1. UKCCSC Benthic Mesocosm Experiments Steve Widdicombe with Amanda Beesley, Mary Brinsley, Sarah Dashfield, Chris Gallienne Carolyn Harris, Mike Kendall, Malcolm Liddicoat, David Lowe, Louise McNeill, Hazel Needham, Phil Nightingale, Christine Pascoe, Ken Perrett, Andy Rees, Fred Staff, Tony Staff, Malcolm Woodward.

2. Large pH changes can be seen in the sediment environment. The nature of pH depth profiles depend on the sediment type. Sediment type is important in determining the strength and direction of nutrient flux as is the faunal community structure. The Sediment Environment

3. Nereis v Brissopsis High tolerance to seawater acidification Increases uptake of nitrate Increased release of silicate No impact on phosphate flux Impact on nitrite and ammonium flux Highly vulnerable to seawater acidification Decreases uptake of nitrate Increased release of silicate Increased release of phosphate No impact on nitrite and ammonium flux

4. S. Widdicombe & H.R. Needham. In press. Impact of CO2 induced seawater acidification on the burrowing activity of Nereis virens (Sars 1835) and sediment nutrient. Marine Ecology Progress Series J.I. Spicer A. Raffo, & S. Widdicombe In press. Influence of CO2-related seawater acidification on extracellular acid-base balance in the velvet swimming crab Necora puber. Marine Biology H. Miles, S. Widdicombe, J.I. Spicer, & J. Hall-Spencer, 2007. Effects of anthropogenic seawater acidification on acid-based balance in the sea urchin Psammechinus miliaris. Marine Pollution Bulletin 54:89-96.

5. UKCCSC Modelling Jerry Blackford Nancy Jones

6. Carbon Capture and Storage What are the potential impacts of a leak?

7. Parameterising a leak Parameterising the rate and duration of a leak event is speculative; apart from the stochastic nature of such an event there is little information available to guide us towards realistic scenarios. Klausman (2003) reports preliminary estimates of seepage from a terrestial EOR – sequestration project in Colorado, USA of < 3800 tonnes CO 2.a -1 over an area of 78 km 2 with subsequent C 14 measurements indicating rates of < 170 tonnes CO 2.a -1. These estimates equate to 0.14 – 3.0 mmols C.m -2.d -1 which are the unit relevant to the model system. This compares with a typical DIC concentration of 2100 mmols C.m -3. The typical capacity of the pipelines used to deliver CO 2 to well systems, 100-250 mmscfd (million metric standard cubic feet per day). This equates to ~0.27 x 10 12 mmols carbon.d -1

8. The second issue, principally relating to fast-rate leak events is the behaviour of the resulting high pressure gas jet; its rate of travel to the surface, subsequent direct gassing to the atmosphere and the portion of gas that dissolves in the water column. There is evidence from natural shallow (<20m) high pressure gas seeps that the majority of CO 2 can transfer to the water column. Hence we assume for simplicity all CO 2 from a leak is dissolved. For low pressure seepages we assume all gas is dissolved in the bottom layer, for high pressure leaks we assume an equal distribution of CO 2 input through out the water column.

9. Scenarios: 1. Diffuse seepage: We assume a constant low level seepage of CO 2, spread homogeneously across the area of one model box (49 km 2 ), representing a notion of porosity in geological formations. We employ two seepage rates, 0.5 mmol C.m -2.d -1 representing the Colorado data and a x100 treatment of 50.0 mmol C.m -2.d -1. 2. Long term well head failure: We assume an unmitigatable fault in the well casing resulting in a catastrophic outgassing of ~5 million tonnes CO 2 over one year, five times the input rate at Sleipner, or 5 years worth of sequestered CO 2. 3. Pipeline fracture: We assume a fracture in a pipeline that persists for one day. We use an injection of 150 000 tonnes CO 2, approx 10 times a typical pipeline capacity and 50x the mean Sleipner injection. i.e. worst case scenarios

10. Assume that the point source leaks disperses instantaneously into a model 7km x 7km box. Clearly this is a weakness although the tidally driven horizontal mixing processes in the region are strong and would be capable of achieving this mixing within a few days. All modes of release were simulated at two sites, North (57.75N, 1.00E), approximating to the Forties oil field water column depth of 138m strongly stratified during the summer South (53.5N, 1.0E), representative of the Viking group of oilfields. depth of 28m mixed throughout the year. The pipeline failures were simulated at four times during the seasonal cycle on julian days 11, 101, 191 and 281.

11. We report the pH anomaly caused by each leak event. Much research is currently ongoing into the precise nature of ecosystem response to high CO 2 but because of the complexity this is as yet unquantifiable In order to give some guidance the pH anomalies might have the following effects, it should be noted that this is subjective and qualitative. <0.1: Perturbation probally insignificant. 0.1-0.2: Minimal likely effect, perturbation less than natural variability. 0.2-0.3: Perturbation ~ natural variability, potentially some impacts. 0.3-0.4: Some species experiencing moderate to significant impacts. >0.4: More wide ranging and significant to severe effects predicted.

12. Diffuse seepage of 0.5 mmol C.m -2.d -1 (~ Colorado data) Results in no discernable impact Diffuse seepage 50.0 mmol C.m -2.d -1 (x100 Colorado data) North South

13. Continuous leak ~5 million tonnes CO2 over one year Not masked Masked (<0.02) South North

14. -0.02 Sea bed N.b. Anomalies less than 0.02 pH units masked Surface Note: different colour scale

15. Temporary pipeline blowout, 150 000 tonnes CO 2 x10 pipeline capacity, ~x50 Sleipner injection rate North South

16. Comparison with atmospherically driven acidification

17. Summary Blackford, J.C., Gilbert, F.J., 2007. pH variability and CO 2 induced acidification in the North Sea. Journal of Marine Systems 64. 229-241. Initial results suggest that leaks from CCS will not have a major ecological impact on the regional scale, but would probably have localised significant effects. The general international consensus is that we simply do not yet know enough about mechanisms and effects to be confident in model predictions of ecological effects, although contemporary and paleo- evidence indictate significant / catastrophic impacts.

18. 10 metres 1 kilometre Model of small scale leak dispersal Nested set of water columns with turbulent mixing parameterised

19. Model of small scale leak dispersal