DOCUMENTING THE SUSPENDED AND BOTTOM SEDIMENT DYNAMICS OF A TWO ESTUARINE TURBIDITY MAXIMUM SYSTEM USING 7BE AND 234TH

In recent years, there has been a growing interest in understanding the processes that affect suspended sediment dynamics and deposition in estuarine systems. Traditional paradigms of estuarine circulation are being modified to account for new theories and observations. Specifically, secondary turbidity maxima have been described in several estuarine systems, but their role in the dynamics and distribution of suspended and bottom sediments still is not fully understood. Short-lived radionuclides such as ⁷Be and ²³⁴Th may prove invaluable for fully understanding sediment behavior in these complex systems.

Weekly cruises were undertaken spring and fall of 2002 in the York River estuary, VA, in order to better understand the coupling between the main estuary turbidity maximum (ETM), the secondary estuarine turbidity maximum (STM) and the dynamic properties of the underlying seabed. Profiles of temperature, salinity and TSS concentrations along the estuary were generated via Conductivity-Temperature-Depth (CTD) and Optical Backscatter Sensor (OBS) measurements. Suspended and bottom sediment analysis included isotopic measurements, porosity and grain size analysis.

Observations and measurements from the York River are presented documenting the hydrodynamic setting as well as suspended and bottom sediments. Results detail the particle histories of the sediments making up the erosional and depositional zones associated with the ETM and STM. Preliminary results suggest significant deposition of ⁷Be only within the ETM and STM depositional zones, supporting the hypothesis that the hydrodynamic regime associated with formation and migration of turbidity maxima controls sediment dynamics in this estuarine system.