Its activity decreases with sediment depth and is used for determining the rates of sediment accumulation (mass accumulation rate – MAR), linear accumulation rates (linear accumulation rate – LAR) and for dating consecutive learn more sediment layers. The 210Pbex activity is determined from the total activity of this isotope 210Pbtot in the sediment layer under examination, from which the activity of one of the products of 226Ra radioactive decay, e.g. 214Bi, 214Pb, should be subtracted. Several geochronology models based

on the vertical distribution of 210Pb and using its radioactive decay equation have been developed. Which model is chosen depends on the environmental conditions of the investigated area, e.g. sediment processes Apoptosis inhibitor (erosion, deposition), sediment focusing and sediment stability. In the current study, two models of 210Pb activity variability along vertical profiles were employed to investigate the rates of sediment accumulation and sediment dating (Robbins, 1978 and Appleby, 1997). The first model, known as CF:CS (the Constant Flux Constant Sedimentation Rate

model), assumes that there is a constant flux of 210Pb and that the rate of sediment deposition is constant as well. With this model the sedimentation rate can be calculated using the slope of the line derived from the linear regression of ln210Pbex and the depth layer according to the following (equations Bierman et al. 1998): equation(1) Ax=A0e−bx,Ax=A0e−bx, equation(2) v=λb, where Ax – excess 210Pb activity at depth x [Bq kg− 1 d.m.], A0 – activity at the surface layer [Bq kg− 1 d.m.], b – the slope defined by regression through the data, x – depth [cm], v – sedimentation rate – LAR [cm year− 1] and λ – 210Pb radioactive decay constant (0.03114 year− 1). By using this model it is possible to determine sediment MARs, which are a measure of sedimentation where changes in sediment density with depth occur owing to sediment compaction. The sediment MAR is calculated using the slope of the line derived from 4��8C the

linear regression of ln210Pbex and the cumulative depth (Brush et al. 1982): equation(3) Am=A0e−bm,Am=A0e−bm, equation(4) ω=λb, where Am – excess 210Pb activity at cumulative depth m [Bq kg− 1 d.m.], A0 – activity in the surface layer [Bq kg− 1 d.m.], b – slope defined by regression through the data, m – cumulative depth [g cm− 2], ω – mass sediment accumulation rate – MAR [g cm− 2 year− 1] and λ – 210Pb radioactive decay constant (0.03114 year− 1]). The age of a given layer is calculated using the equation: equation(5) t=mω. The second model, known as CRS (the Constant Rate of Supply model), is based on the assumption that the supply of unsupported 210Pb to the sediment is constant in time while the initial excess 210Pb activity (A0) varies inversely with the sediment MAR – ω ( Goldberg, 1963 and Boer et al., 2006): equation(6) A0ω=const.A0ω=const.