Sediment lithology and stable isotope composition of organic matter in a core from a cirque in the Krkonoše Mountains, Czech Republic

This study presents detailed lithostratigraphy and stable carbon and nitrogen isotopic variations in a 520-cm-long sediment core from a cirque basin in the Labský důl Valley, Krkonoše Mountains, Czech Republic. Detailed study of the core reveals five major periods of sedimentation during the last 7600 years: silt and sand deposition during ~7.6-5.1 ka cal BP, Sphagnum peat accumulation during ~5.1-4.0 ka cal BP, sandy silt and sand during ~4.0-2.8 ka cal BP, raised peat bog during ~2.8-2.0 ka cal BP (Sphagnum peat), and sedimentation of sandy silt since ~2.0 ka cal BP. The δ13C values of the organic matter in the core vary in the range typical for C3 plants, from -24.35 to -27.68‰, whereas the δ15N values vary from -2.65 to +4.35‰. Core sections having ash contents ≥70% have δ15N > 1‰ and δ13C < -26‰, whereas those having ≤70% ash content have δ15N < 1‰ and δ13C > -26‰. Strong linear correlations are observed between δ13C and δ15N values as well as between C:N ratios and δ15N values in the horizons with ash content >10%, primarily for sand and silt horizons. On the other hand, poor correlations between δ13C and C:N ratio, as well as δ15N and C:N ratio, were observed in Sphagnum peat layers (45-125 and 185-265 cm). We conclude that the primary stable isotope variations are not preserved in the layers where significant correlation between δ15N and C:N ratio is observed. The relatively small δ13C variation in the uppermost Sphagnum peat layer suggests stable temperature during ~2.8-2.0 ka cal BP.