245
14.5 Stabilization/Recovery: Post-event (2013–2016)
Beginning ~3 years after the DWH blowout and associated depositional pulse, there
were indications of variability in the evolution of the sedimentary system as it stabilized/recovered. At the time-series sites collected between 2013 and 2016, lower
234
Th xs Inventories did remain consistent with the postdepositional pulse Inventories
for 2011 and 2012 indicating continued lower rates of sedimentation (Fig. 14.2).
The
234
Th xs MARs exhibited specific increases at different collection years. Site
DSH08 exhibited an apparent increase in
234
Th xs MAR (A-MAR) beginning in
August 2013, while sites M04 and PCB06 recorded apparent increases in
234
Th xs
MAR (A-MAR) beginning in August 2015. These A-MAR are not supported by the
relatively stable
234
Th xs Inventories from late 2011 through August 2016 (Larson
et al. 2018) (Fig. 14.2) and therefore are not a reflection of increased sedimentation
rates, but are likely due to the re-establishment of bioturbation. Bioturbation mixes
234
Th xs downward, deepening the
234
Th xs profile downcore and falsely increasing
MARs (Larson et al. 2018). It is also unknown the reason(s) that bioturbation was
re-established at specific sites at different times. Site DSH10 was the exception as
234
Th xs MARs remained low through 2016 indicating low sedimentation rates and a
lack of bioturbation (Larson et al. 2018) (Fig. 14.2). Whether bioturbation was
never present at DSH10 (pre-event) or if this site remains in transition and/or has not
recovered from the depositional pulse is unknown. The lack of bioturbation at site
DSH10 increases the preservation potential of the depositional pulse at site DSH10
(Fig. 14.2). Alternatively, the return of bioturbation at sites DSH08, PCB06, and
M04 decreases the preservation potential of the depositional pulse depending on if
the depositional pulse layer is buried below the depth of bioturbation (Fig. 14.2).
The silt content continues to become more consistent/stable and similar to preevent values in 2013–2016 cores as compared to the 2010–2011 event signature.
This reinforces the time-sensitive nature of using % silt as an indicator of MOSSFA
as it does not appear to be well preserved and/or detectable in the sedimentary
record. In contrast,
210
Pb xs dating continues to progressively resolve the depositional
pulse beginning in the 2012 collections through the 2016 collections (Larson et al.
2018) (Fig. 14.3) with sequential intervals of similar activity capped by increases in
activity from post-event deposition (Larson et al. 2018).
14.6 Preservation Potential in the Sedimentary Record
From a sedimentological perspective, the potential for preservation of deposited
oil- contaminated sediments associated with the DWH event, and their detection in
the sedimentary record, is dependent on a variety of factors including (1) bioturbation/mixing, (2) burial, (3) degradation of the signature, (4) sediment compaction,
and (5) remobilization, transport, and secondary deposition (Fig. 14.2). The presence of bioturbation and mixing will decrease the potential for preservation/
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…
14.5 Stabilization/Recovery: Post-event (2013–2016)
Beginning ~3 years after the DWH blowout and associated depositional pulse, there
were indications of variability in the evolution of the sedimentary system as it stabilized/recovered. At the time-series sites collected between 2013 and 2016, lower
234
Th xs Inventories did remain consistent with the postdepositional pulse Inventories
for 2011 and 2012 indicating continued lower rates of sedimentation (Fig. 14.2).
The
234
Th xs MARs exhibited specific increases at different collection years. Site
DSH08 exhibited an apparent increase in
234
Th xs MAR (A-MAR) beginning in
August 2013, while sites M04 and PCB06 recorded apparent increases in
234
Th xs
MAR (A-MAR) beginning in August 2015. These A-MAR are not supported by the
relatively stable
234
Th xs Inventories from late 2011 through August 2016 (Larson
et al. 2018) (Fig. 14.2) and therefore are not a reflection of increased sedimentation
rates, but are likely due to the re-establishment of bioturbation. Bioturbation mixes
234
Th xs downward, deepening the
234
Th xs profile downcore and falsely increasing
MARs (Larson et al. 2018). It is also unknown the reason(s) that bioturbation was
re-established at specific sites at different times. Site DSH10 was the exception as
234
Th xs MARs remained low through 2016 indicating low sedimentation rates and a
lack of bioturbation (Larson et al. 2018) (Fig. 14.2). Whether bioturbation was
never present at DSH10 (pre-event) or if this site remains in transition and/or has not
recovered from the depositional pulse is unknown. The lack of bioturbation at site
DSH10 increases the preservation potential of the depositional pulse at site DSH10
(Fig. 14.2). Alternatively, the return of bioturbation at sites DSH08, PCB06, and
M04 decreases the preservation potential of the depositional pulse depending on if
the depositional pulse layer is buried below the depth of bioturbation (Fig. 14.2).
The silt content continues to become more consistent/stable and similar to preevent values in 2013–2016 cores as compared to the 2010–2011 event signature.
This reinforces the time-sensitive nature of using % silt as an indicator of MOSSFA
as it does not appear to be well preserved and/or detectable in the sedimentary
record. In contrast,
210
Pb xs dating continues to progressively resolve the depositional
pulse beginning in the 2012 collections through the 2016 collections (Larson et al.
2018) (Fig. 14.3) with sequential intervals of similar activity capped by increases in
activity from post-event deposition (Larson et al. 2018).
14.6 Preservation Potential in the Sedimentary Record
From a sedimentological perspective, the potential for preservation of deposited
oil- contaminated sediments associated with the DWH event, and their detection in
the sedimentary record, is dependent on a variety of factors including (1) bioturbation/mixing, (2) burial, (3) degradation of the signature, (4) sediment compaction,
and (5) remobilization, transport, and secondary deposition (Fig. 14.2). The presence of bioturbation and mixing will decrease the potential for preservation/
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…