Radiochronology of sediments from the Mediterranean Sea using natural210Pb and fallout137Cs

Abstract

The 210pb and 137Cs profiles of sediment cores from two locations in southem Spain, three locations in southern Turkey and two locations in n0rthem Cyprus were determined by direct ~/-ray spectroscopy. Sedimentation rates were derived for all locations using the 210pb data. The rates range from 1.39 + 0.12 cm. y-1 (0.50 + 0.04 g. cm -2-y-l)to 0.08 + 0.01 cm-y-1 (0.039 + 0.003 g. cm -2. y-l), Except for one core, the 137Cs profiles were also used to compute sedimentation rates. Accurate dating techniques are important in the use of sediment records for reconstruction of recent environmental changes, The precision to which this can be accomplished has been greatly enhanced ever the past 20 years by the development of a range of radiometric techniques that use radioisotopes both from natural and artificial sources. The principal isotope for dating in the time scale of the past 100-150 years is 21~ 21~ with a half-life of 22.6 years is a member of the natural 23su series. Using this itosope, lake and sea sediment can be dated with a precision of five to ten years. In this method the activity of the unsupported 21~ (i.e.. total activity of 21~ in the sediment minus that supported by 226Ra) is measured throughout the sediments. Artificial radioisotopes such as 137Cs have been present in the environment only for the past 35 years, and can be used for dating only the most recent sediments. 137Cs is produced during nuclear fission. Thus, its presence in the environment is due to nuclear testing or to releases from nuclear reactors. In these tests, 137Cs was injected into the stratosphere where it circulates globally. 137Cs moves from the stratosphere back to the troposphere and it is precipitated from the troposphere to the earth's surface. The use of this isotope does however provide a valuable check on the accuracy of the 21~ data. Most of the researchers measure the unsupported 21~ by measuring the a-emission of 21~ or by measuring the [3-emission of 21~ Although these melhods are highly sensitive, they are very complex and require radiochemical separation techniques. With the development of hyperpure germanium detectors, it is possible to measure 21~ in

Approaches to unravel seasonality in sea surface temperatures using paired single-specimen foraminiferalδ18O and Mg/Ca analyses

“…Subsequently, bioturbation increases the time interval captured in an individual sample, which also enhances the variability present in the sample. If we use the sedimentation rates at nearby locations of 10–30 cm/kyr [ Rupke et al , 1974, and references therein; Tadjiki and Erten , 1994; Rutten et al , 2000] as a guideline, the core top samples used in this study encompass 70–200 years. Lower sedimentation rates would result in a longer time period covered in individual samples.…”

Radiochronological Methods as Tools to Study Environmental Pollution

“…The radionuclide 210 Pb (t 1/2 = 22.3 y), a member of the natural radioactive decay series of 238 U, provide a reliable possibility of dating sediments over the last 200 years [1]. This technique has since seen further refined and very widely used by many researchers [2][3][4][5][6][7][8][9][10][11]. This method of dating, requires the complete recovery of the topmost sediment layers.…”

“…We have used the above mentioned radioisotopic methods over the years for the dating of sediments from Lakes Zurich and Constance, the sea of Marmara, southern Turkey, eastern Spain, the Black Sea region and northern Cyprus [5][6][7][8][9][10][11].…”