377
intensification of reducing conditions and 2–3-fold increase in sedimentary PAH
concentrations resulting from the MOSSFA event. Benthic foraminifera in the preDWH intervals (>10 mm) resembled assemblages from previous studies relating
specific benthic foraminifera assemblages and to Caribbean Midwater mass (Denne
and Sen Gupta 1991) and characterizing dominant species in continental slope sediments (Culver and Buzas 1983; Osterman 2003).
A modest (0.2–0.4‰) but persistent δ
13
C CaCO3 depletion in Cibicidoides spp.
(Cibicidoides wuellerstorfi and Cibicidoides pachyderma) extracted from DWH
intervals of impacted sites was observed in 2010 and early 2011 (Fig. 23.1; Schwing
et al. 2018a). The depletion was significantly beyond any natural (pre-DWH, background) variability and demonstrated that benthic foraminiferal calcite recorded the
depositional event. The stable carbon composition of benthic foraminiferal calcite
(δ
13
C CaCO3 ) is affected by environmental changes to bottom water δ
13
C of dissolved
inorganic carbon (DIC), the carbon isotopic composition of food sources (e.g.,
microbial biomass, phytodetritus), and the flux of total organic carbon (TOC)
(Rathburn et al. 2003; Torres 2003; Hill et al. 2004; Nomaki et al. 2006; Panieri
2006; Panieri and Sen Gupta 2008; Zariess and Mackensen 2011; Panieri et al.
2014; Theodor et al. 2016). Zariess and Mackensen (2011) found that seasonal
increases in phytodetritus deposition caused depletion in Cibicidoides wuellerstorfi
δ
13
C CaCO3 from 0.1‰ to 0.4‰. The relationship between δ
13
C CaCO3 and TOC flux is
based on increased microbial respiration rates, which in turn depletes the δ
13
C of
dissolved inorganic carbon of bottom water. This relationship suggests that increased
TOC flux could result in δ
13
C CaCO3 depletion following the DWH event because of
increased sedimentary mass accumulation rates (up to 4–10-fold; Brooks et al.
2015) and total organic carbon (TOC) flux (Romero et al. 2015; Schwing et al.
2015) caused by MOSSFA.
23.2.3 Response
Initial signs of benthic foraminiferal response were observed at two sites in the
northern GoM in as short as 2 years after the DWH event, but the authors concluded
that further work was needed to determine the full spatial extent and time frame of
recovery (Schwing et al. 2017b). The response varied at each site. There was a protracted return to pre-DWH values with respect to density (at least 2 years) and a
rapid (~1 year) return to pre-DWH diversity values at the site PCB06. However,
there was a relatively fast return to pre-DWH values for density (~1 year) and a
prolonged return to pre-DWH diversity values (at least 2 years) at site DSH08.
Opportunistic taxa, which are able to tolerate high organic carbon deposition and
petroleum concentration, were likely dominant in the areas with a rapid return to
pre-DWH density values and a protracted return to pre-DWH diversity values. The
benthic foraminifera response to the increased petroleum concentration and
enhanced reducing conditions suggested that the benthic resilience, following an
event such as the DWH, took on the order of 1–2 years to initiate (Schwing et al.
23 Impact and Resilience of Benthic Foraminifera in the Aftermath of the Deepwater…
intensification of reducing conditions and 2–3-fold increase in sedimentary PAH
concentrations resulting from the MOSSFA event. Benthic foraminifera in the preDWH intervals (>10 mm) resembled assemblages from previous studies relating
specific benthic foraminifera assemblages and to Caribbean Midwater mass (Denne
and Sen Gupta 1991) and characterizing dominant species in continental slope sediments (Culver and Buzas 1983; Osterman 2003).
A modest (0.2–0.4‰) but persistent δ
13
C CaCO3 depletion in Cibicidoides spp.
(Cibicidoides wuellerstorfi and Cibicidoides pachyderma) extracted from DWH
intervals of impacted sites was observed in 2010 and early 2011 (Fig. 23.1; Schwing
et al. 2018a). The depletion was significantly beyond any natural (pre-DWH, background) variability and demonstrated that benthic foraminiferal calcite recorded the
depositional event. The stable carbon composition of benthic foraminiferal calcite
(δ
13
C CaCO3 ) is affected by environmental changes to bottom water δ
13
C of dissolved
inorganic carbon (DIC), the carbon isotopic composition of food sources (e.g.,
microbial biomass, phytodetritus), and the flux of total organic carbon (TOC)
(Rathburn et al. 2003; Torres 2003; Hill et al. 2004; Nomaki et al. 2006; Panieri
2006; Panieri and Sen Gupta 2008; Zariess and Mackensen 2011; Panieri et al.
2014; Theodor et al. 2016). Zariess and Mackensen (2011) found that seasonal
increases in phytodetritus deposition caused depletion in Cibicidoides wuellerstorfi
δ
13
C CaCO3 from 0.1‰ to 0.4‰. The relationship between δ
13
C CaCO3 and TOC flux is
based on increased microbial respiration rates, which in turn depletes the δ
13
C of
dissolved inorganic carbon of bottom water. This relationship suggests that increased
TOC flux could result in δ
13
C CaCO3 depletion following the DWH event because of
increased sedimentary mass accumulation rates (up to 4–10-fold; Brooks et al.
2015) and total organic carbon (TOC) flux (Romero et al. 2015; Schwing et al.
2015) caused by MOSSFA.
23.2.3 Response
Initial signs of benthic foraminiferal response were observed at two sites in the
northern GoM in as short as 2 years after the DWH event, but the authors concluded
that further work was needed to determine the full spatial extent and time frame of
recovery (Schwing et al. 2017b). The response varied at each site. There was a protracted return to pre-DWH values with respect to density (at least 2 years) and a
rapid (~1 year) return to pre-DWH diversity values at the site PCB06. However,
there was a relatively fast return to pre-DWH values for density (~1 year) and a
prolonged return to pre-DWH diversity values (at least 2 years) at site DSH08.
Opportunistic taxa, which are able to tolerate high organic carbon deposition and
petroleum concentration, were likely dominant in the areas with a rapid return to
pre-DWH density values and a protracted return to pre-DWH diversity values. The
benthic foraminifera response to the increased petroleum concentration and
enhanced reducing conditions suggested that the benthic resilience, following an
event such as the DWH, took on the order of 1–2 years to initiate (Schwing et al.
23 Impact and Resilience of Benthic Foraminifera in the Aftermath of the Deepwater…