Quantitative assessment of two oil-in-ice surface drift algorithms

The ongoing reduction in extent and thickness of sea ice in the Arctic might result in an increase of oil spill risk due to the expansion of shipping activity and oil exploration shift towards higher latitudes. This work assessed the response of two oil-in-ice surface drift models implemented in an open-source Lagrangian framework. By considering two numerical modeling experiments, our main finding indicates that the drift models provide fairly similar outputs when forced by the same input. It was also found that using higher resolution ice-ocean model does not imply better results. We highlight the role of sea ice in the spread, direction and distance traveled by the oil. The skill metric seems to be sensitive to the drift location, and drift model re-initialization is required to avoid forecast deterioration and ensure the accurate tracking of oil slicks in real operations.publishedVersio

Current shear and turbulence during a near-inertial wave

Surface currents and turbulent mixing were observed during a near-inertial wave (NIW) using an accousting doppler current profiler (ADCP) and satellite-tracked drifters. Drifter trajectories sampled at three depth levels show characteristics of an Ekman solution superposed with the NIW. Velocity and dissipation estimates from the ADCP reveal strong shear with a distinct constant flux layer in between the roughness length and a critical depth at 4m. Below, a shear free slab layer performing an inertial oscillation is observed. Dissipation, as estimated from the vertical beam of the ADCP, peaks in the wave-enhanced friction layer when the current opposes the wind and wave direction. Below the constant flux layer, maximum turbulence is observed when the NIW is in a phase that is in opposite direction to the time-averaged current. During this phase, currents at various depths rapidly realign in the entire boundary layer.publishedVersio

Potential sources of marine plastic from survey beaches in the Arctic and Northeast Atlantic

Plastic litter is accumulating on pristine northern European beaches, including the European Arctic, and questions remain about the exact origins and sources. Here we investigate plausible fishery and consumer-related sources of beach littering, using a combination of information from expert stakeholder discussions, litter observations and a quantitative tool - a drift model - for forecasting and backtracking likely pathways of pollution. The numerical experiments were co-designed together with practice experts. The drift model itself was forced by operational ocean current, wave and weather forecasts. The model results were compared to a database of marine litter on beaches, collected every year according to the standardized monitoring program of the Oslo/Paris Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR). By comparing the heterogeneous beach observations to the model simulations, we are able to highlight probable sources. Two types of plastic are considered in the simulations: floating plastic litter and submerged, buoyant microplastics. We find that the model simulations are plausible in terms of the potential sources and the observed plastic litter. Our analysis results in identifiable sources of plastic waste found on each beach, providing a basis for stakeholder actions.publishedVersio

Long term simulations of potential oil spills around Cuba

Simulations over eight years of continuous surface oil spills around Cuba are carried out to identify the most likely stranding (beaching) locations. The open source Lagrangian oil drift model OpenOil is applied with high resolution hydrodynamic forcing. The actual fraction of the released oil mass reaching different regions is calculated, revealing small differences between a light and a heavy crude oil type. Similar stranding rates for the two oil types are found. Another important conclusion is that, due to the high temporal variability in stranding rates, short term simulations of a few weeks are not suitable to assess environmental risk. The highest stranding rates are simulated in winter in Northern Cuba. It is also found that oil could reach Northern Cuba, Yucatan or Florida in about 3–5 days after a spill.publishedVersio

SAR wind measurements over open ocean in the Svalbard area

The objective of this study has been to investigate the possibility to retrieve ocean surface wind from SAR images in the Svalbard area and the marginal ice zone. The CMOD4 wind algorithm has been implemented for use with ENVISAT ASAR Wideswath, Image Mode and Alternating Polarisation images. The algorithm runs automatically on ASAR images obtained from ESA rolling archive every day, using wind direction from NCEP fields. During the project a number of wind fields derived from SAR has been collected for different wind situations in the Svalbard area. The most important wind phenomena that have been observed in the SAR data are the gap winds (or jet streams) coming out of the valleys and straits. Also local wind structures outside the ice edge such as polar lows and wind fronts have also been observed. To validate the SAR- derived wind fields, we used data from an oceanographic buoy in the Barents Sea, localized southwest of Bjørnøya. This is one of two buoy that have been in operation since March 2007, providing data in real time available from a website. It was first planned to use meteorological data from several met-stations around Svalbard, but the wind measurements for these buoys are biased by local topography. The wind data from the open ocean buoy southwest of Bjørnøya, taken near simultaneously with the SAR data, were extracted and compared with the SAR wind retrievals. In the period March – September we collected about 70 co-located data points which we used to make a quantitative comparison between the two data sets. The result of this comparison is that there is reasonable good agreement between the wind speed from SAR and from in situ measurements. The SAR wind speed is slightly higher than the in situ wind speed. Since the CMOD algorithm produces wind speed at 10 m height above the sea surface and the buoy provides wind data at 2 m height, some discrepancy between the two methods is expected. The SAR wind maps are disseminated via a webpage which is temporarily password-protected. The web site will be open after we have completed a validation period in 2008. The possibilities to provide operational wind fields from SAR has been investigated. The wind fields are produced automatically every time there is a SAR image available over open ocean provided from ESA rolling archive. At present there is limited SAR coverage over the study area, with typically 2 – 4 images per week. This is useful for research and demonstration work, but for fully operational monitoring it is necessary to obtain SAR wind fields twice per day in the Svalbard area and the marginal ice zone. The SAR wind data are presently tested by met.no in the ArcChange and OOMM projects. Further studies of SAR wind is conducted in the ongoing ESA project “SAR ocean wind, waves and currents”.NERSC Technical Report no. 391. Funded by Norwegian Space Centre, Contract no. JOP.07.06.