A Coupled Lagrangian-Earth System Model for Predicting Oil Photooxidation

Abstract

During the Deepwater Horizon (DWH) blowout, photooxidation of surface oil led to the formation of persistent photooxidized compounds, still found in shoreline sediments a decade later. Studies demonstrated that photooxidation modified both biodegradation rates of the surface oil and the effectiveness of aerial dispersant applications. Despite the significant consequences of this weathering pathway, the lack of measurements prevented photooxidation to be accounted for in the DWH oil budget calculations and in most predictive models. Here we develop a Lagrangian photooxidation module that estimates the dose of solar radiation individual oil droplets receive while moving in the ocean, quantifies the likelihood of photooxidative changes, and continues to track the transport of these persistent photooxidized compounds. We estimate and track the likelihood of photooxidation of Lagrangian oil droplets in the upper layers of the water column for the DWH case by coupling the net shortwave radiation from NOGAPS to the oil application of the Connectivity Modeling System (oil-CMS). The dose of solar radiation upon a droplet is computed with the intensity of the incoming irradiance at the ocean’s surface, the light attenuation coefficient, and the depth of the oil droplets. Considering a range of DWH empirical irradiance thresholds, we find that photooxidation can happen at short time scales of hours to days, in agreement with the new paradigm of oil photooxidation. Furthermore, the oxidized compounds are likely to form in a 110 km radius around the response site, suggesting that the oil reaching the coastline was already photooxidized. This new dynamic coupling provides a powerful tool to test oil weathering hypotheses, refine the oil budget during the DWH, and ultimately inform rapid response in future oil spills.

Source–sink recruitment of red snapper: Connectivity between the Gulf of Mexico and Atlantic Ocean

“…The CMS is an individual‐based model that estimates the movement of particles in a three‐dimensional velocity field, as forced by an oceanographic model. The framework has been used in a wide variety of modeling studies, including simulation of fish and invertebrate recruitment and oil spill modeling, and optional modules are provided that allow for complex behaviors and movements (Berenshtein et al, 2020; Drury et al, 2018; Faillettaz et al, 2018; Kough et al, 2016; Vaz et al, 2021). The specific CMS parameterization for red snapper has been outlined in detail within publicly available stock assessment literature (Karnauskas, Walter, & Paris, 2017), and we briefly summarize the details here.…”

Hot and Cold: Photochemical Weathering Mediates Oil Properties and Fate Differently Depending on Seawater Temperature

“…Current oil fate models include both the effect of evaporation on physical properties at a reference temperature and temperature adjustment calculations for evaporatively weathered oil . Models are also in the early stages of incorporating changes in oil chemical properties by sunlight (e.g., PAH degradation and oxygenation). − However, no spill model includes the effects of photochemical weathering on oil physical properties or partitioning behavior at any temperature. Our data provide quantitative information that may be used to update models, at least for light sweet oils like the one studied here.…”

Oil Transport Following theDeepwater HorizonBlowout

“…LCs can concentrate oil on the water surface in windrows (McWilliams & Sullivan 2000), which could reduce the oil-atmosphere interfacial area. The assumption of uniform horizontal oil distribution on the water surface or within a shallow depth (Vaz et al 2021, Ward et al 2018 could potentially lead to overestimates of the extent of photooxidation and/or evaporation, as both of these processes increase with the oil-atmosphere surface area. Farmer & Li (1994) used a hypothetical stream function formulation for a cross section of an LC (i.e., perpendicular to the wind direction) to obtain the water velocity distribution in an LC.…”