Protecting the Arctic
Written evidence submitted by Professor Peter Wadhams
This constitutes an extension to the document "Oil Spills in Sea Ice – Past, Present and Future", which summarized the recommendations of an international conference held in September 2011. Here I add material about the impact of the thinning and retreat of the sea ice, and lay out more clearly what we know about how oil from an under-ice blowout will interact with the ice cover. My conclusion is that the mechanism by which oil interacts with a moving ice cover in winter guarantees that the oil will be spread around very large areas of the Arctic and then when it reappears on the ice surface this will be in such small patches that it cannot be removed successfully by burning or mechanical retrieval.
Our conclusions are:
• If a blowout occurs during the drilling season, the only way to avoid massive pollution of the Arctic is to install a pre-engineered capping system to bring the well under control before the drillship is driven off station by winter conditions.
• If this is unsuccessful and oil continues to flow through the winter and impinges on a moving ice cover, it will be absorbed by the ice, a new layer of ice will grow beneath it, and the resulting "oil sandwich" will be transported hundreds of miles with the oil within it undetectable and inaccessible.
• In spring (May onwards) the oil migrates upwards through the ice floes and reaches the snow-covered surface in a large number of tiny patches, each being the top of a brine drainage channel. Each patch is too small to burn and the oil pollution is too widespread for mechanical retrieval to be effective.
• The final fate of the oil, as spring moves to summer, is to be deposited into the ocean by the partial or complete melt of the floes. As the oil has been encapsulated all winter it retains its lighter fractions and is thus quite toxic to marine life and migratory birds, which congregate around the edge of the pack ice zone in summer.
• Once the oil has reached the ice underside, there is no type of human intervention which can be effective in removing more than a very small percentage of the spilled oil.
1.The oil blowout process
The conclusions above represent the consensus view achieved through a mixture of large-scale "real" field experiments, carried out in Canada and Norway from the 1970s to the early 2000s, and laboratory and theoretical modelling experiments. The start point is an assumed blowout in which, as in the Deepwater Horizon blowout, oil and gas come out together. A buoyant plume of gas bubbles builds up to a diameter of about 80-100 m and carries oil droplets upwards as coatings to the bubbles. This "sprays" the bottom of the ice with finely divided oil droplets over the width of the plume.
If we are dealing with fast ice (fig. i), i.e. ice which is not moving because of being in shallow water or pinned to the coastline, the gas pressure will break up the ice over the blowout site, and the oil may be largely confined to the resulting hole, especially as the dynamics of the plume will build up a lip of deeper ice around the hole which helps to contain the oil. In principle the oil, being confined in a small space, can be burned (a risky business if gas is present) or mechanically retrieved.
i. A blowout plume hits a fast ice surface and breaks a hole.
ii. Sequence of creation of an oil sandwich in moving ice. (Top) initial layer of oil gathered on ice bottom. (Middle) The oil is in a "sandwich" through new ice growth. (Bottom) The oil rises to the upper surface in spring through brine drainage channels.
2. Formation of the oil sandwich
Given the water depths at which drilling is planned, and the proposed use of drillships (with the ice pressure under summer conditions relieved by icebreakers circling around the drillship) it is more likely that a blowout, if not quickly capped, will emit gas and oil through a winter onto a moving ice surface. Ice off NE Greenland, in Baffin Bay and the Arctic Ocean will certainly be in motion; only the shallow Chukchi shelf, of the currently planned drilling areas, is likely to be covered with fast ice.
Moving ice typically moves at 5-10 km/day, giving a downstream drift through a winter of 1500-3000 km. The drift is wind driven and so is not regular in speed or direction, so the trajectory of a given ice floe is likely to include loops and other deviations from the long-term current direction.
The 100 m-wide "paintbrush" comprising the ice droplets in the rising plume are now not incident on a stationary surface but on a moving surface where the speed of the ice is such that the oil may not form a continuous layer under the ice. At modest oil flow rates (e.g. the 2500 barrels/day envisaged by early researchers) the oil is like a wide paintbrush with inadequate paint on it; it paints a discontinuous swath of oil onto the ice underside. At higher flow rates (e.g. the 30,000 barrels/day now stated as possible for the Chukchi Sea) the oil layer is continuous. The oil gathers in depressions and undulations under the ice, or up against the damming effect of pressure ridges, to form a pattern of slicks and pools of thickness up to tens of cm, but with a minimum thickness (set by surface tension) of about 1 cm (figure ii above).
As soon as the oil layer forms and is carried away from the active wellhead site by the current, new ice starts to grow underneath the oil layer and soon isolates it from the sea. It becomes an "oil sandwich". No trace of the oil can be found by vehicles (e.g. AUVs, autonomous underwater vehicles) operating under the ice, and no trace appears on the upper ice surface. To track the oil it would be necessary to release GPS buoys at frequent intervals over the blowout site so as to act as tracers for the oiled floes.
3. Springtime and the oil appears
What happens next has been well documented from an experiment in the Canadian Arctic (Balaena Bay) where oil was spilled under ice throughout a winter. The ice, especially if it is first-year ice, possesses a network of "brine drainage channels", narrow vertical filaments through which liquid brine contained within the ice gradually drains away during the winter (see diagram). In spring, the intense solar radiation causes these filaments to open up, grow thicker and melt their way towards the top of the ice. They provide an escape route for the oil, which is driven up the channels by its buoyancy and appears in small patches all over the floe, each patch being the top of a brine drainage channel, and each patch mixing with the surrounding snow. The ice cover is covered with spots. In the experiment described above this happened on May 5. The oil is far too diffuse to be burned or mechanically removed, and the process occurs at the same time on all of the floes that have been oiled through the winter – a trail 1500-3000 km long ending at the blowout site. This is a formidable challenge to clean-up, and no feasible method has been proposed that can deal with such widespread yet such diffuse oil pollution.
4. The end point
As spring turns into summer, the fate of the oil depends on where the floe is. If it is in the central Arctic, the snow on the ice surface will melt to create a network of melt pools on the surface which will now be oiled. This may offer an opportunity for some recovery. If the floe is near the ice edge it may melt away completely or break up, depositing the oil in the temporary open water of summer. Again a short window of opportunity for clean-up now occurs, but any skimmer needs to work in the vicinity of other ice floes and so the work would be small-scale and labour-intensive. Also the oil retains its toxicity because the winter encapsulation has prevented the lighter fractions from evaporating or dissolving. In the open water of the Canadian Arctic in summer millions of migratory birds are found (e.g eider ducks, guillemots), making use of the open water areas. These birds, and marine life such as whales, seals and plankton, would be very vulnerable.
5. The effects of climate change
We now have to consider the changes that have been produced by the thinning and retreat of sea ice. The sea ice cover of the Arctic Ocean, particularly in summer, has been in retreat since the 1950s at a rate of about 4% per decade which has recently increased to 10% per decade. More seriously, the thickness of the ice has diminished. Since 1971 I have been sailing to the Arctic in UK nuclear submarines, mapping the ice thickness using upward-looking sonar along the vessel’s track. Opening their submarines to scientific work has been a marvellous service to climate research by the Ministry of Defence, for which they deserve credit and the thanks of the scientific world. US submarines also operate in the Arctic, and in greater numbers, but do not consistently allow availability for scientific work. It was thanks to UK submarines that I was able to show for the first time that the ice in the Arctic is thinning (in a 1990 paper in Nature, showing a 15% thickness loss in 11 years), and recent work (the last voyage was in 2007 on "Tireless") from UK and US submarines now shows a loss of more than 43% in thickness between the 1970s and 2000s, averaged over the ocean as a whole. This is an enormous loss – nearly half of the ice thickness – and has changed the whole appearance of the ice cover. Pressure ridges, for instance, are now more rare and thinner, and are less of an obstacle for icebreakers, while most of the ice is now first-year rather than the formidable multi-year ice which used to prevail.
The thinning is caused by a mixture of reduced growth in winter, because of warmer temperatures and more heat in the underlying water column, and greater melt in summer. A change in the direction and speed of ice motion has also played a role, with the ice departing quicker from the Arctic Basin through Fram Strait rather than circulating many times inside the Arctic.
The summer (September) area of sea ice reached a record low in 2007 (fig. iii), almost matched in 2011, but what is most serious is that the thinning continues, so it is inevitable that very soon there will be a downward collapse of the summer area because the ice will just melt away. Already, in 2007, melt rates of 2 m were measured on the bottoms of thick floes in the Beaufort Sea, while the neighbouring first-year floes had only reached in 1.8 m during winter – so all first-year ice was disappearing. This effect will become more important and will spread throughout the Arctic Basin.
iii)Record ice retreat in September 2007 compared with 1970-2000 average (pink line).
There is currently disagreement about when the summer Arctic will become completely ice-free. It depends on what model is being employed. My own view is based on purely empirical grounds, that is, matching the observations of area from satellites with observations from submarines (combined with some modelling) of thickness to give us ice volume. If we think in volume terms instead of area terms, the downward trend is more than linear, in fact it is exponential, and if extrapolated it gives us an ice-free summer Arctic as early as 2015. Others have talked of later dates, like 2030-2040, but I do not see how the trend of summer ice volume can possible permit this. Those who agree include W Maslowsky, a leading ice modeller (Naval Postgraduate School, Monterey), and the PIOMAS project at University of Washington which generated the data shown below.
iv) (below). Minimum volume of Arctic sea ice in midsummer, based on areas observed from satellites and thickness trends inferred from submarine observations. Extrapolation leads to a zero volume in 2015.
6. Ice retreat and oil
The ice retreat is having some major impacts on the planet. Firstly, the increased open water reduces the planetary albedo (fraction of solar radiation reflected into space) and causes warming at high northern latitudes to be 2-4 times as fast as in the tropics, with enormous implications for climatic instability. Secondly, the summer retreat of the ice from the wide Arctic continental shelves (particularly the East Siberian Sea) allows the shallow surface layer to warm up, bringing temperatures of up to 5°C right down to the seabed. This is accelerating the melt of offshore permafrost, releasing methane trapped as methane hydrates and causing large plumes of methane to appear all over the summer Arctic shelves (observed for the last 2-3 summers by Semiletov and colleagues on joint University of Alaska – Far Eastern Research Institute cruises). Methane levels in the Arctic atmosphere have started to rise (measured by Dr Leonid Yurganov, Johns Hopkins University) after being stable for some years. As methane is a very powerful, if short lived, greenhouse gas (23 times as powerful per molecule as CO2 though only lasting about 7 years in the atmosphere instead of 100), this will give a strong upward kick to global warming. The implications of this will be discussed by my colleagues in the AMEG group (Arctic Methane Emergency Group) – we feel strongly that the situation is so serious that geoengineering methods must be considered to reduce the additional radiative forcing due to this new threat.
As far as oil is concerned, one might expect the oil industry to be pleased that the ice-free season will be longer and that winter ice growth is reduced. To an extent this is true, since the drilling season length will be increased. But it also means that a greater fraction of the year will feature broken-up rapidly-moving ice that is characteristic of the zone near the ice edge where wave action is effective, the so-called marginal ice zone (MIZ). An oil blowout in the MIZ raises a whole host of new paths for the spilled oil, notably the cracks and leads in between the floes. Through the random pumping action of the mobile ice floes, oil can be forced through leads and rapidly spread its influence over a large area. This does, of course, offer access to the oil as well and some scope for innovative clean-up techniques to be developed and tested.
The other difference is that the ice which develops the "oil sandwich" will have thinner "bread" on either side of the oil, and will give up its oil to the melting snow surface earlier in the spring.
APPENDIX. The Fermo statement.
For convenience I append again the conclusions reached by the panel of delegates at the recent oil-in-ice international workshop in Fermo, Italy. The statement is a list of what needs to be done before we can be said to be sure about the consequences of an oil blowout. Note that the very first desirable item listed is to prevent the oil from ever reaching the ice in the first place, by having a pre-engineering cap ready for action in case a blowout occurs late in the drilling season. This is better than relying on being able to drill a relief well in time. and far better than allowing oil to reach the ice through a winter, which would be a disaster for the Arctic environment.
The "Fermo statement" of research needs: (this has been delivered to the Arctic Council Task Force on oil protection)
1. How best to stop a blowout. Given the serious environmental impact of an oil blowout on the vulnerable Arctic, the highest priority must be given to methods which shorten the period during which release takes place. Until recently primary reliance has been placed on bringing in a second drilling rig and drilling a relief well even though it could take 60-90 days before successfully controlling and killing the well. Far more useful, in our view, would be a pre-engineered capping system with the ability to install a replacement blowout preventer. If prebuilt and available for rapid deployment such a system could much more rapidly bring the well under control. This is distinct from a containment system, also proposed by various oil companies, which collects oil from a blowout in a sort of hood, with the oil then needing to be removed from site and disposed of at intervals.
2. How to model oil spread. It is assumed that oil from a blowout rises in an oil-gas plume, impinges on the lower surface of an ice cover, is encapsulated by the growth of new ice underneath it, and drifts through the Arctic until released in spring by ascent through brine drainage channels to the ice surface. Every stage in this process needs to be modelled and studied more carefully, with special concern about the spring emergence process in the case of multiyear ice where the nature of the brine drainage channels is not well known. Models that have been developed for this process need to be intercompared, in the same way as the Arctic Sea Ice Model Intercomparison Project, to determine which models have validity and predictive power. The small-scale behaviour of oil being encapsulated in ice of different ages and types needs to be measured and modelled by laboratory experiments.
3. Tracking oil spills. We do not know enough about the detection of oil spills from space. This applies both to oil spills from marine accidents – ships which sink in ice – and to oiled ice from blowouts where the oil reaches the ice surface in spring and summer after being encapsulated in the ice and drifting with it during the winter. More work, including field trials, needs to be done with electro-optical sensors, including hyperspectral systems, ground penetrating and synthetic aperture radar (SAR). Technologically advanced satellite, aircraft, and unmanned airborne, seaborne and undersea systems should be exploited and integrated into an effective observing network.
4. Problems with in situ burning. Although in situ burning has been recommended and tested as a technique for disposal of Arctic oil, we do not fully understand the contribution to pollution by the smoke plumes or by the burn residue, especially its potential toxicity. The knowledge base needs to be assimilated into a rigorous net environmental benefit analysis (NEBA).
5. The role of dispersants needs to be studied in far greater detail, especially their potential chronic long-term effects. They have been employed in massive quantities in existing spills e.g. Gulf of Mexico, and are currently favoured as a treatment for an Arctic blowout, yet we need to know far more about their effectiveness and toxicity in the Arctic environment.
6. The physics of large-scale oil entrapment by features in the ice cover needs to be determined, so as to show whether simple geometric models of oil spread in rough ice are valid. In particular, the porosity of pressure ridges to oil needs to be determined experimentally.
7. The biological consequences of oil spills in Arctic waters need to be studied in greater detail. These can range from effects on large mammals (e.g. contamination of seal breathing holes) to small-scale effects (e.g. role of Arctic ocean bacteria in oil consumption, or the effects of sunken oil spill residues on the benthic community). Another key threat is to migratory birds who typically gather in marginal ice zone areas and leads in summer, which is exactly where and when previously entrapped oil is released into the environment. This is an area where the traditional knowledge of indigenous people can be of immense value in the detection of effects and changes, especially in habitats and species movements.
8. The rapidity of environmental change is affecting our oil-ice modelling in ways that we cannot fully encompass. Changes in water temperature, ice thickness and ice roughness affect both the mechanics of oil containment by ice and the physics and chemistry of oil interaction with the water column. We need to monitor key Arctic environmental change parameters systematically even though it can be a difficult or lengthy process to derive the rate of change of extreme parameters, such as the depth of the deepest pressure ridge in a given region or the areal extent of deformed ice.
9. Data sharing and management. It has often been the case that similar studies of oil-ice interaction have been carried out by industry and academia, with results not being fully shared. Future research on oil in ice should be carried out within the context of data interaction and sharing, such that full benefit can be gained by science from the efforts on both sides. A comprehensive data management system for oil-in-ice results would ensure maximum advantage from the limited opportunities that are available for controlled oil releases.
10. A rapid scientific response is needed when any opportunity arises to study oil-ice interaction in the field, e.g. a marine accident in ice. Any such event should be studied not just from the immediate viewpoint of clearing up the threatened pollution, but also with the larger aim of understanding the nature of the interactions that are taking place.
11. Delivery of the oil to the ice underside is a critical function of time of year and state of the sea or ice surface. Studies to date have focused on delivery to the bottom of an established first-year ice sheet, yet a blowout at the end of summer could begin with the oil interacting with a newly freezing water surface or with a variety of young ice types such as frazil, pancake or nilas. How early-winter oil is incorporated into a subsequently growing ice sheet needs to be studied.
12. The natural background should be studied in any spill situation. Natural oil seeps occur in many areas that are vulnerable to oil spills, e.g. along the Beaufort Sea coastline and in Baffin Bay, and have an impact which needs to be distinguished from the residual effects of a cleaned-up spill.
It is undeniable that prevention is always better than cure. Prevention of Arctic oil spills can be improved with better information and monitoring. Risks of a surface or subsurface oil spill from shipping or exploration drilling can be decreased if the operations are better designed for the geologic, marine traffic and environmental conditions that may be encountered in a changing Arctic. This includes designing for a wide range of changing ice conditions, storm events, and increased marine traffic. Better understanding of location specific risks requires high resolution temporal and spatial monitoring data and more research into low frequency extreme events.
The Oil Spills in Sea Ice workshop was not sponsored by either the oil industry or by NGOs. The concerns and recommendations expressed by its participants were based purely on our recognition of a clear scientific need.
The Chairman and organizer of the meeting was Dott. Maria Pia Casarini, Director of the Istituto Geografico Polare "Silvio Zavatti" (email [email protected]) and the organising committee comprised Prof. Peter Wadhams (University of Cambridge, [email protected]), David Dickins (DF Dickins Associates LLC, La Jolla, [email protected]), Dr Mark Myers (University of Alaska Fairbanks, [email protected]) and Dr Lawson Brigham (University of Alaska Fairbanks, [email protected]). The proceedings will be published by the Institute and refereed papers will appear in a special volume of the journal "Cold Regions Science and Technology"edited by Peter Wadhams.
13 February 2012