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An ocean of oil…Rapid sedimentation and accumulation at the seafloor in the aftermath of the Macondo
Blowout
Samantha Joye
Department of Marine Sciences
University of Georgia
Contributors:
Patricia Medeiros, Kimberley Hunter (U Georgia); Uta Passow (UCSB); Arne Diercks (U Mississippi); Vernon Asper (U Southern Mississippi); Joe Montoya (GA Tech); Andreas Teske, Tingting Yang (U North
Carolina); Claudia Benitez‐Nelson and Willard S. Moore (U South Carolina)
Emulsified oil on the surface
Hydrocarbon jet from BOPstack
Pre‐Macondo view of the fate of oil derived from a deepwater blowout
Peterson, Joye et al. 2012 BioScience
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Emulsified oil on the surface
Hydrocarbon jet from BOPstack
Post Macondo view – seafloor accumulation is significant
Peterson, Joye et al. 2012 BioScience
The day it started: Sept. 6, 2010
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• Biological emulsification and sinking of oil‐snow• Dispersant‐mediated coagulation and sinking
•Ash fall‐out and sinking**also drilling mud!
Multiple mechanisms: Vertical Sedimentation (Oil‐Snow Blizzard)
Atlas and Hazen 2010 ES&T
A view from beneath the surface
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Multiple mechanisms: Lateral Intersection (Toxic Bathtub Ring)
Figure from Atlas and Hazen 2010 ES&T
• Multiple “plume” layersthat eventually intersect with the continental slopeand contaminate sediments with plume‐derived oil, etc.
Aug 2010 example
• Discussion topic: to what extent is vertically sinking material laterally entrained along (plume) isopycnals and deposited subsequently at slope intersection points?
Evidence of Accumulation, July‐Dec 2010 Study Area
In 2010: 50 box cores (100 cores); 25 MUCs (145 cores); 3 ALVIN dives (70 cores)
May 2010
May 2010
streamers
dispersed?
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Is this recent sedimentation? What are the mechanism(s)?
streamers
Dispersed oil
Widespread in every direction – thickness of layer varied
Picture courtesy A. Teske
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Microbial production of “oil snow”After one day after roller table incubation After 21 days, massive streamers
of oily marine snow
See: Passow et al. 2012; Zeirvogel et al. 2012
Oil Sheen
At the seafloor….
K. Ziervogel
K. Ziervogel
Sedimentation rates in September 2010
Source: Joye et al. in prep; data from Uta Passow
Floating sediment traps (Uta Passow, Vernon Asper, and Arne Diercks)
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Sedimentation rates in September 2010
0.E+00
4.E+06
8.E+06
1.E+07
St 2 St 3 St 6 St 14 St 16 St 17 St 25 St 27
ag
g. #
m-2
d-1
0.0
0.4
0.8
1.2
1.6
DW
in g
m-2
d-1
0.06 mm
0.12 mm
0.24 mm
DW g/m 2̂ /d
Southern (control)transect
wellheadvicinity
Clear increase in organic sedimentation around the wellhead
Source: Joye et al. in prep; data from Uta Passow
Oil Snow at depth (NE of wellhead, Sept. 2010)
Large snow particle
Small snow streamers
300 m
450 m
800 m
Dense beam attenuation layer
streamers
Vernon Asper “Snow Cam”
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40 dpm cm‐2Sept. 2010
Excess Thorium 234(dpm cm‐2)
Data: Benitez‐Nelson & Moore
MC252
28
26
1718
30
20
Rapid Sedimentation: 234Th(typical excess 234Th ≈ 6 dpm cm‐2)
n.d.
24
22
b.d.l.
Source: Joye et al. in prep
TPH100 µg/g
Sept. 2010
TPH(Total Petroleum Hydrocarbons)
PAH (Polycyclic Aromatic Hydrocarbons)
MC252
28
26
1718
22
20
27
16
PAH2 µg/g
TPH and PAH deposition:
Background: 0.2 µg/gSeeps: 103‐104 of µg/g
Source: Joye et al. in prep
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MC252
2000 ppmSep 2010
Barium is a drilling mud tracer
Solid Phase Barium(background 500 ppm)
Source: Joye et al. in prep
MC252
0.5 µg/gMay 2010Sep 2010Nov 2010
(Terpanes + Hopanes + Steranes)
Top sediments
Source: Joye et al. in prep; data from Pat Medeiros
Petroleum Biomarkers
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MC252
0.5 µg/gMay 2010Sep 2010Nov 2010
Source: Joye et al. in prep; data from Pat Medeiros
(Terpanes + Hopanes + Steranes)
Sub‐surface sediments
Petroleum Biomarkers
MC252
1.5 µg/gMay 2010Sep 2010Nov 2010
n‐AlkanesTop sediments
2.8
2.0
2.0
2.8
1.3
1.2
Carbon Preference IndexCPI: C23‐37(odd)/C24‐38(even)
CPI ~ 1‐3 oilCPI > 3 biogenic
Source: Joye et al. in prep; data from Pat Medeiros
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Burning – an unexpected pathway to the bottom
0.8
September 2010
Pyrogenic Index (PAHs, top sediments)Wang et al. (1999) ES&T
MC252
28
26
1718
22
20
Source: Joye et al. in prep
15 µg/L
Elemental Carbon (Thermal‐optical method)MUC core overlying water
Pyrogenic Signatures
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MC252
5 nmol/cc/d
Microbial Activity(average SR rate in interval)
vs
28
26
1718
22
20
*natural seep ~ 100+
Source: Joye et al. in prep
Impacts: reduced microbial activity
Impacts: reduced diversity/abundance of benthic fauna
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Summary• Multiple mechanisms (biological, pyrogenic, dispersant) and seafloor “expressions” of weathered oil deposition
• The relative importance of burn residue vs. biological deposition vs. dispersant‐mediated deposition remains to be determined
• concentrations of TPH, PAH, petroleum biomarkers, and UCM were elevated above background, esp. within 40 miles; not natural seeps!!
• microbial activity reduced in these layers (reduced biomass, inhibition, toxicity…)
• filter feeding fauna at the seafloor was suffocated by thisunprecedented sedimentation event – how long it will takethese communities to recover is unknown.