Modeling detailed sedimentary 210Pb and fallout 239,240Pu profiles to allow episodic events: An application in Chesapeake Bay

Dependable sediment chronologies are essential to the interpretation of the sedimentary record of past environmental change. In the present article, we use high‐resolution chemical and radiochemical data as the basis for a numerical simulation of sediment accumulation, bioturbation, and episodic deposition or erosion in a dynamic estuary. We simulate episodic events by employing a time dependent sedimentation rate that we solve by finding a set of model parameters that describes depth profiles of both excess 210Pb and fallout 239,240Pu. We apply the model to depth distributions of these tracer nuclides in cores from upper‐, mid‐ and lower‐Bay sites in Chesapeake Bay. At the upper‐Bay site, combining chemical and radiochemical data permits us to recognize and to quantify the sediment deposition due to tropical storm Agnes (1972). At the lower‐Bay site, we demonstrate nonsteady sedimentation and propose plausible scenarios to account for it. Given adequate data, our model can provide information that is not available from steady‐state models.