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Working on an experimental dataset to derive descriptive parameters with well-known procedures appears to be a straightforward process. However, due to the complexity of environmental systems, the procedures cannot be completely defined, and commonly hypothesis are required to obtain final results. These degrees of freedom cause a spread in results that is often wider than the experimental uncertainties and that should be taken into account in the measurement accuracy estimation. As an example of this issue, the sources of uncertainty, including reproducibility, that occur in dating marine and lacustrine sediment cores with the 210Pb methodology are discussed in this paper. The IAEA Coordinated Research Project (CRP) "Study of Temporal Trends of Pollution in Selected Coastal Areas by the application of Isotopic and Nuclear Tools" promoted this discussion, its main objective being the determination of a streamlined, harmonised and validated methodology for marine sediment dating. The uncertainties estimated from experimental data and mathematical propagated must be complemented with reproducibility contribution: some elements are specific for the 210Pb method (mixed layer, finite thickness of layers and identification of the equilibrium depth), while others are more general (exponential fitting and data interpolation). The final spreading of results can be mainly controlled by reproducibility, and efforts are needed to standardise procedures to reduce the effect of reproducibility and to better estimate the overall uncertainty of measurements. It is necessary to underline the importance of a thorough (a-priori) cost-effective analysis of the uncertainty evaluation of the measurement results in relation to the aim of the study, taking primarily into account the overall accuracy required case by case. • In 210 Pb dating models, there is low reproducibility of uncertainties. • Data interpolation and equilibrium depth choice affect constant flux dating results. • Procedures to fit 210 Pb data and surface mixed layer affect CFCS dating results. • The final spreading of dating uncertainties can be controlled by reproducibility. [ABSTRACT FROM AUTHOR]

Abstract: The DYFAMED site (Ligurian Sea, 43°25′N; 7°52′E) has been the subject of multidisciplinary research since 1987, including the study of atmospheric deposition of metals and their association with marine particles in the water column. On the other hand, the attention paid to the underlying sediments as the ultimate repository of elements, particularly pollutants, has been considerably lesser. Through the combined use of 210Pb chronologies and elemental analysis, we studied the concentrations and fluxes of trace metals (Zn, Pb, Ni, Cu, Cr) in a sediment core collected from ∼2300m water depth at the seafloor beneath DYFAMED. Surface metal enrichment during the 20th century is apparent in the case of Pb, Zn and Cu (maximum enrichment factors 1.5, 1.2 and 1.4, respectively). A comparison with published data suggests that atmospheric deposition is the main entrance route of anthropogenic trace metals accumulated in the recent sediments, while lateral advection of sediments by currents and sediment gravity flows is proposed to account for the pre-industrial concentrations of metals. Recent atmospheric inputs of Pb and Cu are more efficiently stored in sediments with respect to Zn, most of which is apparently advected elsewhere. [Copyright &y& Elsevier]

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]

The development of the Grijalva-Usumacinta river basin exerts modifications on its discharge area. A sediment core was studied to reconstruct environmental changes and trace element contamination status during the past 45 years. 210Pb-derived mass accumulation rates indicate higher sediment input to the area since 1995, related to increased precipitation and floodings in the catchment area. Sediments show finer particles from the late 1970s on, likely related to dams construction upriver and/or land use changes. Heavy metal enrichment factors (EF < 2) suggest minimum contamination. Benthic foraminifera and redox-sensitive - elements (As, Ba, Co, Cr, Cu, Ni, Pb, V and Zn) indicate the sediments before 2000 were deposited under oxygenated conditions. Afterwards, environmental conditions changed and benthic foraminifera and dinocysts assemblages changed suggesting eutrophication and lower oxygen conditions during the last 20 years. Monitoring should be continued to assess eutrophication/hypoxic/pollution trends that could become deleterious to the marine biota. • Sediments from past 45 years record environmental changes in the marine area off the largest river in southern Gulf of Mexico • Mass accumulation rates indicate higher sediment input to the area since 1995. • Higher sediment input related to increased precipitation and flooding in Tabasco City and the catchment area. • Grain size variation reflects land use change and damming since the 1980s. • Benthic Foraminifera and Dinocysts indicate a process of eutrophication in bottom waters during the last 20 years. [ABSTRACT FROM AUTHOR]

The Campeche Sound is the major offshore oil producing area in the Southern Gulf of Mexico (SGoM). To evaluate the impact of oil related activities in the ocean floor sediments, we analyzed the geochemical (major and trace element, organic carbon and hydrocarbon concentrations) and biological (benthic foraminifera) composition of 62 superficial sediment samples, from 13 to 1336 m water depth. Cluster and Factor analysis of all the variables indicate that their distribution patterns are mainly controlled by differences between the terrigenous and carbonate platforms in the SGoM. Benthic foraminiferal assemblages were abundant and diverse, and their distribution patterns are mainly determined by water depth and sedimentary environment. However, most of the abundant species are opportunistic and/or low-oxygen tolerant, and many of their tests show oil stains and infillings, characteristic of oil polluted locations, suggesting the environment has been modified by natural seepage or oil-related activities. To determine if these conditions are natural or anthropogenic in origin, pre - industrial settings should be studied. Organic carbon (Corg) content (0.6–2.9%) and total hydrocarbon concentrations (PAHs 1.0–29.5 μg kg−1) were usually higher around the oil platforms area, the natural hydrocarbon seeps ("chapopoteras") area and offshore rivers, but there is no accumulation of oil related trace elements in these areas. However, the comparison with international sediment quality benchmarks indicates that Cd, Cr and Ni concentrations are above the threshold effect level, and also As, Ba and Cu are above the probable effect level benchmarks, which indicate that these element concentrations might be of potential ecological concern. Comprehensive studies involving different proxies, and assessing pre-industrial conditions, must be undertaken before assessing environmental health of marine benthic ecosystems. • Impact of oil related activities on ocean floor sediments was assessed. • Benthic Foraminifera (microbenthos) show impact of various oil derived sources. • Concentrations of As, Ba and Cu might be of potential ecological concern.. • Organic carbon and PAHs content are greater in oil exploitation and seep areas. • Campeche Bay is affected by multiple stressors, both natural and anthropogenic. [ABSTRACT FROM AUTHOR]

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]

The accumulation rates of sediment and major constituents in three different geographic areas of the Alboran Sea have been assessed by means of 210Pb and 137Cs concentration profiles. Mixing is present in the top layer of the sedimentary column, with mixing coefficients estimated to range from 0.2 to 15 cm2 yr−1. Overall, apparent sedimentation rates for the last 100 years range from 0.014 to 0.182 g cm−2 yr−1 and show a tendency to decrease with distance to the coast and water column depth. However, specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation. Particularly noticeable are the feeding role of submarine canyons, the trapping effect of slope terraces and the isolation caused by ridges. Sediment accumulation induced by turbiditic flows is also observed north of the Almeria–Oran area. Excess 210Pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas. This is also evidenced by comparison of bottom sediment with the sediment trap data available from the Malaga area. We estimate that the particle advective input below 30 m above the bottom accounts for as much as 50–70% of the material that is ultimately deposited onto the sea floor. The greater abundance of lithogenic material in the Malaga zone (∼80%) reflects its larger input in the western Alboran Sea. Conversely, carbonate contents increase from less than 20% in this area to about 30% in the Almeria–Oran zone, reflecting the lesser importance of the dilution by lithogenic components. Biogenic silica was only detected in some surface samples, and no significant preservation was observed below the Eh boundary. Abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the Alboran Sea: higher in the western part, due to the presence of the Western Alboran Gyre. However, near-bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area. Finally, from comparisons with sediment trap data, the degradation of organic matter has been estimated to be approximately 30–40% of what reaches the bottom. [Copyright &y& Elsevier]

Discusses a study which assessed the sediment, carbon and nitrogen accumulation rates along a high-productivity area, Gerlache Strait, Antarctica. Sample collection and analytical methods; Results; Discussion.