Anthropocene Mississippi Delta Sediment Budget Documenting Sedimentary Processes and Human Impacts

We present the first integrated regional subaqueous Mississippi River sediment budget to better understand how declines in sediment load from the Mississippi River over the 20th and 21st centuries contributed to the development and retrogradation of the submarine Mississippi River Delta Front (MRDF). This retrogradation can be partly attributed to downslope mass transport, which may move sediment more rapidly than replenishment from proximal fluvial sources. 210Pb/137Cs geochronology from 67 sediment cores was utilized to calculate apparent sediment mass accumulation rates (MAR) during the 20th and early 21st centuries. 210Pb and 137Cs regional maps documenting MARs from 1953 to 2025 were created to document sediment accumulation across the MRDF, which identified up to 73.8 Mt/y. A regional mass-accumulation budget for the subaqueous delta of this river-dominated system, when compared to mean 1939–2010 sediment discharge rates, indicates an approximate time-averaged retention of 25% of fluvial sediment discharge from major historical outlets on the MRDF. Furthermore, patterns of accumulation record the effects of major anthropogenic reductions in fluvial sediment load, as well as the complex interactions between oceanic and gravity-driven processes.