A novel sub-seabed CO2 release experiment informing monitoring and impact assessment for geological carbon storage

Carbon capture and storage is a mitigation strategy that can be used to aid the reduction of anthropogenic CO2 emissions. This process aims to capture CO2from large point-source emitters and transport it to a long-term storage site. For much of Europe, these deep storage sites are anticipated to be sited below the sea bed on continental shelves. A key operational requirement is an understanding of best practice of monitoring for potential leakage and of the environmental impact that could result from a diffusive leak from a storage complex. Here we describe a controlled CO2release experiment beneath the seabed, which overcomes the limitations of laboratory simulations and natural analogues. The complex processes involved in setting up the experimental facility and ensuring its successful operation are discussed, including site selection, permissions, communications and facility construction. The experimental design and observational strategy are reviewed with respect to scientific outcomes along with lessons learnt in order to facilitate any similar future.

Modelling large-scale CO2 leakages in the North Sea

A three dimensional hydrodynamic model with a coupled carbonate speciation sub-model is used to simulate large additions of CO2into the North Sea, representing leakages at potential carbon sequestration sites. A range of leakage scenarios are conducted at two distinct release sites, allowing an analysis of the seasonal, inter-annual and spatial variability of impacts to the marine ecosystem. Seasonally stratified regions are shown to be more vulnerable to CO2release during the summer as the added CO2remains trapped beneath the thermocline, preventing outgasing to the atmosphere. On average, CO2 injected into the northern North Sea is shown to reside within the water column twice as long as an equivalent addition in the southern North Sea before reaching the atmosphere. Short-term leakages of 5000 tonnes CO2over a single day result in substantial acidification at the release sites (up to -1.92 pH units), with significant perturbations (greater than 0.1 pH units) generally confined to a 10 km radius. Long-term CO2leakages sustained for a year may result in extensive plumes of acidified seawater, carried by major advective pathways. Whilst such scenarios could be harmful to marine biota over confined spatial scales, continued unmitigated CO2emissions from fossil fuels are predicted to result in greater and more long-lived perturbations to the carbonate system over the next few decades.

Local perceptions of the QICS experimental offshore CO2 release: Results from social science research

This paper explores the social dimensions of an experimental release of carbon dioxide (CO2) carried out in Ardmucknish Bay, Argyll, United Kingdom. The experiment, which aimed to understand detectability and potential effects on the marine environment should there be any leakage from a CO2 storage site, provided a rare opportunity to study the social aspects of a carbon dioxide capture and storage-related event taking place in a lived-in environment. Qualitative research was carried out in the form of observation at public information events about the release, in-depth interviews with key project staff and local stakeholders/community members, and a review of online media coverage of the experiment. Focusing mainly on the observation and interview data, we discuss three key findings: the role of experience and analogues in learning about unfamiliar concepts like CO2 storage; the challenge of addressing questions of uncertainty in public engagement; and the issue of when to commence engagement and how to frame the discussion. We conclude that whilst there are clearly slippages between a small-scale experiment and full-scale CCS, the social research carried out for this project demonstrates that issues of public and stakeholder perception are as relevant for offshore CO2 storage as they are for onshore.

Late winter under ice pelagic microbial communities in the high Arctic Ocean and the impact of short-term exposure to elevated CO2 levels

Polar Oceans are natural CO2 sinks because of the enhanced solubility of CO2 in cold water. The Arctic Ocean is at additional risk of accelerated ocean acidification (OA) because of freshwater inputs from sea ice and rivers, which influence the carbonate system. Winter conditions in the Arctic are of interest because of both cold temperatures and limited CO2 venting to the atmosphere when sea ice is present. Earlier OA experiments on Arctic microbial communities conducted in the absence of ice cover, hinted at shifts in taxa dominance and diversity under lowered pH. The Catlin Arctic Survey provided an opportunity to conduct in situ, under-ice, OA experiments during late Arctic winter. Seawater was collected from under the sea ice off Ellef Ringnes Island, and communities were exposed to three CO2 levels for 6 days. Phylogenetic diversity was greater in the attached fraction compared to the free-living fraction in situ, in the controls and in the treatments. The dominant taxa in all cases were Gammaproteobacteria but acidification had little effect compared to the effects of containment. Phylogenetic net relatedness indices suggested that acidification may have decreased the diversity within some bacterial orders, but overall there was no clear trend. Within the experimental communities, alkalinity best explained the variance among samples and replicates, suggesting subtle changes in the carbonate system need to be considered in such experiments. We conclude that under ice communities have the capacity to respond either by selection or phenotypic plasticity to heightened CO2 levels over the short term.

Effects of elevated CO2 and temperature on an intertidal meiobenthic community

In the near future, the marine environment is likely to be subjected to simultaneous increases in temperature and decreased pH. The potential effects of these changes on intertidal, meiofaunal assemblages were investigated using a mesocosm experiment. Artificial Substrate Units containing meiofauna from the extreme low intertidal zone were exposed for 60 days to eight experimental treatments (four replicates for each treatment) comprising four pH levels: 8.0 (ambient control), 7.7 & 7.3 (predicted changes associated with ocean acidification), and 6.7 (CO2 point-source leakage from geological storage), crossed with two temperatures: 12 °C (ambient control) and 16 °C (predicted). Community structure, measured using major meiofauna taxa was significantly affected by pH and temperature. Copepods and copepodites showed the greatest decline in abundance in response to low pH and elevated temperature. Nematodes increased in abundance in response to low pH and temperature rise, possibly caused by decreased predation and competition for food owing to the declining macrofauna density. Nematode species composition changed significantly between the different treatments, and was affected by both seawater acidification and warming. Estimated nematode species diversity, species evenness, and the maturity index, were substantially lower at 16 °C, whereas trophic diversity was slightly higher at 16 °C except at pH 6.7. This study has demonstrated that the combination of elevated levels of CO2 and ocean warming may have substantial effects on structural and functional characteristics of meiofaunal and nematode communities, and that single stressor experiments are unlikely to encompass the complexity of abiotic and biotic interactions. At the same time, ecological interactions may lead to complex community responses to pH and temperature changes in the interstitial environment

Rapid response of the active microbial community to CO2 exposure from a controlled sub-seabed CO2 leak in Ardmucknish Bay (Oban, Scotland)

The response of the benthic microbial community to a controlled sub-seabed CO2 leak was assessed using quantitative PCR measurements of benthic bacterial, archaeal and cyanobacteria/chloroplast 16S rRNA genes. Samples were taken from four zones (epicentre; 25 m distant, 75 m distant and 450 m distant) during 6 time points (7 days before CO2 exposure, after 14 and 36 days of CO2 release, and 6, 20 and 90 days after the CO2 release had ended). Changes to the active community of microphytobenthos and bacteria were also assessed before, during and after CO2 release. Increases in the abundance of microbial 16S rRNA were detected after 14 days of CO2 release and at a distance of 25 m from the epicentre. CO2 related changes to the relative abundance of both major and minor bacterial taxa were detected: most notably an increase in the relative abundance of the Planctomycetacia after 14 days of CO2 release. Also evident was a decrease in the abundance of microbial 16S rRNA genes at the leak epicentre during the initial recovery phase: this coincided with the highest measurements of DIC within the sediment, but may be related to the release of potentially toxic metals at this time point.

Response of the ammonia oxidation activity of microorganisms in surface sediment to a controlled sub-seabed release of CO2

The impact of a sub-seabed CO2 leak from geological sequestration on the microbial process of ammonia oxidation was investigated in the field. Sediment samples were taken before, during and after a controlled sub-seabed CO2 leak at four zones differing in proximity to the CO2 source (epicentre, and 25m, 75m, and 450m distant). The impact of CO2 release on benthic microbial ATP levels was compared to ammonia oxidation rates and the abundance of bacterial and archaeal ammonia amoA genes and transcripts, and also to the abundance of nitrite oxidize (nirS) and anammox hydrazine oxidoreductase (hzo) genes and transcripts. The major factor influencing measurements was seasonal: only minor differences were detected at the zones impacted by CO2 (epicentre and 25m distant). This included a small increase to ammonia oxidation after 37daysof CO2 release which was linked to an increase in ammonia availability as a result of mineral dissolution. A CO2 leak on the scale used within this study (<1tonneday−1) would have very little impact to ammonia oxidation within coastal sediments. However, seawater containing 5% CO2 did reduce rates of ammonia oxidation. This was linked to the buffering capacity of the sediment, suggesting that the impact of a sub-seabed leak of stored CO2 on ammonia oxidation would be dependent on both the scale of the CO2 release and sediment type.

Impact of sub-seabed CO2 leakage on macrobenthic community structure and diversity

A sub-seabed release of carbon dioxide (CO2) was conducted to assess the potential impacts of leakage from sub-seabed geological CO2 Capture and Storage CCS) on benthic macrofauna. CO2 gas was released 12 m below the seabed for 37 days, causing significant disruption to sediment carbonate chemistry. Regular macrofauna samples were collected from within the area of active CO2 leakage (Zone 1) and in three additional reference areas, 25 m, 75 m and 450 m from the centre of the leakage (Zones 2, 3 and 4 respectively). Macrofaunal community structure changed significantly in all zones during the study period. However, only the changes in Zone 1 were driven by the CO2 leakage with the changes in reference zones appearing to reflect natural seasonal succession and stochastic weather events. The impacts in Zone 1 occurred rapidly (within a few days), increased in severity through the duration of the leak, and continued to worsen after the leak had stopped. Considerable macrofaunal recovery was seen 18 days after the CO2 gas injection had stopped. In summary, small short-term CCS leakage events are likely to cause highly localised impacts on macrofaunal communities and there is the potential for rapid recovery to occur, depending on the characteristics of the communities and habitats impacted.

Benthic megafauna and CO2 bubble dynamics observed by underwater photography during a controlled sub-seabed release of CO2

In 2012, a controlled sub-seabed release of carbon dioxide (CO2) was conducted in Ardmucknish Bay, a shallow (12 m) coastal bay on the west coast of Scotland. During the experiment, CO2 gas was released 12 m below the seabed for 37 days, causing significant disruption to sediment and water carbonate chemistry as the gas passed up through the sediment and into the overlying water. One of the aims of the study was to investigate how the impacts caused by leakage from geological CO2 Capture and Storage (CCS) could be detected and quantified in the context of natural heterogeneity and dynamics. To do this underwater photography was used to analyze (i) the benthic megafaunal response to the CO2 release and (ii) the dynamics of the CO2 bubble streams, emerging from the seabed into the overlying water column. The frequently observed megafauna species in the study area were Virgularia mirabilis (Cnidaria), Turritella communis (Mollusca), Asterias rubens (Echinodermata), Pagurus bernhardus (Crustacea), Liocarcinus depurator (Crustacea), and Gadus morhua (Osteichthyes). No discernable abnormal behavior was observed for these megafauna, in any of the zones investigated, during or after the CO2 release. Time-lapse photography revealed that the intensity and presence of the CO2 bubble plume was affected by the tides, with the most active bubbling seen at low tides and the larger hydrostatic pressure at high tide suppressing CO2 bubbling from the seabed.

Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios

The ocean moderates anthropogenic climate change at the cost of profound alterations of its physics, chemistry, ecology, and services. Here, we evaluate and compare the risks of impacts on marine and coastal ecosystems and the goods and services they provide for growing cumulative carbon emissions under two contrasting emissions scenarios. The current emissions trajectory would rapidly and significantly alter many ecosystems and the associated services on which humans heavily depend. A reduced emissions scenario consistent with the Copenhagen Accord’s goal of a global temperature increase of less than 2°C—is much more favorable to the ocean but still substantially alters important marine ecosystems and associated goods and services. The management options to address ocean impacts narrow as the ocean warms and acidifies. Consequently, any new climate regime that fails to minimize ocean impacts would be incomplete and inadequate.

Developments since 2005 in understanding potential environmental impacts of CO2 leakage from geological storage

This paper reviews research into the potential environmental impacts of leakage from geological storage of CO2 since the publication of the IPCC Special Report on Carbon Dioxide Capture and Storage in 2005. Possible impacts are considered on onshore (including drinking water aquifers) and offshore ecosystems. The review does not consider direct impacts on man or other land animals from elevated atmospheric CO2 levels. Improvements in our understanding of the potential impacts have come directly from CO2 storage research but have also benefitted from studies of ocean acidification and other impacts on aquifers and onshore near surface ecosystems. Research has included observations at natural CO2 sites, laboratory and field experiments and modelling. Studies to date suggest that the impacts from many lower level fault- or well-related leakage scenarios are likely to be limited spatially and temporarily and recovery may be rapid. The effects are often ameliorated by mixing and dispersion of the leakage and by buffering and other reactions; potentially harmful elements have rarely breached drinking water guidelines. Larger releases, with potentially higher impact, would be possible from open wells or major pipeline leaks but these are of lower probability and should be easier and quicker to detect and remediate.

An update to the Surface Ocean CO2 Atlas (SOCAT version 2)

The Surface Ocean CO2 Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO2 (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface water fCO2 values) and extended data coverage (from 1968–2007 to 1968–2011). The quality control criteria, while identical in both versions, have been applied more strictly in version 2 than in version 1. The SOCAT website (http://www.socat.info/) has links to quality control comments, metadata, individual data set files, and synthesis and gridded data products. Interactive online tools allow visitors to explore the richness of the data. Applications ofSOCAT include process studies, quantification of the ocean carbon sink and its spatial, seasonal, year-to-year and longer term variation, as well as initialisation or validation of ocean carbon models and coupled climate-carbon models.

The CO2 microalgae biorefinery: high value products and biofuels using halophilic microalgae in the “D-Factory”

Fuel-only algal systems are not economically feasible because yields are too low and costs too high for producing microalgal biomass compared to using agricultural residues e.g. straw. Biorefineries which integrate biomass conversion processes and equipment to produce fuels, power and chemicals from biomass, offer a solution. The CO2 microalgae biorefinery (D-Factory) is a 10 million Euro FP7-funded project which will cultivate the microalga Dunaliella in highly saline non-potable waters in photobioreactors and open raceways and apply biorefinery concepts and European innovations in biomass processing technologies to develop a basket of compounds from Dunaliella biomass, including the high value nutraceutical, β-carotene, and glycerol. Glycerol now finds markets both as a green chemical intermediate and as a biofuel in CHP applications as a result of novel combustion technology. Driving down costs by recovering the entire biomass of Dunaliella cells from saline cultivation water poses one of the many challenges for the D-Factory because Dunaliella cells are both motile, and do not possess an external cell wall, making them highly susceptible to cell rupture. Controlling expression of desired metabolic pathways to deliver the desired portfolio of compounds flexibly and sustainably to meet market demand is another. The first prototype D-Factory in Europe will be operational in 48 months, and will serve as a robust manifestation of the business case for global investment in algae biorefineries and in large-scale production of microalgae.

Dynamics of air–sea CO2 fluxes in the northwestern European shelf based on voluntary observing ship and satellite observations

From January 2011 to December 2013, we constructed a comprehensive pCO2 data set based on voluntary observing ship (VOS) measurements in the western English Channel (WEC). We subsequently estimated surface pCO2 and air–sea CO2 fluxes in northwestern European continental shelf waters using multiple linear regressions (MLRs) from remotely sensed sea surface temperature (SST), chlorophyll a concentration (Chl a), wind speed (WND), photosynthetically active radiation (PAR) and modeled mixed layer depth (MLD). We developed specific MLRs for the seasonally stratified northern WEC (nWEC) and the permanently well-mixed southern WEC (sWEC) and calculated surface pCO2 with uncertainties of 17 and 16 μatm, respectively. We extrapolated the relationships obtained for the WEC based on the 2011–2013 data set (1) temporally over a decade and (2) spatially in the adjacent Celtic and Irish seas (CS and IS), two regions which exhibit hydrographical and biogeochemical characteristics similar to those of WEC waters. We validated these extrapolations with pCO2 data from the SOCAT and LDEO databases and obtained good agreement between modeled and observed data. On an annual scale, seasonally stratified systems acted as a sink of CO2 from the atmosphere of −0.6 ± 0.3, −0.9 ± 0.3 and −0.5 ± 0.3 mol C m−2 yr−1 in the northern Celtic Sea, southern Celtic sea and nWEC, respectively, whereas permanently well-mixed systems acted as source of CO2 to the atmosphere of 0.2 ± 0.2 and 0.3 ± 0.2 mol C m−2 yr−1 in the sWEC and IS, respectively. Air–sea CO2 fluxes showed important inter-annual variability resulting in significant differences in the intensity and/or direction of annual fluxes. We scaled the mean annual fluxes over these provinces for the last decade and obtained the first annual average uptake of −1.11 ± 0.32 Tg C yr−1 for this part of the northwestern European continental shelf. Our study showed that combining VOS data with satellite observations can be a powerful tool to estimate and extrapolate air–sea CO2 fluxes in sparsely sampled area.