Monthly Scale Resolution of Sedimentary Processes Using 234Th Inventories and Mass Accumulation Rates: Lessons from the 2010 DwH Event.

Within a few months following the 2010 DWH blowout, a depositional pulse was recorded in the Desoto Canyon region of the NE Gulf of Mexico (GoM). Interpreted as a response to a massive marine snow event that originated in the overlying surface waters, this depositional pulse resulted in an ~1 cm thick layer of sediments blanketing the seafloor between ~200 and >1500 m water depths. Excess ²³⁴Th age dating (~4-5 month time period) was utilized on a time series of cores collected between 2010 and 2014 to resolve the depositional pulse, as well as compare to subsequent years on the same monthly time scale. Time-series data show: 1) a well-defined, short-lived, depositional pulse recorded as increases in excess ²³⁴Th inventories and mass accumulation rates (MAR) in cores collected between Nov. 2010 and Feb. 2011, 2) a rapid decrease in excess ²³⁴Th inventories in 2011, followed by general stability over the following 3 years, which is likely indicative of “natural” sedimentation patterns and variability on this time-scale, 3) increases in MAR, with little to no change in inventory, at some sites during 2013/2014 likely due to the reestablishment of bioturbation that mixed excess ²³⁴Th downcore, giving the impression of higher MAR that is not supported by ²³⁴Th inventories. Consequently, excess ²³⁴Th inventories and MAR can be useful, but must be used in conjunction to determine if data represent deposition, and/or bioturbation/mixing. Continuation of the time series will further establish the natural system variability, as well as document the recovery of the benthic system.