The central Baltic Sea/Gotland Basin: Age model, physical properties, geochemical and isotopic data of kasten core KaL#20048-1, gravity core SL#20048-4 and multicore MUC#20007-1

Title: Results of physical properties, elemental analysis and stable isotope investigations of cores (kasten core and multicore) from the central Baltic Sea (Gotland Basin).

Coring and sample processing: A 10.30 m long kasten core (KaL#20048-1) and a 10.40 m long gravity core (SL#20048-4) were recovered (57°23.14'N, 020°15.51'E; water depth 241 m) by r/v Poseidon and a multicore (MUC#20007-1) at the same position by r/v Alexander von Humboldt in 1994 (expedition 94.44.13.2). The kasten core was opened and logged on board, and 10 cc samples for determinations of physical properties, elemental and isotope analyses were taken with graduated plastic cylinders (syringes with sawn-off tops) punched into the cleaned core face. The syringes were sealed by end caps, taped and frozen until shorebased analyses. The entire kasten core was archived in plastic boxes. The gravity core (SL #20048-4) was cut into 1-m sections, capped and stored. The multicore #20007-1 was sliced into 1-cm slices which were frozen immediately after core retrieval.

Age model: The age model of kasten core #20048-1 and multicore 20007-1 is based on 12 accelerator mass spectrometry (AMS) 14C age determinations performed at the Leibniz Labor für Altersbestimmung und Isotopenforschung at Christian-Albrechts-Universität zu Kiel/Germany. Twelve samples were from the kasten core and 2 from the multicore. Two 14C ages from the lowermost core section of the kasten core were not used for the age model, because they yielded ages that were too old. Instead, the age model in the lowermost core sequence relies on three lithological markers: Termination of Yoldia stage, final drainage of the Baltic Ice Lake, and first drainage of the Baltic Ice Lake. Two samples for 14C dating of the multicore were chosen from intervals that are older than 1950 CE based on 210Pb ages. Comparison of weight % total organic carbon (TOC) and delta 13C-values of kasten core and multicore showed that the top 10.5 cm of the kasten core were lost during recovery, because the surface sediment in the Gotland Basin is soupy. Sample depths in the kasten core have thus been adjusted for this loss (adjusted depth denoted as xxx cm adj.). All 14C ages were converted to calendar ages using the marine data set of the INTCAL98 radiocarbon calibration curve (Stuiver et al., 1998) and the Oxcal 3.5 software. Gravity core #20048-4 was correlated to kasten core 20048-1 from the same location by physical properties and visual inspection and the age model for the kasten core was applied to the gravity core after correction for over-penetration.

Physical properties, elemental and isotope analysis: Syringe samples and MUC slices were weighed, freeze dried, and weighed again in the shorebased laboratory to determine water content and dry-bulk density. Subsamples were then homogenised by mortar and pestle for further analyses. Approximately 20 mg of the homogenized sample was weighed into tared silver-foil sample vessels for elemental composition (total carbon, total nitrogen, organic carbon) and isotope analyses (delta15N, delta13C of organic carbon). Total carbon, total nitrogen and delta15N (in permil versus Air N2) were determined simultaneously in a Carlo Erba/Fisons 1108 Elemental Analyzer connected to an isotope-ratio mass spectrometer (Finnigan Delta S) after combustion. A second sample split was treated with 2N HCl to remove inorganic carbon. On this sub-sample, the concentrations of TOC and isotope ratio delta13C of organic carbon (given in permil versus V-PDB) were determined simultaneously in a Carlo Erba/Fisons 1108 Elemental Analyzer connected to an isotope-ratio mass spectrometer (Finnigan Delta S). The reference gas was pure CO2 from a cylinder calibrated against carbonate (NBS- 18, 19, 20). The standard deviation for replicate analyses of delta13C was less than 0.2 permil.