241
oil-contaminated sediments and specifically isolate DWH oil contamination and is
described by Romero et al. (2020). Inorganic impacts and sedimentary signatures
can include shifts in redox geochemistry as described by Hastings et al. (2020).
Biological indicators of oil-contaminated sedimentation and benthic impacts also
include benthic foraminifera by Schwing et al. (2020) and macrofaunal by Montagna
et al. (2020).
14.3 Sedimentary Response: Depositional Pulse (2010–2011)
The sedimentary response of the DWH event was manifested in sediment cores collected in the Fall of 2010 through early 2011 as increased rates of sedimentation and
subtle changes in sedimentology at the time-series sites (DSH08, DSH10, PCB06,
M04). This depositional pulse associated with MOSSFA was characterized by high
234
Th xs Inventories and high
234
Th xs MAR, indicating high sedimentation, over the
surficial 10–20 mm (Fig. 14.2). Downcore
210
Pb xs geochronologies recorded MAR
an order of magnitude lower than surficial rates based on
234
Th xs (Brooks et al.
2015). However, rates calculated by different methods representing different time
frames cannot be directly compared due to the differences in time scales involved,
which is commonly referred to as the Sadler effect (Sadler 1981). Where
234
Th xs
represents monthly time-scale sedimentation,
210
Pb xs is more reflective of annual- to
decadal-scale sediment accumulation. This leads to a consistently higher estimation
of MAR by
234
Th xs as compared to
210
Pb xs (Sadler 1981) and provides evidence to
support the importance of comparisons using the same chronometer. As there were
no pre-event
234
Th xs data available for direct comparison, the high
234
Th xs Inventory
and MAR measured in 2010 and early 2011, associated with the depositional pulse,
initially could not be confirmed (Brooks et al. 2015). The continued measurement
of
234
Th xs Inventory and MAR over the 6-year time series allowed for the confirmation of the depositional pulse and evaluation of sedimentation (Inventory and MAR)
and bioturbation (A-MAR) as the sedimentary system evolved following the DWH
event.
There were no major systematic changes in sedimentological parameters over
the 10–20 mm-thick pulse layer as compared to underlying sediments, the exception
to this being silt content (% silt), which exhibited major excursions in the surfaces
of the time-series cores collected in late 2010 and early 2011 (Fig. 14.3). The % silt
increased dramatically in some cores and decreased dramatically in others as compared to consistent downcore (pre-event) values, suggesting a deviation in sedimentation processes during 2010 and 2011 concurrent with the depositional pulse
(Brooks et al. 2015). Below the surficial 10–20 mm (i.e., the depositional pulse
layer), silt content did not vary, indicating reproducibility of high-resolution analyses and little spatial heterogeneity and suggesting a relatively stable sedimentological regime for >100 years preceding the depositional pulse (Larson et al. 2018).
Composition, as represented by carbonate content (%carbonate), showed no systematic or detectable changes within the surficial 10–20 mm of the time-series cores
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…
oil-contaminated sediments and specifically isolate DWH oil contamination and is
described by Romero et al. (2020). Inorganic impacts and sedimentary signatures
can include shifts in redox geochemistry as described by Hastings et al. (2020).
Biological indicators of oil-contaminated sedimentation and benthic impacts also
include benthic foraminifera by Schwing et al. (2020) and macrofaunal by Montagna
et al. (2020).
14.3 Sedimentary Response: Depositional Pulse (2010–2011)
The sedimentary response of the DWH event was manifested in sediment cores collected in the Fall of 2010 through early 2011 as increased rates of sedimentation and
subtle changes in sedimentology at the time-series sites (DSH08, DSH10, PCB06,
M04). This depositional pulse associated with MOSSFA was characterized by high
234
Th xs Inventories and high
234
Th xs MAR, indicating high sedimentation, over the
surficial 10–20 mm (Fig. 14.2). Downcore
210
Pb xs geochronologies recorded MAR
an order of magnitude lower than surficial rates based on
234
Th xs (Brooks et al.
2015). However, rates calculated by different methods representing different time
frames cannot be directly compared due to the differences in time scales involved,
which is commonly referred to as the Sadler effect (Sadler 1981). Where
234
Th xs
represents monthly time-scale sedimentation,
210
Pb xs is more reflective of annual- to
decadal-scale sediment accumulation. This leads to a consistently higher estimation
of MAR by
234
Th xs as compared to
210
Pb xs (Sadler 1981) and provides evidence to
support the importance of comparisons using the same chronometer. As there were
no pre-event
234
Th xs data available for direct comparison, the high
234
Th xs Inventory
and MAR measured in 2010 and early 2011, associated with the depositional pulse,
initially could not be confirmed (Brooks et al. 2015). The continued measurement
of
234
Th xs Inventory and MAR over the 6-year time series allowed for the confirmation of the depositional pulse and evaluation of sedimentation (Inventory and MAR)
and bioturbation (A-MAR) as the sedimentary system evolved following the DWH
event.
There were no major systematic changes in sedimentological parameters over
the 10–20 mm-thick pulse layer as compared to underlying sediments, the exception
to this being silt content (% silt), which exhibited major excursions in the surfaces
of the time-series cores collected in late 2010 and early 2011 (Fig. 14.3). The % silt
increased dramatically in some cores and decreased dramatically in others as compared to consistent downcore (pre-event) values, suggesting a deviation in sedimentation processes during 2010 and 2011 concurrent with the depositional pulse
(Brooks et al. 2015). Below the surficial 10–20 mm (i.e., the depositional pulse
layer), silt content did not vary, indicating reproducibility of high-resolution analyses and little spatial heterogeneity and suggesting a relatively stable sedimentological regime for >100 years preceding the depositional pulse (Larson et al. 2018).
Composition, as represented by carbonate content (%carbonate), showed no systematic or detectable changes within the surficial 10–20 mm of the time-series cores
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…