202
Toxicity studies and numerical models were used to demonstrate habitat recovery
due to dispersion and biodegradation of the residual oil in these oil translocationbased studies (Lee et al. 2003b; Niu and Lee 2013).
The Deepwater Horizon (DwH) accident was the first oil spill in deep waters
where natural sediment and/or mineral particle concentrations are too low to cause
the formation of ubiquitous amounts of OPAs. Thus sedimentation of oil to depth
was not expected. However, significant amounts of oil were observed to accumulate
at the seafloor (e.g., Valentine et al. 2014; Chanton et al. 2015; Schwing et al. 2015;
Passow and Hetland 2016), resulting in the realization that marine snow can lead to
the vertical transport of large amounts of oil.
Significant sedimentation of hydrocarbons in association with phytoplankton
had already been observed about 30 years earlier in mesocosm studies (Lee and
Anderson 1977; Lee et al. 1978, 1985), but sorption and active uptake of oil compounds were considered the main causes (Lee et al. 1978), although whole oil droplets trapped in phytoplankton aggregates were also described (Lee et al. 1985).
These earlier observations were not pursued, likely because such phytoplankton-oil
associations were thought to be relatively rare and quantitatively unimportant, in the
nearshore environments where oil exploration and production typically took place.
The potential of oil incorporation into marine snow became important, once drilling
in deep waters started, as sediment particles are too rare in these environments to
form OPAs. However, natural marine snow formation may be significant in such
environments and as was observed during the DwH oil spill. Marine oil snow (MOS)
differs from OMAs, OSAs, or oil-SPM, in that marine snow naturally forms in the
absence of oil, is per definition large (>0.5 mm), contains high amounts of organic
particles, and is fractal. The inclusion of oil compounds in marine snow results in
the formation of MOS.
12.3 Marine “Oil” Snow
Arguably, one of the most important discoveries about the fate of the DwH oil
spilled in the Gulf of Mexico in 2010 is the role of the interactions of marine snow
and oil and the consequences for the short- and long-term fate of oil chemicals and
dispersants and their deposition. MOS associated with the DwH spill consisted
largely of organic particles, including bacteria, phytoplankton, fecal material, feeding structures and detritus (Passow and Ziervogel 2016; Daly et al. 2016), and oilrelated compounds from the Macondo crude oil (OSAT 2010), all embedded in a
mucus-rich matrix formed from EPS/TEP (Fig. 12.2). Depending on the specific oil
compound, hydrocarbons may be incorporated into marine snow via sorption to
particles and as droplets caught in the marine snow matrix (Wirth et al. 2018).
However, incorporation of oil compounds into marine snow also depends on weathering processes – including evaporation, photooxidation, and biodegradation
(Brakstad and Faksness 2000) – as well as on dispersion and dissolution into the
water. Incorporation of oil into marine snow is a function of both available oil
A. Quigg et al.
Toxicity studies and numerical models were used to demonstrate habitat recovery
due to dispersion and biodegradation of the residual oil in these oil translocationbased studies (Lee et al. 2003b; Niu and Lee 2013).
The Deepwater Horizon (DwH) accident was the first oil spill in deep waters
where natural sediment and/or mineral particle concentrations are too low to cause
the formation of ubiquitous amounts of OPAs. Thus sedimentation of oil to depth
was not expected. However, significant amounts of oil were observed to accumulate
at the seafloor (e.g., Valentine et al. 2014; Chanton et al. 2015; Schwing et al. 2015;
Passow and Hetland 2016), resulting in the realization that marine snow can lead to
the vertical transport of large amounts of oil.
Significant sedimentation of hydrocarbons in association with phytoplankton
had already been observed about 30 years earlier in mesocosm studies (Lee and
Anderson 1977; Lee et al. 1978, 1985), but sorption and active uptake of oil compounds were considered the main causes (Lee et al. 1978), although whole oil droplets trapped in phytoplankton aggregates were also described (Lee et al. 1985).
These earlier observations were not pursued, likely because such phytoplankton-oil
associations were thought to be relatively rare and quantitatively unimportant, in the
nearshore environments where oil exploration and production typically took place.
The potential of oil incorporation into marine snow became important, once drilling
in deep waters started, as sediment particles are too rare in these environments to
form OPAs. However, natural marine snow formation may be significant in such
environments and as was observed during the DwH oil spill. Marine oil snow (MOS)
differs from OMAs, OSAs, or oil-SPM, in that marine snow naturally forms in the
absence of oil, is per definition large (>0.5 mm), contains high amounts of organic
particles, and is fractal. The inclusion of oil compounds in marine snow results in
the formation of MOS.
12.3 Marine “Oil” Snow
Arguably, one of the most important discoveries about the fate of the DwH oil
spilled in the Gulf of Mexico in 2010 is the role of the interactions of marine snow
and oil and the consequences for the short- and long-term fate of oil chemicals and
dispersants and their deposition. MOS associated with the DwH spill consisted
largely of organic particles, including bacteria, phytoplankton, fecal material, feeding structures and detritus (Passow and Ziervogel 2016; Daly et al. 2016), and oilrelated compounds from the Macondo crude oil (OSAT 2010), all embedded in a
mucus-rich matrix formed from EPS/TEP (Fig. 12.2). Depending on the specific oil
compound, hydrocarbons may be incorporated into marine snow via sorption to
particles and as droplets caught in the marine snow matrix (Wirth et al. 2018).
However, incorporation of oil compounds into marine snow also depends on weathering processes – including evaporation, photooxidation, and biodegradation
(Brakstad and Faksness 2000) – as well as on dispersion and dissolution into the
water. Incorporation of oil into marine snow is a function of both available oil
A. Quigg et al.