Numerical Modeling of the Interactions of Oil, Marine Snow, and Riverine Sediments in the Ocean

Abstract

Natural or spilled oil in the ocean can interact with marine snow and sediment from riverine sources and form Marine Oil Snow (MOS) aggregates including aggregates consisting of phytoplankton, detritus, and feces. Such aggregates have a fractal structure and can transport oil from the surface layers to greater depths in the ocean, eventually settling on the seafloor. In recent studies of the Deepwater Horizon and IXTOC‐1 oil spills in the Gulf of Mexico, this process was identified as one of the main mechanisms for transporting oil vertically in the water column. We have adapted a stochastic, one‐dimensional numerical model that uses coagulation theory to simulate MOS formation and sinking in the ocean and predict the time evolution of physical properties and spatial distribution of MOS. Here we present the model development, calibration, and validation with measured MOS field data in the Gulf of Mexico during the Deepwater Horizon spill. We use a sensitivity analysis to identify critical parameters, and suggest future model improvements and areas where further experimental investigation is needed to improve our understanding of MOS formation and sedimentation. The model can be used during response and planning activities associated with oil spills in the marine environments.

Progress in Operational Modeling in Support of Oil Spill Response

“…Moreover, they suggest further studies on the shear and differential settling mechanism on the collision rate and state that no dominant collision mechanism is present. Dissanayake et al [165] adopted a stochastic marine snow aggregate formation prediction model (Jokulsdottir and Archer [166]) and applied it to explain the evolution of marine snow aggregate formation during the DwH spill in the Gulf of Mexico. This study identifies the aggregate parameters: The stickiness of particles in the aggregate, the fractal dimension of the aggregates, and the aggregate break-up mechanism play important roles in predicting the aggregate size distributions at different depth levels in the water column and the settling fluxes of oil at the sea bottom.…”

Formation of Oil-Particle-Aggregates: Numerical Model Formulation and Calibration

“…Zhao et al (2016) developed an estimate for coagulation efficiency applied on the conceptual basis of sediment particles coating an oil droplet. Dissanayake et al (2018) cited values of alpha that ranged from 0.08 to 0.8, depending on the makeup of the particle (i.e., organic material, mineral content, oil content). However, these were not directly applicable to the solid OPAs conceptualized for this study, nor could they be directly implemented within the full coupled model.…”

“…Simulation of MOS has obtained substantial interest since the Deepwater Horizon oil spill. For example, Dissanayake et al (2018) developed a one-dimensional model to simulate MOS formation and settling in the ocean. This provided valuable insight into the vertical processes that govern MOSSFA formation and transport, but to date these processes have not been included in a three-dimensional model capable of estimating dispersal.…”

“…Flocculation and aggregation models often assume a single average fractal dimension throughout all size ranges. For instance, Dissanayake et al (2018) chose a fractal dimension of 2.2 to represent the MOS aggregates in their one-dimensional model. FLOCMOD also assumes a constant fractal dimension (Verney et al, 2011;Sherwood et al, 2018).…”

A practical adsorption model for the formation of submerged oils under the effect of suspended sediments

“…The need to accurately model the fate and transport of spilled oils by suspended sediments is apparent when evaluating the risks of a potential spill or planning the response to an actual spill. 13,14 However, studies simulate oil sediment interactions and transport are limited, as are the parameters required to initiate transport models capable of prediction. 15 The over-arching objective of this study was to simulate oil sediment interactions and formation of submerged oils, to develop an adsorption model to calculate the formation of submerged oils under the effect of suspended sediments.…”