236
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
234
Th xs 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,
210
Pb xs 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.
Keywords Sediment · Chronology · MOSSFA · Short-lived radioisotopes ·
Sedimentation
14.1 Introduction
The Deepwater Horizon (DWH) blowout resulted in multiple sequences of events
leading to the deposition of sediment and oil-contaminated sediment to the deep-sea
benthos and subsequent integration into the sedimentary system. Beginning in April
2010, the DWH blowout led to the release of oil and gas at a water depth of ~1500 m
in the northeastern Gulf of Mexico (NEGoM) for a duration of 87 days (Passow and
Hetland 2016). The released oil formed a rising plume from the leak at the seafloor
to the sea surface, a subsurface plume at ~1000 m water depth (Diercks et al. 2010;
Joye et al. 2011), and a sea surface oil slick (Thibodeaux et al. 2011). A variety of
strategies to stop the release of oil and mitigate impacts were utilized to contain,
remove, and influence the distribution and degradation (biotic and abiotic) of
released oil (US Coast Guard 2010; BOEM 2011). This included the addition of
dispersants (Corexit) at the wellhead as well as at sea surface slicks (Yan et al.
2016), skimming and burning at the sea surface, water release from the Mississippi
River, and the addition of drilling mud at the wellhead (Liu et al. 2018).
The DWH blowout occurred in a region that is sedimentologically complex
(Fig. 14.1a). West of the DeSoto Canyon seafloor sediments are dominantly siliciclastic, associated with Mississippi River discharge. East of the DeSoto Canyon
seafloor sediments are dominantly carbonate, associated with the west Florida
Platform and low river influence (Balsam and Beeson 2003; Holmes 1976; Harbison
1968). This resulted in the potential impacts of oil released in both siliciclastic and
carbonate sedimentary regimes.
R. A. Larson et al.
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
234
Th xs 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,
210
Pb xs 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.
Keywords Sediment · Chronology · MOSSFA · Short-lived radioisotopes ·
Sedimentation
14.1 Introduction
The Deepwater Horizon (DWH) blowout resulted in multiple sequences of events
leading to the deposition of sediment and oil-contaminated sediment to the deep-sea
benthos and subsequent integration into the sedimentary system. Beginning in April
2010, the DWH blowout led to the release of oil and gas at a water depth of ~1500 m
in the northeastern Gulf of Mexico (NEGoM) for a duration of 87 days (Passow and
Hetland 2016). The released oil formed a rising plume from the leak at the seafloor
to the sea surface, a subsurface plume at ~1000 m water depth (Diercks et al. 2010;
Joye et al. 2011), and a sea surface oil slick (Thibodeaux et al. 2011). A variety of
strategies to stop the release of oil and mitigate impacts were utilized to contain,
remove, and influence the distribution and degradation (biotic and abiotic) of
released oil (US Coast Guard 2010; BOEM 2011). This included the addition of
dispersants (Corexit) at the wellhead as well as at sea surface slicks (Yan et al.
2016), skimming and burning at the sea surface, water release from the Mississippi
River, and the addition of drilling mud at the wellhead (Liu et al. 2018).
The DWH blowout occurred in a region that is sedimentologically complex
(Fig. 14.1a). West of the DeSoto Canyon seafloor sediments are dominantly siliciclastic, associated with Mississippi River discharge. East of the DeSoto Canyon
seafloor sediments are dominantly carbonate, associated with the west Florida
Platform and low river influence (Balsam and Beeson 2003; Holmes 1976; Harbison
1968). This resulted in the potential impacts of oil released in both siliciclastic and
carbonate sedimentary regimes.
R. A. Larson et al.