244
(Brooks et al. 2015). This indicates no detectable changes in sediment source(s) for
the siliciclastic or carbonate regions of the study area during the event. This is due
to MOSSFA stripping the overlying water column of particulates that would have
eventually settled to the seafloor in each of the two sediment regimes, so composition may not be expected to change measurably even though the rate of sedimentation increased (Brooks et al. 2015; Chanton et al. 2014; Romero et al. 2015; Romero
et al. 2017; Schwing et al. 2017).
Detection of the depositional pulse within a 4–5-month period that resulted in a
10–20 mm thick sediment layer required the unconventional use of
234
Th xs as a geochronological tool. This was due to the exceptionally high (2 mm)-resolution sampling, the high sedimentation rate for detection of
234
Th xs profiles to determine
Inventories and MAR, as well as the interruption of bioturbation by the event allowing for detection of the depositional pulse by
234
Th xs and % silt (Brooks et al. 2015)
(Figs. 14.2 and 14.3).
14.4 Initial Sedimentary Response: Post-event (2011–2012)
In the immediate years following the depositional pulse, a decrease in sedimentation was indicated by cores collected in September 2011 and 2012 at all of the timeseries sites. This is expressed as lower
234
Th xs Inventories and lower
234
Th xs MARs
as compared to the depositional pulse (Larson et al. 2018) (Fig. 14.2). As these
Inventories and MARs are based upon the same chronometer (
234
Th xs ), they are
directly comparable to those associated with the depositional pulse. This also serves
as initial baseline information indicating that the sedimentation rates of the depositional pulse were high. The low
234
Th xs Inventory and low
234
Th xs MAR also indicate
a lack of bioturbation at all of the time-series sites for the first few years following
the depositional pulse and possible lack of recovery of the benthic ecosystem over
this period.
Sedimentologically, the subtle diagnostic indicator (% silt) of the depositional
pulse was not as detectable in cores collected in 2011 and 2012 as compared to
those collected in 2010 (Fig. 14.3). Most cores exhibited a stabilization in % silt
toward pre-event (downcore) values. This may be an indication that % silt is not a
strong diagnostic indicator of MOSSFA in sedimentary records, potentially due to
challenges in detecting changes in % silt, and/or preservation (Fig. 14.2).
Time-series cores collected in August 2012 showed that the 2010 depositional
pulse began to be resolved by
210
Pb xs (half-life ~22.3 years) in little more than
2 years following the event (Fig. 14.3).
210
Pb xs profiles began to reflect several adjacent depth intervals with similar
210
Pb xs activities (dpm/g), indicating intervals were
of approximately the same age and deposited at the same time (Larson et al. 2018).
In the surface intervals of cores collected in 2010, the
210
Pb xs profile is more exponential in shape, lacking intervals with similar activities (dpm/g) illustrating the
ineffectiveness of
210
Pb xs to resolve the depositional pulse.
R. A. Larson et al.
(Brooks et al. 2015). This indicates no detectable changes in sediment source(s) for
the siliciclastic or carbonate regions of the study area during the event. This is due
to MOSSFA stripping the overlying water column of particulates that would have
eventually settled to the seafloor in each of the two sediment regimes, so composition may not be expected to change measurably even though the rate of sedimentation increased (Brooks et al. 2015; Chanton et al. 2014; Romero et al. 2015; Romero
et al. 2017; Schwing et al. 2017).
Detection of the depositional pulse within a 4–5-month period that resulted in a
10–20 mm thick sediment layer required the unconventional use of
234
Th xs as a geochronological tool. This was due to the exceptionally high (2 mm)-resolution sampling, the high sedimentation rate for detection of
234
Th xs profiles to determine
Inventories and MAR, as well as the interruption of bioturbation by the event allowing for detection of the depositional pulse by
234
Th xs and % silt (Brooks et al. 2015)
(Figs. 14.2 and 14.3).
14.4 Initial Sedimentary Response: Post-event (2011–2012)
In the immediate years following the depositional pulse, a decrease in sedimentation was indicated by cores collected in September 2011 and 2012 at all of the timeseries sites. This is expressed as lower
234
Th xs Inventories and lower
234
Th xs MARs
as compared to the depositional pulse (Larson et al. 2018) (Fig. 14.2). As these
Inventories and MARs are based upon the same chronometer (
234
Th xs ), they are
directly comparable to those associated with the depositional pulse. This also serves
as initial baseline information indicating that the sedimentation rates of the depositional pulse were high. The low
234
Th xs Inventory and low
234
Th xs MAR also indicate
a lack of bioturbation at all of the time-series sites for the first few years following
the depositional pulse and possible lack of recovery of the benthic ecosystem over
this period.
Sedimentologically, the subtle diagnostic indicator (% silt) of the depositional
pulse was not as detectable in cores collected in 2011 and 2012 as compared to
those collected in 2010 (Fig. 14.3). Most cores exhibited a stabilization in % silt
toward pre-event (downcore) values. This may be an indication that % silt is not a
strong diagnostic indicator of MOSSFA in sedimentary records, potentially due to
challenges in detecting changes in % silt, and/or preservation (Fig. 14.2).
Time-series cores collected in August 2012 showed that the 2010 depositional
pulse began to be resolved by
210
Pb xs (half-life ~22.3 years) in little more than
2 years following the event (Fig. 14.3).
210
Pb xs profiles began to reflect several adjacent depth intervals with similar
210
Pb xs activities (dpm/g), indicating intervals were
of approximately the same age and deposited at the same time (Larson et al. 2018).
In the surface intervals of cores collected in 2010, the
210
Pb xs profile is more exponential in shape, lacking intervals with similar activities (dpm/g) illustrating the
ineffectiveness of
210
Pb xs to resolve the depositional pulse.
R. A. Larson et al.