LAUSR

Purpose: Measurement of carbon in cores of undisturbed sediments may provide valuable information on historical trends in sea primary production and carbonate precipitation which can be related to climate changes. Since core sediments are usually subjected to a different analysis, it is important to preserve the sample. A non-destructive technique for carbon measurement in sediments based on fast neutron activation analysis (FNAA) has been developed, which might replace the loss-on-ignition (LOI) as a conventional method for carbon analysis. Materials and methods: The method was tested on sediment samples collected from the Western Black Sea at depths up to 22 m. A surface sample and a core cut in centimeter intervals were freeze-dried. Samples weighing between 60 and 300 g were irradiated with the portable neutron generator. Gamma rays from 12 C(n,n'γ) 12 C nuclear reaction were counted between 2000 and 4000 s by LaBr 3 :Ce detector. Standards for direct comparison and construction of the calibration line were prepared as mixtures of different amounts of quartz sand and graphite powder. The FNAA results for total carbon (TC) were verified by LOI at 1000 °C. LOI at 450 °C and treatment with 1 M HCl were used to separate inorganic carbon (IC) and organic carbon (OC), respectively, followed by the FNAA measurements. Results and discussion: Climate effects on physical and biological marine processes are evident as historical changes in carbon flux to sediments. Carbon in sediments is found in the form of the OC produced by photosynthetic organisms and as IC produced by calcifying organisms and precipitated as calcite. The FNAA is usually applied to samples weighing more than 1 kg. The method was optimized to reduce the minimum weight of the sample to 60 g, after subsequent adaptation of the setup geometry. Carbon content measured in cores and surface sediment was between 2.8 and 6.1 wt%. OC constituted up to 84% of TC measured in the core. The FNAA measurements were in good agreement with LOI analysis. Conclusions: The results have shown that FNAA can be used for the non-destructive determination of carbon in sediments in samples weighing ≥ 60 g. FNAA is non-destructive, robust, and fast in comparison to conventional methods for carbon determination such as LOI. The disadvantage is a relatively high MDL of 1%.