Local ¹³⁷Cs reference profile on Bohai Bay:Implications, methods and initial results

Reconstruction of geological processes during the last hundred years needs accurate dating methods. ¹³⁷Cs and ²¹⁰Pb dating methods are widely used at present. As coastal areas are vulnerable to the changes of river sediment supply, the local tidal conditions, and the effects of extreme weather events, the quantitative descriptions of their modern processes have been a bottleneck for the highresolution studies. Regional reference- profiles can help improve the precision of modern sediments dating. If regional ²¹⁰Pb_exc and ¹³⁷Cs reference-profiles could be established, they will play a very positive role in the interpretation of the dating results of modern sediments. In this paper, the relatively stable salt-marsh sites with little transported activity were selected along the coastal areas of Bohai Bay. Based on systematic sampling of trench walls and Eijkelkamp cores, the authors measured the ²¹⁰Pb, ²²⁶Ra and ¹³⁷Cs activities of subsamples by γ spectrometer, combined with the existing data in the study area. Consequently, the local reference-profiles were established, six types of ²¹⁰Pb_exc and ¹³⁷Cs activity-depth profiles were summarized, and the ¹³⁷Cs regional reference-profiles were prelimiarily obtained. ¹³⁷Cs maximum peak in the Bohai Bay is correlated with 1963, which could be used as the main time-marker of the coastal area. However, the second peak above the maximum peak detected in some cores can not be correlated with 1986 but is actually controlled by local environmental factors such as those indiacated at sites S4 and S5.