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Studies of the subsurface microbiology of the Äspö Hard Rock Laboratory, Sweden have revealed the presence of many different bacteria in the deep groundwaters which appear to maintain reducing conditions. Experiments were conducted to study the rock-water and microbial interactions. These used crushed Äspö diorite, Äspö groundwater and iron- and sulphate-reducing bacteria in flowing systems under anaerobic conditions. In column experiments, there was evidence of loss and mobilization of fine-grained crushed material (<5 μm) which had originally adhered to grain surfaces in the starting material. The mobilized fines were trapped between grains. The degree of mineralogical alteration was greater in the experiments when bacteria were present. In both column and continuously stirred reactor experiments, there is evidence for the formation of a secondary clay. These experiments have shown that microbial activity can influence rock-water interactions even in nutrient-poor conditions.

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The significance of the potential impacts of microbial activity on the transport properties of host rocks for geological repositories is an area of active research. Most recent work has focussed on granitic environments. This paper describes pilot studies investigating changes in transport properties that are because of microbial activity in sedimentary rock environments in northern Japan. For the first time, these short experiments (39 days maximum) have shown that the denitrifying bacteria, Pseudomonas denitrificans, can survive and thrive when injected into flowthrough column experiments containing fractured diatomaceous mudstone material and synthetic groundwater under pressurised conditions. Although there were few significant changes in the fluid chemistry, changes in the Microbiological impacts -mudstone 2 permeability of the biotic column were quantitatively monitored. These same methodologies could also be adapted to obtain information from cores originating from a variety of geological environments including oil reservoirs, aquifers and toxic waste disposal sites to provide an understanding of the impact of microbial activity on the transport of a range of solutes, such as groundwater contaminants and gases (e.g. injected carbon dioxide).

The sequestration of CO 2 in the deep geosphere is one potential method for reducing anthropogenic emissions to the atmosphere without necessarily incurring a significant change in our energy-producing technologies. Containment of CO 2 as a liquid and an associated hydrate phase, under cool conditions, offer an alternative underground storage approach compared to conventional supercritical CO 2 storage at higher temperatures. We briefly describe conventional approaches to underground storage, review possible approaches for using CO 2 hydrate in CO 2 storage generally, and comment on the important role CO 2 hydrate could play in underground storage. Cool underground storage appears to offer certain advantages in terms of physical, chemical and mineralogical processes, which may usefully enhance trapping of the stored CO 2 . This approach also appears to be potentially applicable to large areas of sub-seabed sediments offshore Western Europe. words, 73 references, 6 figuresKeywords: Carbon dioxide. CO 2 , underground storage, sequestration, hydrate Running title: CO 2 HYDRATE AND UNDERGROUND STORAGE CO 2 HYDRATE AND UNDERGROUND STORAGE It is now widely accepted the rising levels of carbon dioxide (CO 2 ) in the Earth's atmosphere are causing global climate change, and this is a subject of international concern (e.g. IPCC 1990IPCC , 2007. Furthermore, if something is not done to reduce emissions of greenhouse gases to the atmosphere, predictions suggest an unprecedented rate of future temperature increase, with unknown, but possibly rapid, consequences for the global climate. Measurements show that global temperatures rose by 0.3-0.6°C in the 20th century. If the trends in current emissions continue there are suggestions (Karl et al. 2000;RCEP 2000) that the global mean temperature is likely to be about 3°C higher than at present by the end of the 21 st century. The main difficulty in attempting to combat climate change is the world population's high dependence on fossil fuels as an energy source. Alternatives such as solar energy and other renewables are making a useful contribution, and some countries presently rely heavily on nuclear power, nonetheless, the culture and lifestyle of many countries appear to be strongly linked to fossil fuel usage for many years to come.Assuming that we continue to burn fossil fuels, yet wish to mitigate CO 2 emissions to the atmosphere, we are faced with a limited number of alternatives:1. To reduce our CO 2 emissions by using lower carbon fuels (e.g. gas instead of coal); 2. To utilise the produced CO 2 ; 3. To dispose of the CO 2 in another domain of the planet, such as the geosphere, the terrestrial biosphere or the oceans. In order to stabilise atmospheric CO 2 concentrations at current values, it may be necessary to reduce CO 2 emissions by 60% or more over the next 50 years (RCEP 2000). Although many countries are making strenuous efforts to reduce their CO 2 emissions, this is proving extremely difficult because all countries, and not just the developing ones, c...