175
et al. 2015; Larson et al. 2020). The overall seafloor spatial extent of the large
sedimentation event, as calculated by increased
210
Pb xs flux after 2010, ranged
from 12,805 to 35,425 km
2
. The benefit of using
210
Pb xs flux as a complimentary
tool to petroleum tracers for validation of modeling results is the constraint of the
overall spatial extent of increased flocculent mass flux from the water column,
beyond the oil fraction.
Specifically for the deep sea, both studies demonstrated a large deposition event
following the DWH spill of petroleum hydrocarbons (Romero et al. 2017) and sediments (Schwing et al. 2017) over ~34,000 km
2
, mostly around the wellhead. This
unexpected and prolonged deposition of oil and sediments to the seafloor has been
referred as MOSSFA (marine oil snow sedimentation and flocculent accumulation,
Daly et al. 2016) and was initially demonstrated in the DeSoto Canyon (Romero
et al. 2015; Brooks et al. 2015). These studies demonstrate the need for multidisciplinary approaches for better understating of complex processes such as submerged
oil spills.
11.3 Numerical Simulation Description
11.3.1 Modeling and Experimental Setup
Our study implements the existing oil application (Paris et al. 2012) of the
Connectivity Modeling System (CMS; Paris et al. 2013), to improve the expected
transport and fate of the live oil (or gas-saturated oil) spilled during the DWH accident and for providing a better tool for future deep-sea blowouts. The CMS oil
application performs Lagrangian particle tracking of oil droplets released at the trap
height above the wellhead. Particle transport calculations take into account 3D
ocean currents, temperature, salinity, multi-fractional droplet buoyancy, droplet
evolution due to biodegradation, and surface oil evaporation. The 4th order RungeKutta integration scheme forms the basis for particle advection in the model.
Computations of the vertical terminal velocity of a droplet are based on its density
and size, its Reynolds number, as well as on other the ambient conditions such as
water temperature, salinity, density, and kinematic viscosity (Zheng et al. 2003).
The model output is saved every 2 hours and includes oil droplets’ effective density, size, depth, and geographic location. Here the CMS model grid adapted horizontal grid spacing of 0.04 degrees and 20 layers in the vertical. The biodegradation
dynamics of the present study is based on high-pressure experiments and assumes a
different decay rate for the each of the oil droplet fractions. In the hydrocarbon
multi-fraction approach implemented in the oil module, all the pseudo-components
are now in the same oil droplet. This allows to account for dissolution processes
where the droplet shrinks with the partitioning of the oil compounds in the water
column (Jaggi et al. 2017). Post-processing algorithms further translate model output into oil concentrations (see Sect. 11.3.3). The DSD profiles for the untreated oil
and for the oil treated with Corexit 9500®, the chemical dispersant deployed at the
11 Far-Field Modeling of a Deep-Sea Blowout: Sensitivity Studies of Initial…
et al. 2015; Larson et al. 2020). The overall seafloor spatial extent of the large
sedimentation event, as calculated by increased
210
Pb xs flux after 2010, ranged
from 12,805 to 35,425 km
2
. The benefit of using
210
Pb xs flux as a complimentary
tool to petroleum tracers for validation of modeling results is the constraint of the
overall spatial extent of increased flocculent mass flux from the water column,
beyond the oil fraction.
Specifically for the deep sea, both studies demonstrated a large deposition event
following the DWH spill of petroleum hydrocarbons (Romero et al. 2017) and sediments (Schwing et al. 2017) over ~34,000 km
2
, mostly around the wellhead. This
unexpected and prolonged deposition of oil and sediments to the seafloor has been
referred as MOSSFA (marine oil snow sedimentation and flocculent accumulation,
Daly et al. 2016) and was initially demonstrated in the DeSoto Canyon (Romero
et al. 2015; Brooks et al. 2015). These studies demonstrate the need for multidisciplinary approaches for better understating of complex processes such as submerged
oil spills.
11.3 Numerical Simulation Description
11.3.1 Modeling and Experimental Setup
Our study implements the existing oil application (Paris et al. 2012) of the
Connectivity Modeling System (CMS; Paris et al. 2013), to improve the expected
transport and fate of the live oil (or gas-saturated oil) spilled during the DWH accident and for providing a better tool for future deep-sea blowouts. The CMS oil
application performs Lagrangian particle tracking of oil droplets released at the trap
height above the wellhead. Particle transport calculations take into account 3D
ocean currents, temperature, salinity, multi-fractional droplet buoyancy, droplet
evolution due to biodegradation, and surface oil evaporation. The 4th order RungeKutta integration scheme forms the basis for particle advection in the model.
Computations of the vertical terminal velocity of a droplet are based on its density
and size, its Reynolds number, as well as on other the ambient conditions such as
water temperature, salinity, density, and kinematic viscosity (Zheng et al. 2003).
The model output is saved every 2 hours and includes oil droplets’ effective density, size, depth, and geographic location. Here the CMS model grid adapted horizontal grid spacing of 0.04 degrees and 20 layers in the vertical. The biodegradation
dynamics of the present study is based on high-pressure experiments and assumes a
different decay rate for the each of the oil droplet fractions. In the hydrocarbon
multi-fraction approach implemented in the oil module, all the pseudo-components
are now in the same oil droplet. This allows to account for dissolution processes
where the droplet shrinks with the partitioning of the oil compounds in the water
column (Jaggi et al. 2017). Post-processing algorithms further translate model output into oil concentrations (see Sect. 11.3.3). The DSD profiles for the untreated oil
and for the oil treated with Corexit 9500®, the chemical dispersant deployed at the
11 Far-Field Modeling of a Deep-Sea Blowout: Sensitivity Studies of Initial…