279
16.3.5.2 Post-impact: Ecological Consequences – Benthic Foraminiferal
Resilience
Following the decrease in abundance after the DWH event, the diversity of benthic
foraminifera at impacted sites increased from 2011 to 2013 and plateaued from
2013 to 2015 (Schwing et al. 2018a; Schwing and Machain Castillo 2020). This is
the same time frame as the return to steady-state conditions seen in redox-sensitive
elements Re and Mn.
16.3.6 Thirty Years After Ixtoc 1: What Do Redox-Sensitive
Metals Reveal?
Thirty years before the Deepwater Horizon event, another major submarine blowout of 130 million gallons of crude oil occurred in the Bay of Campeche of the
Gulf of Mexico in 1979–1980. The events were similar in many aspects (Schwing
et al. 2020), including the massive accidental release of crude oil in the water column, followed by the application of million gallons of dispersant. The three
decades between the two blowouts allow us to compare the two events, assess the
fate of the oil, and estimate the possible long-term impacts and implications of the
DWH spill.
This earlier spill allows us to test the hypothesis that the large sedimentation
pulse which was a consequence of the 2010 blowout is not unique to the DWH event
and also occurred following the blowout at Ixtoc 1. In July 2015, we sampled sites
near the wellhead where the blowout occurred, and west and northwest of the wellhead where the crude oil drifted. The same sampling approach and analytical methods were used to determine redox-sensitive metals in sediments. Pore water oxygen
was measured in situ with an optode fiber microsensor.
At the shallowest site located at the wellhead (Ixtoc 1, 60 m depth), Mn is reduced
at the surface, with an oxygen penetration depth of 1 mm, virtually at the sedimentwater interface (Fig. 16.5a). This is expected given the relatively shallow water
depth and high-sedimentation rate. No Mn(IV) oxide exists. At IXW 500 (1200 m
water depth), IXN 500 (1240 m), and IXNW 750 (2043 m) multiple Mn oxide peaks
are present (Fig. 16.5b, c, d), which is consistent with a shoaled redoxcline following a MOSSFA event similar to the one observed and documented after the DWH
blowout.
These Mn profiles document nonsteady-state behavior in both NGoM and sites
near Ixtoc 1, consistent with the hypothesis that MOSSFA events, with a large pulse
of organic-rich material, are not unique to the DWH event and may occur in many
spills of this type.
16 Changes in Redox Conditions of Surface Sediments Following the Deepwater…
16.3.5.2 Post-impact: Ecological Consequences – Benthic Foraminiferal
Resilience
Following the decrease in abundance after the DWH event, the diversity of benthic
foraminifera at impacted sites increased from 2011 to 2013 and plateaued from
2013 to 2015 (Schwing et al. 2018a; Schwing and Machain Castillo 2020). This is
the same time frame as the return to steady-state conditions seen in redox-sensitive
elements Re and Mn.
16.3.6 Thirty Years After Ixtoc 1: What Do Redox-Sensitive
Metals Reveal?
Thirty years before the Deepwater Horizon event, another major submarine blowout of 130 million gallons of crude oil occurred in the Bay of Campeche of the
Gulf of Mexico in 1979–1980. The events were similar in many aspects (Schwing
et al. 2020), including the massive accidental release of crude oil in the water column, followed by the application of million gallons of dispersant. The three
decades between the two blowouts allow us to compare the two events, assess the
fate of the oil, and estimate the possible long-term impacts and implications of the
DWH spill.
This earlier spill allows us to test the hypothesis that the large sedimentation
pulse which was a consequence of the 2010 blowout is not unique to the DWH event
and also occurred following the blowout at Ixtoc 1. In July 2015, we sampled sites
near the wellhead where the blowout occurred, and west and northwest of the wellhead where the crude oil drifted. The same sampling approach and analytical methods were used to determine redox-sensitive metals in sediments. Pore water oxygen
was measured in situ with an optode fiber microsensor.
At the shallowest site located at the wellhead (Ixtoc 1, 60 m depth), Mn is reduced
at the surface, with an oxygen penetration depth of 1 mm, virtually at the sedimentwater interface (Fig. 16.5a). This is expected given the relatively shallow water
depth and high-sedimentation rate. No Mn(IV) oxide exists. At IXW 500 (1200 m
water depth), IXN 500 (1240 m), and IXNW 750 (2043 m) multiple Mn oxide peaks
are present (Fig. 16.5b, c, d), which is consistent with a shoaled redoxcline following a MOSSFA event similar to the one observed and documented after the DWH
blowout.
These Mn profiles document nonsteady-state behavior in both NGoM and sites
near Ixtoc 1, consistent with the hypothesis that MOSSFA events, with a large pulse
of organic-rich material, are not unique to the DWH event and may occur in many
spills of this type.
16 Changes in Redox Conditions of Surface Sediments Following the Deepwater…