Sustained deposition of contaminants from the Deepwater Horizon spill

Abstract

The 2010 Deepwater Horizon oil spill resulted in 1.6–2.6 × 1010 grams of petrocarbon accumulation on the seafloor. Data from a deep sediment trap, deployed 7.4 km SW of the well between August 2010 and October 2011, disclose that the sinking of spill-associated substances, mediated by marine particles, especially phytoplankton, continued at least 5 mo following the capping of the well. In August/September 2010, an exceptionally large diatom bloom sedimentation event coincided with elevated sinking rates of oil-derived hydrocarbons, black carbon, and two key components of drilling mud, barium and olefins. Barium remained in the water column for months and even entered pelagic food webs. Both saturated and polycyclic aromatic hydrocarbon source indicators corroborate a predominant contribution of crude oil to the sinking hydrocarbons. Cosedimentation with diatoms accumulated contaminants that were dispersed in the water column and transported them downward, where they were concentrated into the upper centimeters of the seafloor, potentially leading to sustained impact on benthic ecosystems.

Isotopic composition of sinking particles: Oil effects, recovery and baselines in the Gulf of Mexico, 2010–2015

“…These high values are linked to the unusually high flux dominated by a phytoplankton bloom collected at that time (see Giering et al, 2018;Yan et al, 2016). We therefore excluded the first three cups from the trend analysis for D 14 C. For D 14 C, we observed depleted values starting in October 2010, followed by an increase over the sampling period and a change point around in July 2013.…”

“…During the DWH spill, marine oil snow may also have been produced at depth from the 1000-m deep subsurface plume which emanated from the busted well head and moved to the southwest (Camilli et al, 2010;Diercks et al, 2010). Sinking marine snow may have scavenged oil while sinking through the plume or through enhanced microbial activity in response to the released oil (Valentine et al, 2014), serving as a cleansing agent for the water column (Yan et al, 2016).…”

“…The site is about 70 km southeast of the Mississippi River Delta. A deployment during 2010-2011 is reported in Yan et al (2016) and is referred to as Deployment 0 in this study. Sample collection is reported from 25 August 2010 to 29 March 2015, through five deployments of the trap ( Table 1).…”

“…Isotope samples were obtained over roughly a year, from 28 June 2012 from the trap 30 mab. Sinking particles were collected in time-series sediment traps as described in Yan et al (2016) and Giering et al (2018). Before the traps were deployed, particle collection cups were filled with filtered seawater with NaCl added to a final salinity of 40 and with HgCl 2 added to form a 0.14% solution to act as a preservative.…”

“…Samples were split into subsamples using a rotary sample splitter (WSD-10, McLane Research Laboratories). Individual splits were used for different analysis (Yan et al, 2016;Giering et al, 2018) (Choi and Wang, 2004), and purified CO 2 prepared as graphite targets and analyzed by accelerator mass spectrometry (Vogel et al, 1984). Values are reported according to the D notation put forth in Stuiver and Polach (1977).…”