur with respect to amplitude and seasonal patterns. Detailed comparison of Mg/Cashell data between sites was not possible because specimens varied in ontogenetic age. Ba/Cashell values ranged between 0.03 μmol/mol and 14.18 μmol/mol, and time-series showed noncyclic sharp peaks, which differed between years. Values were rather synchronous among specimens from the same site. Specimens from Pasman, Živogosce and Drace contain more peaks than specimens from Pag and Cetina, and these peaks are less synchronous among the time-series. Three northern sites were characterised by lower Ba/Cashell values than the two southern sites. Comparison of monthly Ba/Cashell times-series with available environmental data revealed variability of environmental conditions. Long-term Ba/Cashell data of G. pilosa from Drace showed a lower baseline and amplitude during the 1950s and 1960s than from the mid-1970s onward. It is possible that these long-term changes are at least partially caused by anthropogenic factors, including changes of the river Neretva management and development of agriculture in its delta.