226
wellhead with distribution extending toward the DeSoto Canyon to the northeast
and toward the Mississippi Valley (i.e., Mississippi Canyon) to the southwest.
Chanton et al. (2015) used radiocarbon as a tracer for petrocarbon deposition by
identifying areas of depleted radiocarbon in surface sediments. Using this approach,
they calculated that the seafloor extent of petrocarbon was 8400 km
2
, comprising up
to 14.4% of the total petroleum released and distributed primarily to the southwest
of the DWH wellhead in the Mississippi Valley along with depletion apparent at
sites in the DeSoto Canyon. Romero et al. (2017) used a suite of organic geochemical tracers to identify the deep-seafloor extent of oil residue (32,648 km
2
) and found
that deposition was primarily near the DWH wellhead and in the Mississippi Valley,
comprising up to 3.7% of the total petroleum released that was not recovered or
burned. Finally, Schwing et al. (2017a) utilized a short-lived radioisotope (excess
210
Pb)
approach to constrain the spatial extent of increased sediment flux, which resulted
in spatial seafloor coverage between 12,805 km
2
and 35,425 km
2
. Again, the primary deep-sea areas that were impacted by increased sediment flux extended from
the DWH wellhead southwest to the Mississippi Valley and northeast to the Desoto
Canyon. The highest seafloor coverage estimates from these various studies
(32,648–35,425 km
2
) were consistent with the spatial extent of daily surface petroleum coverage 39,600 km
2
and suggest that MOSSFA affected broad sections of the
continental slope and shelf where surface oil occurred (NRDA 2015; Stout et al.
2015). Despite the variability in spatial estimates between the various approaches,
they all suggest that MOSSFA was focused in certain areas of the deep GoM, specifically surrounding the DWH wellhead, in the Mississippi Valley and the DeSoto
Canyon. Bathymetric features such as the Mississippi Valley and the DeSoto Canyon
likely acted as focusing factors for MOSSFA. Focusing of MOSSFA in these areas
is also consistent with benthic biological impacts documented following DWH and
should be taken into account during future oil spills (Montagna et al. 2013; Baguley
et al. 2015: Schwing et al. 2015; Stout and German 2015; Schwing et al. 2017b,
2018a; Montagna and Girard 2020; Schwing and Machain Castillo 2020).
13.4 What Postdepositional Processes Took Place as a Result
of MOSSFA?
Following DWH, MOSSFA in the northern GoM, there were several postdepositional sedimentary processes that occurred. These processes were largely due to
the increased deposition of organic carbon (Brooks et al. 2015; Romero et al. 2015;
Schwing et al. 2015; Yan et al. 2016; Chanton et al. 2018; Giering et al. 2018).
Sedimentary total organic carbon (TOC) accumulation rates at sites up to 120 km
away from the DWH wellhead increased by two orders of magnitude during DWH
relative to downcore, pre-DWH measurements (Brooks et al. 2015; Romero et al.
2015). Yan et al. (2016) found an increase of up to an order of magnitude in organic
carbon sedimentation rates in sediment traps during and directly following DWH
P. T. Schwing et al.
wellhead with distribution extending toward the DeSoto Canyon to the northeast
and toward the Mississippi Valley (i.e., Mississippi Canyon) to the southwest.
Chanton et al. (2015) used radiocarbon as a tracer for petrocarbon deposition by
identifying areas of depleted radiocarbon in surface sediments. Using this approach,
they calculated that the seafloor extent of petrocarbon was 8400 km
2
, comprising up
to 14.4% of the total petroleum released and distributed primarily to the southwest
of the DWH wellhead in the Mississippi Valley along with depletion apparent at
sites in the DeSoto Canyon. Romero et al. (2017) used a suite of organic geochemical tracers to identify the deep-seafloor extent of oil residue (32,648 km
2
) and found
that deposition was primarily near the DWH wellhead and in the Mississippi Valley,
comprising up to 3.7% of the total petroleum released that was not recovered or
burned. Finally, Schwing et al. (2017a) utilized a short-lived radioisotope (excess
210
Pb)
approach to constrain the spatial extent of increased sediment flux, which resulted
in spatial seafloor coverage between 12,805 km
2
and 35,425 km
2
. Again, the primary deep-sea areas that were impacted by increased sediment flux extended from
the DWH wellhead southwest to the Mississippi Valley and northeast to the Desoto
Canyon. The highest seafloor coverage estimates from these various studies
(32,648–35,425 km
2
) were consistent with the spatial extent of daily surface petroleum coverage 39,600 km
2
and suggest that MOSSFA affected broad sections of the
continental slope and shelf where surface oil occurred (NRDA 2015; Stout et al.
2015). Despite the variability in spatial estimates between the various approaches,
they all suggest that MOSSFA was focused in certain areas of the deep GoM, specifically surrounding the DWH wellhead, in the Mississippi Valley and the DeSoto
Canyon. Bathymetric features such as the Mississippi Valley and the DeSoto Canyon
likely acted as focusing factors for MOSSFA. Focusing of MOSSFA in these areas
is also consistent with benthic biological impacts documented following DWH and
should be taken into account during future oil spills (Montagna et al. 2013; Baguley
et al. 2015: Schwing et al. 2015; Stout and German 2015; Schwing et al. 2017b,
2018a; Montagna and Girard 2020; Schwing and Machain Castillo 2020).
13.4 What Postdepositional Processes Took Place as a Result
of MOSSFA?
Following DWH, MOSSFA in the northern GoM, there were several postdepositional sedimentary processes that occurred. These processes were largely due to
the increased deposition of organic carbon (Brooks et al. 2015; Romero et al. 2015;
Schwing et al. 2015; Yan et al. 2016; Chanton et al. 2018; Giering et al. 2018).
Sedimentary total organic carbon (TOC) accumulation rates at sites up to 120 km
away from the DWH wellhead increased by two orders of magnitude during DWH
relative to downcore, pre-DWH measurements (Brooks et al. 2015; Romero et al.
2015). Yan et al. (2016) found an increase of up to an order of magnitude in organic
carbon sedimentation rates in sediment traps during and directly following DWH
P. T. Schwing et al.