210pb sediment dating
In such sediment sequence, the classical application of the CRS model would provide false ages and sedimentation rates.We hypothesize that the turbidite represents terrestrial clay eroded from the Danube Delta that had been transported in pulse-like events during flash floods of the Danube River.
Correct dating of those sediments is a prerequisite for chronological reconstruction of the flux of pollutants and organic matter from the water column to the sediments and hence, the reconstruction of the pollution and eutrophication events.As the 137Cs signal is often weakened due to its mobility in sediments, 241Am, less mobile than 137Cs and derived from decay the bomb fallout of 241Pu, is used as a second time marker of the 1963 event.The northwestern shelf of the Black Sea has been seriously affected by eutrophication and pollution from the late 1960's to the mid-1990's, largely triggered by Danube River input of nutrients and pollutants.Four drops of methyl red and 1 m L of 1.8N H were added, as well as glacial acid for p H adjustment.After being centrifuged, the supernatant was taken for the analysis of lead and the precipitate was kept for radio analysis. The solution was centrifuged, the supernatant discarded and 5 m L of nitric acid (1:2) was added to the precipitate.Below the turbidite, the unsupported 210Pb and 137Cs increase again to values above the turbidite.
This points to a non-marine origin of the turbidite.
The samples were placed in a 2 L beaker and the volume was made up to 1 L with water.
To the same beaker, we added 1.0 m L (as a spike) of Pb was added so that all ions precipitate as sulphates. After that, the supernatant was separated and discarded, and the precipitate was transferred to centrifuge tubes with deionized water.
A 70 cm long and 5 cm internal-diameter wide core was used for sediment sampling.
Samples were dried at 105 °C, and about 5 g dry material was dissolved with acids.
The sediment record is repeatedly interrupted by so-called turbidites that consist of stiff clay.