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overcome this problem by effectively ignoring it and considering all particles to
have the same stickiness and fractal dimension (Burd and Jackson 2009). Jackson
(1998) used a scaling argument to calculate the fractal dimension of a composite
particle, and a similar technique was used by Sterling et al. (2005). However, this
scaling technique might not be applicable when considering aggregates formed
from oil droplets and solid organic particles.
A different approach to modeling aggregation of heterogeneous particles uses a
stochastic Lagrangian approach (Jokulsdottir and Archer 2016; Dissanayake et al.
2018). This employs computational and stochastic techniques to represent individual particles and the collisions between them and is able to calculate the time evolution of the aggregate size distribution throughout the water column. The properties
of each individual aggregate can then be calculated from the properties of the constituent particles, all except the fractal dimension which is held constant. For example, Dissanayake et al. (2018) used different formulations for calculating aggregate
stickiness based on the volume fractions of oil, TEP, sediment particles, and organic
matter within each aggregate. The model was initialized with observed particle size
distributions in the surface waters and reproduced observed size distributions to
approximately 150 m at five locations near the DwH site reasonably well. The
model made predictions for the amount of oil settling to the sea floor that were
within the bounds of estimates made using observed tracer distributions. The model
results were sensitive to the value chosen for the fractal dimension and to the method
used to calculate the aggregate stickiness.
The theory of particle aggregation is well established and can provide valuable
insights into MOS formation and MOSSFA events. However, for it to become a
predictive tool will require a better understanding of key parameters such as aggregate fractal dimension and stickiness in the presence of oil and dispersants. If this
can be done, there is considerable potential for aggregation theory to become an
invaluable tool for first responders and oil spill research.
Acknowledgments This research was made possible by a grant from the Gulf of Mexico Research
Initiative to Quigg (ADDOMEx), Passow (ADDOMEx, ECOGIG, FOMOSA), Daly (C-IMAGE,
FOMOSA), Burd (FOMOSA), and Schwing/Hollander (C-IMAGE). Research support was also
provided by the University of South Florida Division of Sponsored Research and Florida Institute
of Oceanography to Daly and by the Multi-Partner Research Initiative, via the Department of
Fisheries and Oceans, Canada, to Passow.
References
Alldredge AL (2005) The contribution of discarded appendicularian houses to the flux of particulate organic carbon from oceanic surface waters. In: Gorsky G, Youngbluth MJ, Deibel D
(eds) Response of marine ecosystems to global change: ecological impact of appendicularians.
Éditions Scientifiques, Paris, 435 pp. ISBN:2-8470-302-9-8
Alldredge AL, Passow U, Logan BE (1993) The abundance and significance of a class of large,
transparent organic particles in the ocean. Deep-Sea Res I 40:1131–1140
12 Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) Events…
overcome this problem by effectively ignoring it and considering all particles to
have the same stickiness and fractal dimension (Burd and Jackson 2009). Jackson
(1998) used a scaling argument to calculate the fractal dimension of a composite
particle, and a similar technique was used by Sterling et al. (2005). However, this
scaling technique might not be applicable when considering aggregates formed
from oil droplets and solid organic particles.
A different approach to modeling aggregation of heterogeneous particles uses a
stochastic Lagrangian approach (Jokulsdottir and Archer 2016; Dissanayake et al.
2018). This employs computational and stochastic techniques to represent individual particles and the collisions between them and is able to calculate the time evolution of the aggregate size distribution throughout the water column. The properties
of each individual aggregate can then be calculated from the properties of the constituent particles, all except the fractal dimension which is held constant. For example, Dissanayake et al. (2018) used different formulations for calculating aggregate
stickiness based on the volume fractions of oil, TEP, sediment particles, and organic
matter within each aggregate. The model was initialized with observed particle size
distributions in the surface waters and reproduced observed size distributions to
approximately 150 m at five locations near the DwH site reasonably well. The
model made predictions for the amount of oil settling to the sea floor that were
within the bounds of estimates made using observed tracer distributions. The model
results were sensitive to the value chosen for the fractal dimension and to the method
used to calculate the aggregate stickiness.
The theory of particle aggregation is well established and can provide valuable
insights into MOS formation and MOSSFA events. However, for it to become a
predictive tool will require a better understanding of key parameters such as aggregate fractal dimension and stickiness in the presence of oil and dispersants. If this
can be done, there is considerable potential for aggregation theory to become an
invaluable tool for first responders and oil spill research.
Acknowledgments This research was made possible by a grant from the Gulf of Mexico Research
Initiative to Quigg (ADDOMEx), Passow (ADDOMEx, ECOGIG, FOMOSA), Daly (C-IMAGE,
FOMOSA), Burd (FOMOSA), and Schwing/Hollander (C-IMAGE). Research support was also
provided by the University of South Florida Division of Sponsored Research and Florida Institute
of Oceanography to Daly and by the Multi-Partner Research Initiative, via the Department of
Fisheries and Oceans, Canada, to Passow.
References
Alldredge AL (2005) The contribution of discarded appendicularian houses to the flux of particulate organic carbon from oceanic surface waters. In: Gorsky G, Youngbluth MJ, Deibel D
(eds) Response of marine ecosystems to global change: ecological impact of appendicularians.
Éditions Scientifiques, Paris, 435 pp. ISBN:2-8470-302-9-8
Alldredge AL, Passow U, Logan BE (1993) The abundance and significance of a class of large,
transparent organic particles in the ocean. Deep-Sea Res I 40:1131–1140
12 Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) Events…