A novel application of radionuclides for dating sediment cores from sandy, anthropogenically disturbed estuaries

Reliablesedimentationhistoriesaredifficulttoobtaininsandyoranthropogenicallyimpactedcoastalsystems with disturbed sediment profiles and low initial radionuclide activities. This study addresses the problem using radionuclides in sediment cores from Naples Bay estuary, Florida, USA. Non-steady sedimentation and nuclide scavenging processes are shown to limit application of traditional radiometric dating models in this system. Whole-core inventories of excess 210 Pb activity ( 210 Pbxs) varied from 21 to 96dpmcm � 2 among sites, and initial sediment 210 Pbxs activitieswerelow,decreasingnon-uniformlywithdepthinmostcores.Activitiesofthreeradioisotopesusedforsediment dating ( 226 Ra, 210 Pb, and 137 Cs) were compared with grain size and organic matter (OM) distributions to assess the factors that influence accumulation of radionuclides. Regression analysis indicated that radionuclide activities were more strongly correlated with OM content than with grain size parameters, and a novel OM-normalisation procedure was developed to correct for preferential nuclide associations. Normalised 210 Pbxs profiles provide evidence for shifts in sedimentation rates and episodic erosion events in regions of the estuary where anthropogenic disturbance is known to have occurred. Our results emphasise the need to consider radionuclide scavenging by OM in sandy coastal sediments when establishing sedimentation histories. Additional keywords: Cs-137, estuaries, grain size effect, organic matter, Pb-210, preferential scavenging, radioisotopes, Ra-226.