Pb-dating of recent sediments with the χ-mapping CF and CSAR models. On the attractors.

Conventional Pb-dating models use assumptions on sedimentary conditions that allow for analytical formulations. The novel χ-mapping models use numerical methods to generate and test a large number (∼10) of potential solvers. Empirical data (excess Pb vs.

Pb-dating of sediments with models assuming a constant flux: CFCS, CRS, PLUM, and the novel χ-mapping. Review, performance tests, and guidelines.

The Pb-based method has been widely used for five decades to determine absolute ages in recent sediments on the centennial scale. Decoding a chronology from the empirical data set requires a series of assumptions that define a mathematical model of the sedimentary conditions. This work aims to provide a comprehensive review of the fundamentals of the existing family of models assuming a constant flux of excess Pb at the sediment surface, namely the CFCS, CRS, and PLUM models, and to present the novel χ-mapping versions of the CFCS and CF models.

Pb-based dating of recent sediments with the χ-mapping version of the Constant Sediment Accumulation Rate (CSAR) model.

The Pb-based method aims at determining the absolute age of recent sediments on the centennial scale. A family of models assumes that at the sediment-water interface the flux of unsupported Pb (Pb), F, relates to its initial activity concentration, A, and the mass sedimentation rate, w, as: F=Aw. Additional specific assumptions that allow for analytical formulations of the models are: i) constant A (CIC), constant F (CF), and constant F with constant w (CFCS).

Kinetic reactive transport explains distinct subsurface deposition patterns of pollutants in sediments. The case of the Sellafield-derived U, Cs and Pu in the Esk Estuary, UK.

The kinetics of the uptake of pollutants by solids in sediments interacts with transitional eddy diffusivity in the pore fluid, leading to different depth-distribution patterns. This work aims to gain insights into the still poorly understood behaviour in the marine environment of the anthropogenic U, a recently postulated tracer of water masses. It is hypothesized that the transition from mobile U(VI) to highly particle-reactive U(IV) in the anoxic zone of the sediment produces a subsurface deposition pattern.

Depth-distributions and migration of fallout radionuclides in mountain soils from Chréa National Park (Algeria): The role of rhizospheres.

The distribution and migration of artificial fallout radionuclides in natural soils has been profusely studied for assessing radioecological impacts and predicting their long-term behaviour, among other topics. Despite the standardized use of the analytical solutions of a simplified convection-diffusion equation (CDE), there are still some concerns and open questions. This work is aimed at contributing to the understanding of basic processes governing the distribution of fallout radionuclides in vegetated soils with rhizospheres.

Experimental study on the use of granulometric speciation for the radiometric dating of recent sediments.

Theoretical and experimental studies have shown that activity concentrations of fallout radionuclides (such as Cs and excess Pb) decrease with particles size in aqueous suspensions. This paper is aimed at reviewing the theoretical fundamentals for granulometric speciation of radionuclides, and at exploring its practical use in the analytical context of gamma spectrometry for the radiometric dating of recent sediments, with view to: i) improving the detection of Cs (since its use as independent chronostratigraphic mark is challenging in the southern hemisphere because its low fallout rate), ii) supporting refined CIC models and normalization techniques in Pb-based radiogeochronologies. The work uses surface sediments sampled from the Tinto Estuary (SW Spain), affected by mining and phosphate-fertilizer industries, and from the Ankobra Estuary (Ghana), affected by intensive artisanal gold-mining.

A (210)Pb-based chronological model for recent sediments with random entries of mass and activities: Model development.

Unsupported (210)Pb ((210)Pbexc) vs. mass depth profiles do not contain enough information as to extract a unique chronology when both, (210)Pbexc fluxes and mass sediment accumulation rates (SAR) independently vary with time. Restrictive assumptions are needed to develop a suitable dating tool.

Why would we use the Sediment Isotope Tomography (SIT) model to establish a 210Pb-based chronology in recent-sediment cores?

After half a century, the use of unsupported (210)Pb ((210)Pbexc) is still far off from being a well established dating tool for recent sediments with widespread applicability. Recent results from the statistical analysis of time series of fluxes, mass sediment accumulation rates (SAR), and initial activities, derived from varved sediments, place serious constraints to the assumption of constant fluxes, which is widely used in dating models. The Sediment Isotope Tomography (SIT) model, under the assumption of non post-depositional redistribution, is used for dating recent sediments in scenarios in that fluxes and SAR are uncorrelated and both vary with time.