Molecular Markers of Biogenic and Oil-Derived Hydrocarbons in Deep-Sea Sediments Following the Deepwater Horizon Spill

Abstract

Following the Deepwater Horizon oil spill (DWHOS), the formation of an unexpected and extended sedimentation event of oil-associated marine snow (MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation) demonstrated the importance of biology on the fate of contaminants in the oceans. We used a wide range of compound-specific data (aliphatics, hopanes, steranes, triaromatic steroids, polycyclic aromatics) to chemically characterize the MOSSFA event containing abundant and multiple hydrocarbon sources (e.g., oil residues and phytoplankton). Sediment samples were collected in 2010–2011 (ERMA-NRDA programs: Environmental Response Management Application – Natural Resource Damage Assessment) and 2018 (REDIRECT project: Resuspension, Redistribution and Deposition of Deepwater Horizon recalcitrant hydrocarbons to offshore depocenter) in the northern Gulf of Mexico to assess the role of biogenic and chemical processes on the fate of oil residues in sediments. The chemical data revealed the deposition of the different hydrocarbon mixtures observed in the water column during the DWHOS (e.g., oil slicks, submerged-plumes), defining the chemical signature of MOSSFA relative to where it originated in the water column and its fate in deep-sea sediments. MOSSFA from surface waters covered 90% of the deep-sea area studied and deposited 32% of the total oil residues observed in deep-sea areas after the DWHOS while MOSSFA originated at depth from the submerged plumes covered only 9% of the deep-sea area studied and was responsible for 15% of the total deposition of oil residues. In contrast, MOSSFA originated at depth from the water column covered only 1% of the deep-sea area studied (mostly in close proximity of the DWH wellhead) but was responsible for 53% of the total deposition of oil residues observed after the spill in this area. This study describes, for the first time, a multi-chemical method for the identification of biogenic and oil-derived inputs to deep-sea sediments, critical for improving our understanding of carbon inputs and storage at depth in open ocean systems.

Sediment Resuspension and Associated Extracellular Enzyme Activities Measured ex situ: A Mechanism for Benthic-Pelagic Coupling in the Deep Gulf of Mexico

“…Refractory organic matter from surface water productivity, which is usually enriched in lipid complexes following sedimentation (Rullkötter, 2006) may stimulate LIP activities in marine sediments. Petroleum hydrocarbons from natural seeps and the DWH fallout that accumulated in surficial sediments in our investigation area following the spill (Romero et al, 2021) represent additional substrates for LIP in the investigated sediments (Kamalanathan et al, 2018). A connection between petroleum hydrocarbons and LIP activities were also found in one of our earlier studies at OC26 where rapid LIP activities reflected degradation of sedimented oily particulate matter (known as marine oil snow) following the DWH oil spill (Ziervogel et al, 2016).…”

“…Experiments were performed at six deep-sea sites in the northern GOM. The sites were located in areas known for their deep-sea coral habitats (AT357, VK826, DC673; White et al, 2012;Fisher et al, 2014); for natural active oil and gas seepage (GC600, MC118;MacDonald et al, 2015;Conti et al, 2016;Martens et al, 2016); and for oil input during the Deepwater Horizon (DWH) oil spill in 2010 (OC26; Atlas and Hazen, 2011;Chanton et al, 2015;Diercks et al, 2021;Romero et al, 2021). Our aim was to examine whether resuspension of deep-sea sediments enhances activities of extracellular enzymes in overlying waters.…”

Resuspension, Redistribution, and Deposition of Oil-Residues to Offshore Depocenters After the Deepwater Horizon Oil Spill

“…Alkane ratios were used to identify natural vs. oil sources (carbon preference index: CPI (C25-C33) = odd Cn/ even Cn) if samples were weathered (low molecular weight alkanes: % n-alkanes = C14-C24/sum (C12-C37) * 100). Samples with CPI < 2.0 and % n-alkanes < 25% indicate a weathered petrogenic source (Xing et al, 2011;Romero et al, 2015Romero et al, , 2021Herrera-Herrera et al, 2020).…”