Search

We present a study on the use of 239,240Pu as a chronostratigraphic marker to constrain 210Pb ages in young Holocene sediments from four coastal locations of Cuba (Caribbean Sea). The selected sites typify a variety of deposition environments such as a bay, a gulf, a coastal lagoon and a river estuary. The vertical distributions of 210Pb (and 226Ra), 239,240Pu and 137Cs in the sediment cores were determined in order to quantify the sedimentation processes. Mean activity ratios of 0.04 ± 0.01 for 238Pu/239,240Pu and 0.3 ± 0.2 for 241Am/239,240Pu indicated that atmospheric nuclear weapon tests (NWT) fallout was the main source of the anthropogenic radionuclides. Marine sites (Havana Bay and Gulf of Batabano) were characterized by low or negligible signals of 137Cs, which impeded its use as a chronostratigraphic marker. In the Sagua River Estuary and the Guanaroca Lagoon, where mixing of fresh and saline waters take place, depth profiles of 137Cs and 239,240Pu were in good agreement. A simple model that assumes a well-mixed reservoir in surface ocean waters and constant sediment accumulation was used to interpret the 239,240Pu profiles. The model corroborated the 210Pb ages, except in the case of the highly mixed sediment cores from the Gulf of Batabano. The apparent mean residence time of 239,240Pu in the well-mixed reservoir ranges from 5 to 50 years, with longer timescales for marine sites. 239,240Pu showed to be a useful time tracer in coastal sediments where the 137Cs signal is very low. [ABSTRACT FROM AUTHOR]

Laboratories from 14 countries (with different levels of expertise in radionuclide measurements and 210Pb dating) participated in an interlaboratory comparison exercise (ILC) related to the application of 210Pb sediment dating technique within the framework of the IAEA Coordinated Research Project. The laboratories were provided with samples from a composite sediment core and were required to provide massic activities of several radionuclides and an age versus depth model from the obtained results, using the most suitable 210Pb dating model. Massic concentrations of Zn and Cu were also determined to be used for chronology validation. The ILC results indicated good analytical performances while the dating results didn't demonstrate the same degree of competence in part due to the different experience in dating of the participant laboratories. The ILC exercise enabled evaluation of the difficulties faced by laboratories implementing 210Pb dating methods and identified some limitations in providing reliable chronologies. • Interlaboratory comparison exercise (ILC) finds difficulties of the Pb-210 method. • ILC results indicate good analytical performance of the participants. • ILC dating results did not show the same degree of confidence. [ABSTRACT FROM AUTHOR]

Abstract: Since 1998 the highly polluted Havana Bay ecosystem has been the subject of a mitigation program. In order to determine whether pollution-reduction strategies were effective, we have evaluated the historical trends of pollution recorded in sediments of the Bay. A sediment core was dated radiometrically using natural and artificial fallout radionuclides. An irregularity in the 210Pb record was caused by an episode of accelerated sedimentation. This episode was dated to occur in 1982, a year coincident with the heaviest rains reported in Havana over the XX century. Peaks of mass accumulation rates (MAR) were associated with hurricanes and intensive rains. In the past 60 years, these maxima are related to strong El Niño periods, which are known to increase rainfall in the north Caribbean region. We observed a steady increase of pollution (mainly Pb, Zn, Sn, and Hg) since the beginning of the century to the mid 90s, with enrichment factors as high as 6. MAR and pollution decreased rapidly after the mid 90s, although some trace metal levels remain high. This reduction was due to the integrated coastal zone management program introduced in the late 90s, which dismissed catchment erosion and pollution. [Copyright &y& Elsevier]

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >2000 m) and analysed for 239,240Pu and 137Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of 210Pb, together with 14C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess 210Pb inventory was used to normalize 239,240Pu and 137Cs inventories for variable sediment fluxes. The 239,240Pu/210Pb xs ratio was uniform across the entire sea, with a mean value of 1.24×10−3, indicating homogeneous fallout of 239,240Pu. The 137Cs/210Pb xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of 239,240Pu/137Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of 239,240Pu in the water column and major sedimentation of 137Cs in the eastern basin. Although areas with water depths of >2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the 239,240Pu and 0.95% of the 137Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments. [Copyright &y& Elsevier]