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Pleistocene and Holocene environmental changes in the eastern part of the mid Adriatic deep influenced by sea-level rise and shoreline retreat

During a 21-day long cruise onboard the RV Poseidon in the year 2017., a multinational team of scientists collected water and sediment samples in the Adriatic Sea. The cruise POS514 entitled „Micropaleontology, Actuopaleontology, and Environmental Baseline Study of the Holocene to latest Pleistocene in the northern and eastern Adriatic Sea basin“ comprised scientists from German, Italian, Croatian, and Austrian institutions. Scientists measured water column properties with CTD probe, collected biological samples with plankton multi net, and collected sediments with long gravity cores, short multi- cores, Van Veen grabs, Box cores, and Frahm corer on 40 sampling stations (Figure 1a). The gravity core POS514-40-11 GC was collected along the Eastern Adriatic Coast in the northern rim of the Mid Adriatic Pit (Figure 1a) at a water depth of 212.5 m b.s.l. Its total length is 690 cm. The core is of special interest due to the focus of the Croatian Science Foundation project QMAD, with extensive studies in the area of the Krka River estuary and its development towards the MAD during the Pleistocene and Holocene eustatic sea-level fluctuations. The dating of the core was established with five dates using the AMS 14C method, calibrated with the IntCal20 calibration curve in the Clam software (Blaauw, 2010). The oldest date reached 17 900 cal BP at the core depth of 628 cm. The dates were used to create the age-depth model and calculate sedimentation rates (SR) in the MAD (Figure 1b). The peaks of the measured 137Cs activity were not completely conclusive. Other methods used for the core determination include measurements of the particle size (PSA), magnetic susceptibility (MS), carbon and nitrogen (Total C, Total N, C/N ratio, Total Organic Carbon (TOC%), Total Inorganic Carbon (TIC%)), bulk density (BD) (wet and dry), mineralogical (XRD) and derived values as Mass Accumulation Rates (MAR) and Accumulation Rates of C, N, TOC%, and TIC% (Figure 1c). A distinct change in SR, BD, as well as in MAR that starts from 9 440 cal BP to 12 100 cal BP and remains high until the end of the core. Values of the TOC% show the opposite pattern. There is a sudden rise in TIC % and MS at the lower part of the core, at 15 150 cal BP, coincident with a PSA peak of sand particles (Figure 1c). In general, sediments of the whole core are dominantly silty with 20% to 30% of clay-sized particles, with two short sand intervals. The other peak of sand particles occurs at 8 800 cal BP and can also be observed in MAR and TIC%. The C/N ratio is uniform in a range of 7 to 8, with one distinct peak at 13 000 cal BP reaching 9.8. Based on XRD analyses the main difference throughout the core is the amount of two dominant minerals – quartz and calcite. Within the top 2.7 meters (9 700 cal BP) of the core, the amount of the calcite is higher than the quartz, while in the part from the third to the fifth meter (14 700 cal BP) the amount of the quartz is higher. From the fifth meter to the bottom the amount of calcite is again higher than the amount of quartz. This coincides with changes in the other parameters measured within the core (MS, TIC MAR) (Fig 1a). Collected data enabled us to define four distinct zones throughout the core (Figure 1c). The zone POS Z1 extends from the bottom of the core until 15 150 cal BP. It is followed by the POS Z2 zone with a transition to the third zone (POS Z3) at 12 090 cal BP. The youngest and the longest zone POS Z4 extends from the 9 440 cal BP to the surface. Zones Z1 and Z2 deposited in the environment proximal to the coastline, with more pronounced terrestrial and coastal influence on the sedimentation. Zone Z3 represents gradual coastal retreat further from the location due to sea-level rise, with diminishing coastal effect. The youngest zone Z1 was sedimented in the deeper water distal environment that lasts until the present. The obtained results will be extremely helpful in the interpretation of high-resolution acoustic profiling that is planned for the next project period.

marine sediments ; mid Adriatic deep ; total organic carbon ; paleoenvironment

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