Scottish Marine and Freshwater Science Volume 5 Number 3: The Science of Deepwater Oil Spills - Results from the 2013 Marine Scotland Science Workshop

Theme 1 - Oceanography of the Faroe Shetland Channel and Scottish Shelf Break

State Of The Art

Presentations:

1. Setting the scene (Bill Turrell, MSS).
2. Marine Scotland Science monitoring/research and collaborative projects (Bee Berx, MSS).
3. Internal mixing processes (Mark Inall, SAMS).
4. Eddies (Toby Sherwin, SAMS)

The introductory talks illustrated the complexity of the oceanographic processes in the FSC and off the Scottish shelf break. In addition to a complex residual circulation, with currents at different vertical levels in the water column and across the area transporting water in sometimes opposite directions, there is a strong internal tide, generating intense pulses at points such as the seabed, and localised and intense mixing events e.g. when internal waves break.

There is also considerable meso-scale variability in currents, with meanders and eddies, and considerable spatial variability in these phenomena. A long established monitoring effort takes place in the area, in addition to more focused process studies and observations spanning over several decades. However, even though a wide range of methods are being used (ship-based hydrographic observations, moored profiling current meters, satellite altimetry and other remote sensing methods) and new methods are appearing on the horizon (e.g. HF radar, autonomous underwater vehicles), observations remain relatively sparse in the context of the spatial and temporal scales of the processes controlling the oceanographic variability in the area.

Specific items identified by the workshop participants in the discussions to characterise the state of the art were:

• Wind Field Variability: We need an adequate description of variability in wind field patterns, something that was not addressed in the review presentations. A related topic refers to characterising the effect of wind rotation (vorticity) on the circulation in the area.
• Vertical Interactions: Deep currents, including those generated by phenomena such as internal tides, can interact with surface currents. We need to characterise such interactions - an aspect likely to require additional research.
• Spatial Resolution: The degree of spatial variability was identified in some of the review talks. Such variability needs to be taken into account to avoid the dangers of inadequate spatial resolution in models. A key question remains, what is the minimum spatial resolution needed to model the key dispersion processes in the FSC?
• Remote Sensing: Sea Surface Temperature ( SST) and altimetry are useful remote sensing products but additional remote sensing products should be considered to study the oceanography of the area, e.g. HF Radar. However, surface sensing from satellites or radar is valuable but how well does it represent conditions within the water column?
• Ocean-shelf Exchange: Ocean-shelf exchange was not explicitly addressed by the presentations. However, it is the subject of on-going research (e.g. the FASTNEt project http://www.bodc.ac.uk/projects/uk/fastnet/project_overview/) It needs to be considered as most socio-economic impacts of spilled oil will be on the continental shelf.
• Distant Waters: The review concentrated on the FSC, which is understandable, but released oil may move quickly into other areas (i.e. the Norwegian Sea and the Iceland Basin); can we be confident that we understand the oceanography (and can model it) in those areas? Is the focus of the current exercise too local and should it be extended to other areas that can be affected, e.g. the Minch, the Fair Isle Gap? Coastal processes were not mentioned, and will become of importance as oil spreads.
• Additional Data Sources: There are additional data sources beyond the ones presented, such as the UK Met Office, the offshore oil and gas industry, the MoD, and international datasets. These should be captured in a more comprehensive review.
• Academic Modellers/End User Disconnect?: How well can our understanding of the oceanographic complexity reviewed here be used in operational modelling? Is there a disconnect between academia and end users?
• Internal Processes: Internal mixing is very important, as are vertical velocities. We also need to study the effect of overflows over ridges due to internal tides.
• Holistic Approach: In addition to individual processes, we also need to study and understand the interactions between these processes, i.e. take a more holistic approach.
• Data Assimilation: We need to discuss the options for real time monitoring and assimilating these data into models.

Knowledge Gaps

• Winter data/seasonality: There is a need for continuous winter data from throughout the water column (e.g. from gliders and other autonomous vehicles), as most of the data gathered is outside the winter period, for understandable reasons and with some brave exceptions.
• Horizontal Dispersion: We need a better quantification of horizontal dispersion.
• Intermittent Turbulence: Intermittent turbulence needs to be better understood and how this may affect an oil release close to its source.
• Shelf-Ocean Exchange: Observational evidence describing shelf-ocean exchange is still required to improve the models.
• Predictability: The degree of predictability of the processes under consideration needs to be quantified better to be able to incorporate them into models. Our understanding of the chaotic nature of the system is still relatively basic.
• Forecasting vs. Statistical Approach: A considerable body of observational evidence may be required for forecasting operationally, while a statistical modelling approach (identifying trends and patterns of variability at various temporal and spatial scales based on past observations) may help and be useful to planning operations.
• Real Time Observations: Present observations are far from real time at the moment, and this is needed if they are to be assimilated into models. It might be possible to use other locations for monitoring instruments such as offshore platforms.
• Interaction with Bathymetry: Bathymetric controlled processes and interactions with the sea bed are still not well understood.
• Process Spatial Scales: Specifically, the scale of the key processes under consideration at exploration areas needs to be described adequately.

Future Directions

• The Top Five Processes: Coming up with top five processes resulting in the dispersion of released oil may help focus minds and generate projects and attract funding.
• Spatial Integration: We need to examine our present knowledge in a way that integrates across spatial scales and oceanographic regimes.
• Shelf-ocean Exchanges: Shelf-ocean exchanges are important and need to be better studied.
• Fill the Winter Data Gap: It is important to address knowledge gaps with long duration observations, including in winter.
• A Tracer Experiment?: It would be useful to carry out an "artificial oil spill" (tracer?) to track and predict, to challenge the existing models and to lead to improvements. Such an experiment would also further develop our ability to monitor spilled deepwater oil in a real situation.
• Predictability: Understanding predictability of processes better would be useful. Is the system truly chaotic? At what space/time scales is the system predictable?
• Use of Ships of Opportunity: Ferryboxes are likely to provide useful datasets and should be explored further. In this context we should note the SERPENT project ( http://www.serpentproject.com/default.php). Can we take advantage of observation opportunities in collaboration with the offshore oil and gas industry?
• An Instrument Pool: It was suggested that there should be an EU (or UK) collection, or register, of scientific equipment which could be used in emergency response (e.g. drifters, gliders, ROVs, ADCPs).
• Possible Funding Sources: There is a large range of potential funders of research in this area, e.g. NERC, EU, MoD, DECC, SG. We should consider ways of harnessing all of these, and bringing in other interests into the picture, including industry.