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16.3.5 Post-impact: Ecological Consequences – Benthic
Foraminifera
Downcore changes in Mn and Re reveal clear evidence of changes in redox conditions following the event. What is the ecological impact of such changes on the
benthic community? Given that redox changes occurred at the mm scale, benthic
foraminifera are potentially sensitive indicators of changes in reducing conditions.
We have documented changes in density of benthic foraminifera at two sites, DSH08
and PCB06, in December 2010 and February 2011 (Schwing et al. 2015; Schwing
and Machain Castillo 2020). Where Mn and Re indicate significant reducing conditions by Mn depletion and Re enrichment, there is a clear decrease in density of the
dominant genera of benthic foraminifera (Hastings et al. 2016; Schwing et al. 2015).
At site DSH08 in December 2010, a 40–60% reduction in both Bulimina spp.
and Uvigerina spp., the most abundant genera of benthic foraminifera, occurs
between 13 and 17 mm. This is coincident with the Mn minimum and a modest
(0.20 ppb; 35%) Re enrichment (Hastings et al. 2016). At the surface, a significant
decrease in density of benthic foraminifera occurs, while a modest (0.16 ppb; 30%)
Re increase and Mn minimum occurs, consistent with more reducing conditions. On
the subsequent sampling date, February 2011, a dramatic reduction in the most
abundant genera, Bulimina spp. and Uvigerina spp., occurs at 13 mm, coincident
with the Mn minimum and a 0.14 ppb increase in Re (Hastings et al. 2016). A similarly large reduction in Brizalina spp. and Bolivina spp. also occurs at this depth
(Schwing et al. 2015). Site PCB06 in December 2010 and February 2011 reveals a
similar relationship between redox-sensitive metals and benthic foraminiferal density: a significant and substantial decrease in density of the three dominant genera
occurs when both Mn and Re indicate reducing conditions. While reducing conditions can explain these changes, polycyclic aromatic hydrocarbons (PAHs) and
other toxic organic compounds found in crude oil may be another reason for the
changes in foraminiferal density.
16.3.5.1 Post-impact: Ecological Consequences – Benthic Foraminifera
(C-13 Depletion)
A modest but persistent depletion in the stable carbon isotope composition of benthic foraminiferal calcite extracted from impacted sites was observed in 2010 and
early 2011 (Schwing et al. 2018b; Schwing and Machain Castillo 2020). The depletion was likely caused by intensifying reducing conditions brought about by
increased microbial respiration of marine oil snow. Benthic foraminiferal carbon
isotope composition took about 3 years to return to steady state, which corresponds
to less intense reducing conditions, and the steady state achieved in Re and Mn
concentrations we observe during the same time frame.
D. W. Hastings et al.
16.3.5 Post-impact: Ecological Consequences – Benthic
Foraminifera
Downcore changes in Mn and Re reveal clear evidence of changes in redox conditions following the event. What is the ecological impact of such changes on the
benthic community? Given that redox changes occurred at the mm scale, benthic
foraminifera are potentially sensitive indicators of changes in reducing conditions.
We have documented changes in density of benthic foraminifera at two sites, DSH08
and PCB06, in December 2010 and February 2011 (Schwing et al. 2015; Schwing
and Machain Castillo 2020). Where Mn and Re indicate significant reducing conditions by Mn depletion and Re enrichment, there is a clear decrease in density of the
dominant genera of benthic foraminifera (Hastings et al. 2016; Schwing et al. 2015).
At site DSH08 in December 2010, a 40–60% reduction in both Bulimina spp.
and Uvigerina spp., the most abundant genera of benthic foraminifera, occurs
between 13 and 17 mm. This is coincident with the Mn minimum and a modest
(0.20 ppb; 35%) Re enrichment (Hastings et al. 2016). At the surface, a significant
decrease in density of benthic foraminifera occurs, while a modest (0.16 ppb; 30%)
Re increase and Mn minimum occurs, consistent with more reducing conditions. On
the subsequent sampling date, February 2011, a dramatic reduction in the most
abundant genera, Bulimina spp. and Uvigerina spp., occurs at 13 mm, coincident
with the Mn minimum and a 0.14 ppb increase in Re (Hastings et al. 2016). A similarly large reduction in Brizalina spp. and Bolivina spp. also occurs at this depth
(Schwing et al. 2015). Site PCB06 in December 2010 and February 2011 reveals a
similar relationship between redox-sensitive metals and benthic foraminiferal density: a significant and substantial decrease in density of the three dominant genera
occurs when both Mn and Re indicate reducing conditions. While reducing conditions can explain these changes, polycyclic aromatic hydrocarbons (PAHs) and
other toxic organic compounds found in crude oil may be another reason for the
changes in foraminiferal density.
16.3.5.1 Post-impact: Ecological Consequences – Benthic Foraminifera
(C-13 Depletion)
A modest but persistent depletion in the stable carbon isotope composition of benthic foraminiferal calcite extracted from impacted sites was observed in 2010 and
early 2011 (Schwing et al. 2018b; Schwing and Machain Castillo 2020). The depletion was likely caused by intensifying reducing conditions brought about by
increased microbial respiration of marine oil snow. Benthic foraminiferal carbon
isotope composition took about 3 years to return to steady state, which corresponds
to less intense reducing conditions, and the steady state achieved in Re and Mn
concentrations we observe during the same time frame.
D. W. Hastings et al.