High-Resolution Investigation of Event Driven Sedimentation: Northeastern Gulf of Mexico

A rapid sedimentation pulse in the northeast Gulf of Mexico, associated with the Deepwater Horizon blowout in 2010, provided a unique opportunity to investigate a depositional event in real time and at very high resolution. Sediment cores were collected annually (2010-2016) from four sites and sub-sampled at 2 mm resolution to identify and characterize the sedimentary signature, as well as geochronology and accumulation rates using excess Lead-210 ( ²¹⁰ Pb _xs ) and excess Thorium-234 ( ²³⁴ Th _xs ). The “time-series” collection of sediment cores on an annual basis allowed for the identification of changes in sedimentation on monthly to annual time-scales, which define the depositional pulse (2010-2011), initial post-event sedimentary impact and response (2011-2012), and post-event stabilization and preservation (2013-2016). The 2010 depositional pulse was short-lived ( < 1 year) with ²³⁴ Th _xs inventories and mass accumulation rates (MARs) indicating higher sedimentation rates and an absence of bioturbation as compared to subsequent years. The initial post-event impact/response (2011-2012) exhibited lower ²³⁴ Th _xs inventories and MARs indicating lower sedimentation rates. The stabilization in sedimentation (2013-2016) was indicated by site-specific apparent increases in MARs that are not supported by increased ²³⁴ Th _xs inventories, reflecting the re-establishment of bioturbation. Initially, ²¹⁰ Pb _xs was unable to detect the sedimentation pulse, but with subsequent sedimentation and burial, it begins to resolve the event after 3-5 years. The ability to resolve the sedimentation pulse and the following short-term response was possible due to the high-resolution sampling and analysis, unconventional methodologies, and utilization of high sedimentation rates.