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Benthic foraminifera as proxies of the Holocene paleoenvironmental changes in the Krka River estuary (Adriatic Sea, Croatia)

Estuaries are complex and unstable coastal environments with unique organisms that evolved adjusting themselves to a specific set of conditions. Along with some rare flora and fauna, estuaries are rich in microorganisms. Often found are benthic foraminifera which are also the most common biological proxies used in Quaternary paleoenvironmental reconstructions. The Adriatic Sea has a complex late Quaternary evolution and since the Last Glacial Maximum, the sea level rise has led to the flooding of the vast coastal areas. This also led to the formation of drowned karst river valleys along the eastern Adriatic coast. Our study will focus on the Holocene paleoenvironmental record of the Krka River salt wedge estuary. The investigated environment is a unique karst estuarine setting with numerous submerged tufa barriers that influenced its Quaternary development. We analyzed in detail sediment core PROK-3, drilled by piston corer in Prokljan Lake. The foraminifera assemblages were used for paleoenvironmental assessment. The obtained data were further supplemented with additional analyses, such as radiocarbon dating, organic carbon/nitrogen analysis and grain-size. The results showed that sediments deposited during the last ~8300 years were under significant influence of sea level variability. We distinguished intervals in the basal part of the core that were barren of foraminifera, suggesting the existence of a terrestrial environment. The first evidence of marine influence is the presence of Ammonia tepida assemblages. As marine influence gradually increased due to the further sea level rise, assemblages were dominated by Haynesina sp. and Elphidium sp. and generally showed greater diversity. Our findings enabled a better understanding of the response of benthic foraminifera to sea level changes in the karst estuarine setting. The results are also important for the reconstruction of the Quaternary paleoenvironments along the eastern Adriatic coast, which is still insufficiently explored.

Prokljan Lake, Foraminifera, Holocene, paleoenvironments

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