240
strongly adsorbs onto particles producing a flux of
234
Th xs to the seafloor associated
with sedimentation (Winkler and Rosner 2000).
234
Th xs has a short half-life of
~24 days and is usually only detectable in surficial sediments representing sedimentation and/or bioturbation. Due to the short (~24 day) half-life,
234
Th xs has traditionally been used to determine the depth of bioturbation (McClintic et al. 2008; Pope
et al. 1996; Yeager et al. 2004), but under certain conditions (high sedimentation,
high sampling resolution, stratigraphic integrity), it may be used as a chronological
tool (Brooks et al. 2015). Activities of
234
Th xs were decay corrected (DC
234
Th xs ) for
activity lost due to decay between the time of core collection and sample analysis,
and data are expressed as Inventories and as mass accumulation rates (MAR)
(Brooks et al. 2015; Larson et al. 2018).
234
Th xs Inventory is the sum of activity in a
core, which is an indicator of the flux of
234
Th xs to the seafloor associated with sedimentation and is not influenced by bioturbation (Brooks et al. 2015).
234
Th xs MAR
is a function of the
234
Th xs activity in a sediment core, as well as the depth downcore
of the
234
Th xs profile, and can be influenced by both sedimentation and bioturbation
(downcore mixing deepening the
234
Th xs profile). By utilizing the
234
Th xs Inventory
as a measure of sedimentation, the
234
Th xs MAR can be used as an indicator of bioturbation/mixing in surficial sediments. Specifically, high Inventory with a high
MAR indicates high sedimentation, and low Inventory with a low MAR indicates
low sedimentation. The combination of a low Inventory with a high MAR indicates
low sedimentation with the influence of bioturbation/mixing. Under these conditions, MAR is not an accurate indicator of sedimentation/accumulation due to the
influence of bioturbation and is referred to as apparent MAR (A-MAR).
With a 22.3-year half-life,
210
Pb xs provides age control and sedimentation rates
over the past ~120 years but is less sensitive to monthly time scales (Chisté and Bé
2007; Appleby 2001). Therefore,
210
Pb xs age dating is not as useful immediately following an event but becomes more useful as the primary dating tool in years to
decades following a sedimentation event. The constant rate of supply (CRS) model,
which is appropriate under conditions of varying accumulation rates, is used to
provide
210
Pb xs age dating for pre-event downcore baselines and to detect the sedimentation pulse in subsequent years (2012–2016) (Appleby 2001; Binford 1990;
Appleby and Oldfield 1983).
14.2.3 Sediment Texture and Composition
Sediment texture and composition analyses were conducted on extruded samples
and included grain size by methodology described by Folk (1965) and calcium carbonate content (%CaCO 3 ) by methodology by Milliman (1974) to determine variability in sediment sources and depositional mechanisms. Grain size is presented as
% silt as this was the most indicative of changes in sediment texture (Larson et al.
2018). There are multiple indicators of oil-contaminated sediments and the benthic
impacts including organic and inorganic geochemical indicators and biological
responses. Organic geochemical fingerprinting is utilized to identify
R. A. Larson et al.
strongly adsorbs onto particles producing a flux of
234
Th xs to the seafloor associated
with sedimentation (Winkler and Rosner 2000).
234
Th xs has a short half-life of
~24 days and is usually only detectable in surficial sediments representing sedimentation and/or bioturbation. Due to the short (~24 day) half-life,
234
Th xs has traditionally been used to determine the depth of bioturbation (McClintic et al. 2008; Pope
et al. 1996; Yeager et al. 2004), but under certain conditions (high sedimentation,
high sampling resolution, stratigraphic integrity), it may be used as a chronological
tool (Brooks et al. 2015). Activities of
234
Th xs were decay corrected (DC
234
Th xs ) for
activity lost due to decay between the time of core collection and sample analysis,
and data are expressed as Inventories and as mass accumulation rates (MAR)
(Brooks et al. 2015; Larson et al. 2018).
234
Th xs Inventory is the sum of activity in a
core, which is an indicator of the flux of
234
Th xs to the seafloor associated with sedimentation and is not influenced by bioturbation (Brooks et al. 2015).
234
Th xs MAR
is a function of the
234
Th xs activity in a sediment core, as well as the depth downcore
of the
234
Th xs profile, and can be influenced by both sedimentation and bioturbation
(downcore mixing deepening the
234
Th xs profile). By utilizing the
234
Th xs Inventory
as a measure of sedimentation, the
234
Th xs MAR can be used as an indicator of bioturbation/mixing in surficial sediments. Specifically, high Inventory with a high
MAR indicates high sedimentation, and low Inventory with a low MAR indicates
low sedimentation. The combination of a low Inventory with a high MAR indicates
low sedimentation with the influence of bioturbation/mixing. Under these conditions, MAR is not an accurate indicator of sedimentation/accumulation due to the
influence of bioturbation and is referred to as apparent MAR (A-MAR).
With a 22.3-year half-life,
210
Pb xs provides age control and sedimentation rates
over the past ~120 years but is less sensitive to monthly time scales (Chisté and Bé
2007; Appleby 2001). Therefore,
210
Pb xs age dating is not as useful immediately following an event but becomes more useful as the primary dating tool in years to
decades following a sedimentation event. The constant rate of supply (CRS) model,
which is appropriate under conditions of varying accumulation rates, is used to
provide
210
Pb xs age dating for pre-event downcore baselines and to detect the sedimentation pulse in subsequent years (2012–2016) (Appleby 2001; Binford 1990;
Appleby and Oldfield 1983).
14.2.3 Sediment Texture and Composition
Sediment texture and composition analyses were conducted on extruded samples
and included grain size by methodology described by Folk (1965) and calcium carbonate content (%CaCO 3 ) by methodology by Milliman (1974) to determine variability in sediment sources and depositional mechanisms. Grain size is presented as
% silt as this was the most indicative of changes in sediment texture (Larson et al.
2018). There are multiple indicators of oil-contaminated sediments and the benthic
impacts including organic and inorganic geochemical indicators and biological
responses. Organic geochemical fingerprinting is utilized to identify
R. A. Larson et al.