Gregg R. Brooks

The deposition/accumulation of oil on the seafloor is heavily influenced by sediment/texture/composition and sedimentary processes/accumulation rates. The objective of this chapter is to provide a baseline of Gulf of Mexico sediment types and transport/depositional processes to help guide managers where oiled sediments may be expected to be deposited and potentially accumulate on the seafloor in the event of a future oil spill. Based solely on sediments/processes/accumulation rates, regions most vulnerable to oil deposition/accumulation include the deep eastern basin, followed by the western/southwestern basin, and north and west continental margins. The least vulnerable regions include the northwest Cuban shelf and the carbonate-dominated west Florida shelf and Campeche Bank. This is intended to be used as a general, “first cut” tool and does not consider local variations in sediments/processes.

This chapter provides a summary of the scientific knowledge about sediments and fauna in the margin of northwest Cuban shelf. Little scientific information is publicly available, and so much of what is discussed here is the result of the scientific expedition to the region in May 2017 on board the R/V Weatherbird II as part of the GoMRI consortium, C-IMAGE (see Foreword, this book). The goal was to set broad environmental baselines against which to evaluate the impacts of any potential future oil spill or other disturbance in the Gulf of Mexico (GoM). The chapter is organized in three parts: (1) overview of the geographical setting of Cuban margin of GoM; (2) sediment characterization including texture, composition, and geochronology of sediment cores; and (3) characterization of key bioindicators of oil impact: mollusks, meiofauna, and foraminifera.

The Deepwater Horizon (DWH) blowout led to a depositional pulse in the northeast Gulf of Mexico in the Fall of 2010 associated with an observed Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) event. A time series (2010–2016) of annually collected sediment cores at four sites characterize the sedimentary response to the event, post-event, and stabilization/recovery. The depositional pulse (2010–2011) was characterized by high sedimentation rates with little to no bioturbation and large excursions in % silt. The lack of changes in sediment composition indicate that the same sediment sources dominated during the event, but the rates of sedimentation increased. In the years following the event (2011–2012), sedimentation rates were lower, and bioturbation was absent, and the initial excursions in % silt began to become undetectable in the sedimentary record. Between 2013 and 2016, a spatially and temporally variable return of bioturbation was detected at most sites. Sedimentation rates at all sites remained low, but increases in 234Thxs apparent mass accumulation rates indicated a return of bioturbation and potential stabilization and/or recovery of the sedimentary system. The deepest site (~1500 m) did not have any indication of bioturbation as of the 2016 collections, which may reflect a lack of recovery or that bioturbation was never present. In 2012, 210Pbxs age dating began to resolve the depositional pulse suggesting it may be applied to determine changes in the pulse deposit over time, and/or its preservation in the sedimentary record. Factors that may influence preservation include burial, bioturbation, degradation of the pulse signature, and remobilization of pulse sediments.

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