Modelling of oil thickness in the presence of an ice edge.

Oil slick thickness is a key parameter for the behaviour of oil spilled at sea. It influences evaporation and entrainment, viable response options, and the risk to marine life at the surface. Determining this value is therefore of high relevance in oil spill modelling. In open water, oil can spread as thin films due to gravity alone, and may be further dispersed by horizontal diffusion and differential advection. In the presence of ice, however, a thin oil slick may become concentrated to higher thickness, if compressed against the ice edge. In the present study, we develop a simple model for the thickness of oil forced against a barrier by a current. We compare our theory to flume experiments, and obtain reasonable agreement. We describe an implementation in a Lagrangian oil spill model, and present some examples. We discuss the operational applicability, and suggest further research needs.

The use of PAH, metabolite and lipid profiling to assess exposure and effects of produced water discharges on pelagic copepods.

Several laboratory studies have demonstrated that exposure to oil components cause toxicity to copepods, however, this has never been shown in natural populations of copepods. In the present study, we sampled copepods in an area of the North Sea with high density of oil production platforms discharging produced water. Environmental modelling was used to predict produced water and copepod trajectories prior to copepod sampling in situ. To maximise output from a minimal number of field samples, a novel and combined methodology was developed to allow exploitation of the same extract for several purposes; contaminant body burden, lipidomics, and metabolomics analysis. PAH body burdens were low compared to laboratory experiments where correlations between PAH body burden and acute toxicity, reproduction and molecular endpoints had been established. Still, station-specific PAH profiles strongly indicated copepod exposure to PW. NMR metabolomics, focusing on water-soluble metabolites, suggested no correlation between metabolites and stations. Interestingly, lipidomics analyses suggested site-specific fingerprints and profiles displayed for acyl-glycerols and wax esters. Potential effects of produced water exposure on lipid metabolism in copepods cannot be ruled out and deserves more attention. Our study exemplifies the importance of incorporating novel and improved analytical methodologies in environmental monitoring.

Improving oil spill trajectory modelling in the Arctic.

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.

The sensitivity of the surface oil signature to subsurface dispersant injection and weather conditions.

Subsea blowouts have the potential to spread oil across large geographical areas, and subsea dispersant injection (SSDI) is a response option targeted at reducing the impact of a blowout, especially reducing persistent surface oil slicks. Modified Weber scaling was used to predict oil droplet sizes with the OSCAR oil spill model, and to evaluate the surface oil volume and area when using SSDI under different conditions. Generally, SSDI reduces the amount of oil on the surface, and creates wider and thinner surface oil slicks. It was found that the reduction of surface oil area and volume with SSDI was enhanced for higher wind speeds. Overall, given the effect of SSDI on oil volume and weathering, it may be suggested that tar ball formation, requiring thick and weathered oil, could possibly be reduced when SSDI is used.