Immobility of 210Pb in Black Sea sediments

We measured 210Pb in a core from the deep Black Sea which contained a turbidite of low 210Pb activity surrounded above and below by pelagic sediments of much higher activity to evaluate in situ210Pb mobility under the anoxic, moderately sulfidic conditions. By measuring at millimeter scales across the distinct laminae-turbidite contacts and modeling the observed profile, we estimated a lower limit of the Kd of 107(Deff = 5 × 10 −13). This result increases confidence in sediment chronologies from the Black Sea based on 210Pb because it implies that profiles will not be altered significantly by diffusive transport of 210Pb Below the turbidite the 210Pb-inferred accumulation rate was 50 g/m2-a which is lower than laminae-based estimates by a factor of 3–4.