The effect of vertical mixing on the horizontal drift of oil spills

Johannes Röhrs,Knut-Frode Dagestad,Camilla Brekke,Cathleen E Jones,Tor Nordam,Jørgen Skancke,Helene Asbjørnsen

doi:10.5194/os-14-1581-2018

Abstract

Abstract. Vertical and horizontal transport mechanisms for marine oil spills are investigated using numerical model simulations. To realistically resolve the 3-D development of a spill on the ocean surface and in the water column, recently published parameterizations for the vertical mixing of oil spills are implemented in the open-source trajectory framework OpenDrift (https://doi.org/10.5281/zenodo.1300358, last access: 7 April 2018). The parameterizations include the wave entrainment of oil, two alternative formulations for the droplet size spectra, and turbulent mixing. The performance of the integrated oil spill model is evaluated by comparing model simulations with airborne observations of an oil slick. The results show that an accurate description of a chain of physical processes, in particular vertical mixing and oil weathering, is needed to represent the horizontal spreading of the oil spill. Using ensembles of simulations of hypothetic oil spills, the general drift behavior of an oil spill during the first 10 days after initial spillage is evaluated in relation to how vertical processes control the horizontal transport. Transport of oil between the surface slick and the water column is identified as a crucial component affecting the horizontal transport of oil spills. The vertical processes are shown to control differences in the drift of various types of oil and in various weather conditions.

Highlights

Oil spill modeling aims to describe the transport and fate of oil spilled at sea, whether from marine traffic, petroleum production, or other sources
The model is based on the Lagrangian particle-tracking model OpenDrift (Dagestad et al, 2018), the Automated Data Inquiring for Oil Spills (ADIOS) oil database and weathering library from National Oceanic and Atmospheric Administration (NOAA), and a number of recent parameterizations that describe the mass exchange between the surface slick and submerged oil
Functionality from OpenDrift is inherited by OpenOil, including particle advection, time stepping, and reading and interpolation of environmental input data from ocean, wave, and atmospheric models

Summary

Introduction

Oil spill modeling aims to describe the transport and fate of oil spilled at sea, whether from marine traffic, petroleum production, or other sources. The horizontal transport of oil spilled at sea is largely determined by ocean currents, waves, and winds. Ocean currents and the wave-induced Stokes drift vary with depth, and the wind drag is commonly assumed to only affect the surface slick (Reed et al, 1994; Drivdal et al, 2014). Modeling the transport and fate of spilled oil requires an accurate description of both surface slicks and the vertical distribution of submerged oil

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Discussion

Conclusion