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.

As petroleum development and other activities move further north, the potential for oil spills in ice-covered waters is of great concern. As a tool for contingency planning and forecasting during response, oil spill models play a key role. With the development of new, high-resolution coupled ice-ocean models, better predictions of sea ice are becoming available. We have updated the OSCAR oil spill model to use sea-ice velocity and coverage fields from coupled ice-ocean models to improve simulation of oil fate and transport in ice-covered waters. We describe the implementation of oil transport in the presence of ice, and demonstrate the improvement by considering three case studies. We find clear improvement when taking ice velocity from a coupled ice-ocean model into account, compared to a heuristic model that uses surface current and wind velocity. The difference is found to be especially important in a response situation near the marginal ice zone.

In oil spill models, vertical mixing due to turbulence is commonly modelled by random walk. If the eddy diffusivity varies with depth, failing to take the derivative of the diffusivity into account in the random walk scheme will lead to incorrect results. Depending on the diffusivity profile, the result may be either over- or underprediction of the amount of surfaced oil. The importance of using consistent random walk schemes has been known for decades in, e.g., the plankton modelling community. However, it appears not to be common knowledge in the oil spill community, with inconsistent random walk schemes appearing even in recent publications. We demonstrate and quantify the error due to inconsistent random walk, using a simplified oil spill model, and two different diffusivity profiles. In the two cases considered, a commonly used inconsistent scheme predicts respectively 54% and 202% the amount of surface oil, compared to a consistent scheme.

We investigated the effects of a warmer climate, and seasonal trends, on the fate of oil spilled in the Arctic. Three well blowout scenarios, two shipping accidents and a pipeline rupture were considered. We used ensembles of numerical simulations, using the OSCAR oil spill model, with environmental data for the periods 2009–2012 and 2050–2053 (representing a warmer future) as inputs to the model. Future atmospheric forcing was based on the IPCC’s A1B scenario, with the ocean data generated by the hydrodynamic model SINMOD. We found differences in “typical” outcome of a spill in a warmer future compared to the present, mainly due to a longer season of open water. We have demonstrated that ice cover is extremely important for predicting the fate of an Arctic oil spill, and find that oil spills in a warming climate will in some cases result in greater areal coverage and shoreline exposure.

We calculate all the elements of the Mueller matrix for light scattering from a two-dimensional randomly rough lossy metal surface. The calculations are carried out for arbitrary angles of incidence by the use of nonperturbative numerical solutions of the reduced Rayleigh equations. We foresee that the ability to model polarization effects in light scattering from surfaces will enable better interpretation of experimental data and allow for the design of surfaces which possess useful polarization effects.