227
compared to 2011, and
14
C depletion of this particulate organic carbon (POC) was
observed for 3 years after the spill (Chanton et al. 2018). The increased TOC accumulation rates (including oil residue) delivered to the seafloor by MOSSFA caused
an increase in the abundance of oil-degrading microbes (Kimes et al. 2013; Mason
et al. 2014). Experimental evidence suggests that marine snow may have impeded
the degradation of oil residue by up to 40% and that other MOSSFA biogenic
organic material was preferentially degraded prior to oil-residue components
(Rahsepar unpublished; Langenhoff et al. 2020). The increased respiration of
organic carbon caused depleted surface sediment oxygen and intensification of
reducing conditions up to 3 years following DWH (Hastings et al. 2016, 2020). The
intensification of reducing conditions likely limited bioturbation, which may have
in turn prolonged the reducing conditions in the surface sediment. There is evidence that bioturbation was present at the majority of the study sites throughout the
northern GoM beginning in 2013 (Larson et al. 2018; Schwing et al. 2018a; Larson
et al. 2020). The return of bioturbation in 2013 was consistent with the return to
steady state of redox-sensitive metals (Fig. 13.3) from 2013 to 2016 (Hastings
et al. 2016, 2020).
13.5 Can MOSSFA Be Preserved in the Sedimentary
Record?
The preservation of oil residue in the sediments associated with DWH and the sedimentary event in the geologic record has been demonstrated using multiple tracers
(Larson et al. 2020; Romero et al. 2020; Radović et al. unpublished; Larson et al.
2018). There was a preserved stratigraphic transition in grain size (finer or coarser
depending on location) for the period of 2010–2011 in the majority of time series
stations collected throughout the northern GoM relative to pre-DWH and postDWH sedimentary intervals surrounding DWH (Larson et al. 2018; see Larson
et al. 2020). Short-lived radioisotope profiles, specifically excess
210
Pb, were also
able resolve the preservation of DWH, which manifested as a plateau in activity
and was consistent with increased sedimentation (Larson et al. 2018, 2020).
Radović et al. (unpublished) utilized polar lipid biomarkers, pigments, hydrocarbons, and stable isotopes of benthic foraminifera (Schwing et al. 2018b: Schwing
and Machain Castillo 2020), to demonstrate the multi-year preservation of DWH
in MOSSFA. The most recalcitrant DWH petroleum-derived compounds are likely
to persist in the sedimentary record on the order of a decade if only degradation is
taken into account (Romero et al. 2020; Gros et al. 2014; Turner et al. 2014;
Romero et al. 2017). However, oxygenated weathering products derived from saturated and aromatic DWH compounds may persist longer (Aeppli et al. 2014; White
et al. 2014). Regardless of degradation and weathering, downslope transport of
sediments must also be taken into account, as discussed in Larson et al. (2020) and
Romero et al. (2020).
13 The Sedimentary Record of MOSSFA Events in the Gulf of Mexico: A Comparison…
compared to 2011, and
14
C depletion of this particulate organic carbon (POC) was
observed for 3 years after the spill (Chanton et al. 2018). The increased TOC accumulation rates (including oil residue) delivered to the seafloor by MOSSFA caused
an increase in the abundance of oil-degrading microbes (Kimes et al. 2013; Mason
et al. 2014). Experimental evidence suggests that marine snow may have impeded
the degradation of oil residue by up to 40% and that other MOSSFA biogenic
organic material was preferentially degraded prior to oil-residue components
(Rahsepar unpublished; Langenhoff et al. 2020). The increased respiration of
organic carbon caused depleted surface sediment oxygen and intensification of
reducing conditions up to 3 years following DWH (Hastings et al. 2016, 2020). The
intensification of reducing conditions likely limited bioturbation, which may have
in turn prolonged the reducing conditions in the surface sediment. There is evidence that bioturbation was present at the majority of the study sites throughout the
northern GoM beginning in 2013 (Larson et al. 2018; Schwing et al. 2018a; Larson
et al. 2020). The return of bioturbation in 2013 was consistent with the return to
steady state of redox-sensitive metals (Fig. 13.3) from 2013 to 2016 (Hastings
et al. 2016, 2020).
13.5 Can MOSSFA Be Preserved in the Sedimentary
Record?
The preservation of oil residue in the sediments associated with DWH and the sedimentary event in the geologic record has been demonstrated using multiple tracers
(Larson et al. 2020; Romero et al. 2020; Radović et al. unpublished; Larson et al.
2018). There was a preserved stratigraphic transition in grain size (finer or coarser
depending on location) for the period of 2010–2011 in the majority of time series
stations collected throughout the northern GoM relative to pre-DWH and postDWH sedimentary intervals surrounding DWH (Larson et al. 2018; see Larson
et al. 2020). Short-lived radioisotope profiles, specifically excess
210
Pb, were also
able resolve the preservation of DWH, which manifested as a plateau in activity
and was consistent with increased sedimentation (Larson et al. 2018, 2020).
Radović et al. (unpublished) utilized polar lipid biomarkers, pigments, hydrocarbons, and stable isotopes of benthic foraminifera (Schwing et al. 2018b: Schwing
and Machain Castillo 2020), to demonstrate the multi-year preservation of DWH
in MOSSFA. The most recalcitrant DWH petroleum-derived compounds are likely
to persist in the sedimentary record on the order of a decade if only degradation is
taken into account (Romero et al. 2020; Gros et al. 2014; Turner et al. 2014;
Romero et al. 2017). However, oxygenated weathering products derived from saturated and aromatic DWH compounds may persist longer (Aeppli et al. 2014; White
et al. 2014). Regardless of degradation and weathering, downslope transport of
sediments must also be taken into account, as discussed in Larson et al. (2020) and
Romero et al. (2020).
13 The Sedimentary Record of MOSSFA Events in the Gulf of Mexico: A Comparison…