23This paper presents the initial results of a scientific drilling project to recover core 24 and pressurized fluid samples from a natural CO 2 reservoir, near the town of Green River, 25Utah. The drilling targeted a stacked sequence of CO 2 -charged Jurassic sandstone reservoirs 26 and caprocks, situated adjacent to a CO 2 -degassing normal fault. This site has actively 27 leaked CO 2 from deep supercritical CO 2 reservoirs at depth >2km within the basin for over 28 Geyser constrain mixing models which show that, within the Navajo Sandstone, the 49 reservoir fluids are undergoing complex mixing of: (i) CO 2 -saturated brine inflowing from 50 the fault, (ii) CO 2 -undersaturated meteoric groundwater flowing through the reservoir and 51 (iii) reacted CO 2 -charged brines flow through fracture zones in the overlying Carmel 52Formation caprock, into the formations above. Such multi-scale mixing processes may 53 significantly improve the efficiency with which groundwaters dissolve the migrating CO 2 .

An experimental forest ecosystem drought Drought is affecting many of the world’ s forested ecosystems, but it has proved challenging to develop an ecosystem-level mechanistic understanding of the ways that drought affects carbon and water fluxes through forest ecosystems. Werner et al . used an experimental approach by imposing an artificial drought on an entire enclosed ecosystem: the Biosphere 2 Tropical Rainforest in Arizona (see the Perspective by Eisenhauer and Weigelt). The authors show that ecosystem-scale plant responses to drought depend on distinct plant functional groups, differing in their water-use strategies and their position in the forest canopy. The balance of these plant functional groups drives changes in carbon and water fluxes, as well as the release of volatile organic compounds into the atmosphere. —AMS

Abstract. A scientific borehole, CO2W55, was drilled into an onshore anticline, near the town of Green River, Utah for the purposes of studying a series of natural CO2 reservoirs. The objective of this research project is to recover core and fluids from natural CO2 accumulations in order to study and understand the long-term consequences of exposure of supercritical CO2, CO2-gas and CO2-charged fluids on geological materials. This will improve our ability to predict the security of future geological CO2 storage sites and the behaviour of CO2 during migration through the overburden. The Green River anticline is thought to contain supercritical reservoirs of CO2 in Permian sandstone and Mississippian-Pennsylvanian carbonate and evaporite formations at depths > 800 m. Migration of CO2 and CO2-charged brine from these deep formations, through the damage zone of two major normal faults in the overburden, feeds a stacked series of shallow reservoirs in Jurassic sandstones from 500 m depth to near surface. The drill-hole was spudded into the footwall of the Little Grand Wash normal fault at the apex of the Green River anticline, near the site of Crystal Geyser, a CO2-driven cold water geyser. The hole was drilled using a CS4002 Truck Mounted Core Drill to a total depth of 322 m and DOSECC’s hybrid coring system was used to continuously recover core. CO2-charged fluids were first encountered at ~ 35 m depth, in the basal sandstones of the Entrada Sandstone, which is open to surface, the fluids being effectively sealed by thin siltstone layers within the sandstone unit. The well penetrated a ~ 17 m thick fault zone within the Carmel Formation, the footwall damage zone of which hosted CO2-charged fluids in open fractures. CO2-rich fluids were encountered throughout the thickness of the Navajo Sandstone. The originally red sandstone and siltstone units, where they are in contact with the CO2-charged fluids, have been bleached by dissolution of hematite grain coatings. Fluid samples were collected from the Navajo Sandstone at formation pressures using a positive displacement wireline sampler, and fluid CO2 content and pH were measured at surface using high pressure apparatus. The results from the fluid sampling show that the Navajo Sandstone is being fed by active inflow of CO2-saturated brines through the fault damage zone; that these brines mix with meteoric fluid flowing laterally into the fault zone; and that the downhole fluid sampling whilst drilling successfully captures this dynamic process.

Representative sandstone samples from Mesohellenic Trough (NW Greece) were selected to investigate the geochemical reactions that occur when they come in contact with CO 2 under representative in-situ conditions (T=70 o C, P=150bar, 6 months reaction in batch experiments). Those sandstones consisted of predominant calcite and quartz, with lesser amounts of feldspars, chlorite, ankerite, dolomite, kaolinite, montmorillonite and muscovite. After reaction with CO 2 , the brine became acidic and was enriched in cations as a result of mineral dissolution. Minor mineralogical changes were observed that involved: a) the dissolution of carbonate minerals and b) the incongruent dissolution of chlorite to form clays and silica. The results related to these, have been linked with geochemical modelling using the PHREEQC code. Simulation results for a 10 ka time period predicted that chlorite was expected to dissolve completely within 100 years, leading to boehmite growth and increasing the mass of dolomite. Feldspars were expected to react at a later stage in the reaction sequence. Sensitivity tests were run to access the effect of various adjustable parameters on the outcome results. The geochemical experiments and modelling lend support to the view that Pentalofos and Tsotyli sandstone formations of the Mesohellenic Trough are suitable for the long-term storage of CO 2 produced in the neighbouring lignite-fired power plants, at least in terms of mineralogy and geochemistry.

The UK may be required to expand its bioenergy production in order to make a significant contribution towards the delivery of its 'net zero' greenhouse gas emissions target by 2050. However, some trees grown for bioenergy are emitters of volatile organic compounds (VOCs), including isoprene and terpenes, precursors in the formation of tropospheric ozone, an atmospheric pollutant, which require assessment to understand any consequent impacts on air quality. In this initial scoping study, VOC emission rates were quantified under UK climate conditions for the first time from four species of eucalypts suitable for growing as short-rotation forest for bioenergy. An additional previously characterised eucalypt species was included for comparison. Measurements were undertaken using a dynamic chamber sampling system on 2-3 year-old trees grown under ambient conditions. Average emission rates for isoprene, normalised to 30 °C and 1000 μmol m −2 s −1 PAR, ranged between 1.3 μg C g dw −1 h −1 to 10 μg C g dw −1 h −1 . All the eucalypt species measured were categorised as 'medium' isoprene emitters (1-10 μg C g dw −1 h −1 ). Total normalised monoterpene emission rates were of similar order of magnitude to isoprene or approximately one order of magnitude lower. The composition of the monoterpene emissions differed between the species and major compounds included eucalyptol, α-pinene, limonene and β-cisocimene. The emission rates presented here contribute the first data for further studies to quantify the potential impact on UK atmospheric composition, if there were widespread planting of eucalypts in the UK for bioenergy purposes.