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Seasonal variability of the soil CO2 flux and its isotopic composition in southern Poland

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Gorczyca Z. , Rozanski K. , Kuc T. , Michalec B.

tom Vol. 48, nr 4

187-196

The flux and isotopic composition of soil CO2 has been monitored at three sites located in the southern Poland, during the time period: January 1998 - December 2000. The sites represent typical ecosystems appearing in central Europe: mixed forest, cultivated agricultural field and grassland. To monitor the flux and isotopic composition of soil CO2, the method based on the inverted cup principle was used. The flux of soil CO2 reveals distinct seasonal fluctuations, with maximum values up to ca. 20 mmolźm-2 h-1 during summer and around ten times lower values during winter. Also significant differences among the monitored sites were detected, the CO2 flux being the highest for the mixed forest site and ca. two times lower for the grassland site. The 13C content of the soil CO2 flux is nearly constant throughout the year, with d13C values essentially reflecting the isotopic composition of the soil organic matter and the vegetation type. The 18O content of the soil CO2 flux shows a remarkable seasonality, with distinctly less negative d18O values recorded during summer. This seasonality is highly reduced in the CO2 sampled from different depths of the soil. The radiocarbon content of the CO2 flux turned out to be non-distinguishable, within the uncertainty of the measurements, from current 14C levels in atmospheric carbon dioxide. However, significant reduction of the radiocarbon content was measured in the soil CO2 sampled at 80 cm, when compared to the uppermost layer, reflecting increasing age of soil organic matter with depth.

Radiocarbon dating of plant remnants in Quaternary sediments at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

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Kuc T. , Różański K. , Stachowicz-Rybka R.

tom Vol. 79, No 3

289-296

Radiocarbon dating applied on several occasions in the past to date animal bones and animal soft tissue originating from the area of the Starunia palaeontological site turned out to be very controversial. Although investigations of Pleistocene flora in the Starunia area go back to the beginning of the 20th century, no published 14C dates of such material are available to date. Sixteen boreholes drilled in the area of the Pleistocene mammals discoveries, in the framework of a multidisciplinary research project (2006-2009), have been selected for radiocarbon dating of plant macrofossils. Moreover, five samples of plant remnants extracted from two outcrops in the area were 14C-dated. The nature of the dated plant material, in some cases soaked with oil, posed specific methodological problems. Although applied chemical treatment of macrofossil samples led to complete removal of contaminating hydrocarbons in the case of small pieces, some ageing effects in terms of radiocarbon dating cannot be completely ruled out. Radiocarbon ages of macrofossil samples originating from the close neighbourhood of the location, where the "second" woolly rhinoceros was found at a depth of 12.5 m, suggest that the minimum age of sediments in which the Pleistocene mammals were found is in the range of ca. 35-40 ka BP. A broad consistency between palynological reconstruction of Younger Dryas/Preboreal boundary and the corresponding radiocarbon ages of macrofossils is observed for locations, where the natural sedimentary sequence for late Glacial and early Holocene was not disturbed by extensive mining activity in the area.