Sequestration Of Anthropogenic CO2 Research Articles

From biowaste to BioPave: Biological pathways for sequestration of anthropogenic CO2 and enhancing durability of roadway infrastructures

Biomass-derived bio-oils are emerging as sustainable, low-carbon alternatives for construction materials, particularly in innovative pavement applications, 'BioPave'. This study evaluates bio-oils from various sources, including algae and wastewater biomass, revealing variations in carbon, nitrogen, and sulfur contents, along with viscosity. We focused on their application in outdoor construction, assessing their resistance to thermal and solar radiation, and moisture. The study also examines their interaction with siliceous surfaces and their influence on asphalt adhesion in BioPave systems under moisture conditions. Laboratory experiments and computational modeling demonstrated molecular composition significantly influenced bio-oils' responses to thermal and UV exposure. Bio-oils rich in polar groups showed hardening upon thermal treatment, while those with higher concentrations of saturated aliphatics remained more stable. Furthermore, our findings highlight the significance of dosage control in maximizing beneficial effects of bio-oils in intermolecular interactions at bitumen-aggregate interface in BioPave applications. These findings offer insights into the potential of bio-oils in sustainable construction and the need for dosage control to optimize pavement performance.

Comparative studies on numerical sensitivity of different scenarios of enhanced oil recovery by water-alternating-gas (CO2) injection

Enhanced oil recovery by CO2 injection technology (CO2-EOR) plays a crucial role in enhancing oil production and the permanent sequestration of anthropogenic CO2 in depleted oil reservoirs. However, the availability of CO2 in oil field locations and its mobility in contrast with reservoir fluids are prime challenges in CO2-EOR. The cost of CO2 and its availability at the oil fields has prompted investigations on efficient injection of CO2 at the fields to achieve the best sweep efficiency possible. Injection strategies such as water-alternating-gas (WAG), simultaneous vertical and horizontal WAG, simultaneous water injection into the aquifer and vertical WAG, water and gas injection simultaneously but separately (SS-WAG), and water and gas injection simultaneously but not separately (SNS-WAG) play a significant role, as well as the purity of CO2. In this work, the significance of the above criteria was investigated individually and in combination. The coupled sequence of injection rate, soaking time, WAG ratio, and purity of injected CO2 for enhancement of oil production were delineated. A realistic reservoir simulation model conceptualizing the CO2-EOR system with five spot injection patterns was developed by the company CMG. The history-matched model that was developed was used to investigate the sensitivity of the coupled effects to the criteria listed above on oil recovery. Numerical investigations quantitatively emphasized that purity and soaking time of CO2 have an inverse effect in the oil production rate and that SNS-WAG resulted in a better oil production rate than SS-WAG.

Impacts of Different Operation Conditions and Geological Formation Characteristics on CO2 Sequestration in Citronelle Dome, Alabama

Major concerns of carbon dioxide (CO2) sequestration in subsurface formations are knowledge of the well injectivity and gas storage capacity of the formation, the CO2 pressure and saturation plume extensions during and after injection, and the risks associated with CO2 leakage and fault reactivation. Saline reservoirs are considered as one of the target formations for CO2 sequestration through structural, residual, dissolution, and mineral trapping mechanisms. The boundary condition of the saline reservoir dictates the pressure and saturation plume extension of the injected supercritical CO2 that could expand over large distances. This can lead to sources of risk, e.g., leakage and/or fault reactivation due to presence of wells, thief zones, and geological discontinuities. Therefore, there is a critical need to develop a model that describes how risk-related performance metrics (i.e., the CO2 saturation plume size, the pressure differential plume area, and the pressure differential at specific locations) vary as a function of the size of injection, time following injection, injection operations, and geologic environment. In this study, a systematic reservoir modeling studies of anthropogenic CO2 sequestration in Citronelle dome, Alabama, was performed where all relevant scenarios and conditions to address the questions of the saturation and pressure plume size in the area of review (AoR) and post-injection site care (PISC) are considered. The objective for this study was firstly to systematically simulate CO2 sequestration, i.e., saturation dynamics, and pressure behavior over a range of operational and geological conditions and to derive conclusions about the factors influencing saturation and pressure plume size, post-injection behavior, and the risk associated with them, by developing third-generation reduced order models (ROMs) for reservoir behavior. Finally, to assess the uncertainty associated with our studies, Latin Hypercube Sampling (LHS) together with an experimental design technique, i.e., Plackett–Burman design, was used. Application of Pareto charts and respond surfaces enabled us to determine the most important parameters impacting saturation and pressure plume sizes and to quantify the auto- and cross-correlation among different parameters in both history-matched and upscaled models.

CO2 storage potential in major oil and gas reservoirs in the northern South China Sea

As 41 % of China’s CO2 emission comes from coastal provinces and cities, permanent sequestration of anthropogenic CO2 in offshore sediments is a priority to achieve China’s national goal of net zero by 2060. In this paper we evaluate the potential of CO2 sequestration in the major oil and gas reservoirs in the northern South China Sea (NSCS) bordering the southern provinces of Guangdong, Guangxi and Hainan. The calculation of the CO2 storage potential is based on voidage replacement for individual oil and gas fields. Our study shows that the overall CO2 storage potential in oil and gas reservoirs in the four major geological basins in NSCS has low, mid and high value of 1015.8, 1082.7 and 1151.5 Mt, respectively. About 84 % of the storage potential resides in gas reservoirs and 16 % in oil reservoirs. Though this storage volume is modest, it is adequate for an industry scale CO2 storage demonstration project where one to several Mtpa CO2 can be injected. Furthermore, we have identified two relatively mature gas fields, Dongfang 1-1 and Yacheng 13-1 in the Yinggehai basin as potential candidates for such a demonstration project where industrial CO2 from Hainan Island can be sequestered permanently. A feasibility study on this is warranted.

Carbonate mineral identification and quantification in sediment matrices using diffuse reflectance infrared Fourier transform spectroscopy

Carbonate minerals are a major reservoir in the global carbon cycle and a key player in the sequestration and emission of atmospheric CO2. In addition to the minerals’ frequent use in agriculture and construction, carbonate formation has been targeted for anthropogenic CO2 sequestration. Due to carbonate’s importance in geological and anthropogenic realms, research on carbonate characterization and quantification is of interest. Here, we demonstrate a method to identify and quantify calcite (CaCO3) and dolomite (CaMg(CO3)2) in sediment matrices using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Needing only a few minutes per sample, DRIFTS is a rapid technique that does not require hazardous chemicals and does not destroy samples during analysis. We selected the 2515 ± 9 cm−1 absorbance bands for quantification as they exhibited little interference from sediment matrix minerals and large peak areas relative to other bands. The DRIFTS technique was compared to the traditional acidification headspace analysis method on artificial mixtures of sediment and carbonate as well as natural lake bed and river bank samples from the Upper Sangamon River Basin in Illinois, USA. DRIFTS offers an additional advantage over acidification in that it permits carbonate mineral identification simultaneously with its quantification. Though DRIFTS estimates were higher, a good correlation was found between DRIFTS and acidification estimates for both lake sediments (R2 = 0.99) and bank samples (R2 = 0.92), indicating DRIFTS is a reliable method for carbonate quantification in sediment matrices.

Linked Silurian carbon cycle perturbations, bursts of pinnacle reef growth, extreme sea-level oscillations, and evaporite deposition (Michigan Basin, USA)

Integration of sedimentologic, chemostratigraphic, biostratigraphic, and geochronologic data identifies the profound influence that sudden bursts of carbonate sedimentation, sea-level oscillation, and hypersalinity, associated with Ireviken and Mulde carbon cycle perturbations, had on the evolution of the Michigan Basin during the Silurian. Conodonts and carbon isotope (δ13Ccarb) stratigraphy of the Lockport and Engadine Dolomites constrain the rapid build-up and progradation of a thick biohermal wedge along the basin margins to the Sheinwoodian-age Ireviken Excursion, a recently identified period of global reef growth. This event significantly changed the hydrologic architecture of the basin, ultimately resulting in restricted seawater exchange that drove evaporite deposition. Zircon UPb ages of ~428 Ma from bentonites near the base of the evaporite-bearing Salina Group, together with δ13Ccarb profiles transecting the basin, constrain the onset of hypersalinity to initiation of the late Homerian Mulde Excursion. Importantly, the double δ13Ccarb peak of this event parallels a complex pattern of dramatic sea-level oscillations, on the order of 100 m, recorded within the A-0 to A-2 evaporites and associated pinnacle reefs. Ascending δ13Ccarb values were accompanied by sea-level fall, karstification, and the formation of evaporites in the basin center. Intra-excursion sea-level rebounds triggered exceptionally rapid upward pinnacle reef growth. Subsequent sea-level fall again exposed the ramp and pinnacle reefs resulting in basin-wide restriction and massive salt deposition that, ultimately, encased the reefs in salt. The return to baseline δ13Ccarb values was accompanied by flooding and carbonate sedimentation.Our integrated approach, with high-resolution δ13Ccarb stratigraphy from closely spaced (intra-basinal) sections as a central component, enables finely tuned chronostratigraphic correlation, recognition of unconformity-bound facies packages (i.e., systems tracts), and constrains variations in sea level and sedimentation rates. These findings have immediate applications to predictive static reservoir models for the evaluation of the reefs as repositories for anthropogenic CO2 sequestration, gas storage reservoirs, and hydrocarbon exploration. Ultimately, our findings demonstrate that a cascade of rapid environmental changes, including pulses of carbonate sedimentation, high-amplitude sea-level oscillations, and evaporite deposition, were associated with the Ireviken and Mulde perturbations of the Silurian carbon cycle.

Increased CO2 storage capacity using CO2-foam

Reduction of the CO2 mobility is beneficial during subsurface sequestration of anthropogenic CO2 in saline aquifers and hydrocarbon reservoirs by mitigating flow instabilities leading to early gas breakthrough and poor sweep efficiency. Injection of CO2 foam is a field-proven technology for gas mobility control. Foam generation and coalescence are compared between six commercially available surfactants with a range in CO2 solubility, during unsteady state injection of dense CO2-foam in a long sandstone outcrop core (1.15 m). Foam generation categories and foam decay were defined based on the observed changes in foam apparent viscosity during generation and coalescence. The degree of CO2 solubility influenced apparent viscosity development and peak foam strength for the tested surfactants. Variations in foam peak strength resulted in a range of water saturations at CO2 breakthrough (up to 24 percentage points difference observed experimentally), with implications for the CO2 storage capacity.

Deterministic tools to predict recovery performance of carbonated water injection

Carbonated water injection (CWI) is an efficient oil recovery method, which provides solution to the drawbacks of existing related recovery techniques such as water flooding and pure CO2 injection. The recovery factor achieved from CWI is considerably higher than that for related CO2- enhanced oil recovery (EOR) methods, due to effective transport phenomena involved in the displacement process. Additionally, the sequestration of anthropogenic CO2 makes CWI even more attractive for practical implications. Although CWI has been experimentally proven to be an efficient technique, simulation/mathematical models to capture detailed CWI physics have been unreliable because of the complex recovery mechanisms associated with CWI. A majority of models have been developed based on unrealistic assumptions. Thus, existing models become doubtful and the confidence to apply CWI in the larger scales such as pilot plants becomes low. In this research work, smart methods such as artificial neural network (ANN), least squares support vector machine (LSSVM), and gene expression programming (GEP) are suggested to avoid the impractical and inconclusive assumptions. The connectionist techniques (e.g., ANN, LSSVM, and GEP) relate the recovery factor (RF) to the key input parameters such as pressure, temperature, viscosity, permeability, and injection rate based on pattern recognition without detailed knowledge about the process as well as use of the governing equations. The performance of the deterministic models is evaluated through using statistical parameters such as mean squared error (MSE), maximum absolute percentage error (MAAPE), minimum absolute percentage error (MIAPE), and goodness of fit (R2). The results reveal that the ANN model has the lowest MSE (0.35), MIAPE (0.001), and MAAPE (2.47), and the highest R2 (0.99) in the testing phase. Based on the sensitivity analysis, pressure is recognized as the most important parameter, while temperature has the least rank in terms of significance. The findings of this research study can assist engineers and researchers to provide a reasonable estimation of RF achievable from CWI, which can be an asset in better management and planning of CWI processes toward optimal conditions in terms of technical, economic, and environmental prospects.

Accelerating Dissolution Trapping by Low Saline WAG Injection Scenario

Sequestration of anthropogenic CO2 into subsurface geologic formation is the most reliable methodology in stabilizing the ever increasing CO2 concentration in atmosphere. However the sequestered buoyant CO2 always tends to migrate back to the atmosphere through possible migration pathways. Ensuring storage safety by accelerating dissolution trapping is the only possible methodology, while dissolution is a strong function of pressure, temperature, salinity and local availability of brine. In the present paper, an attempt has been made to investigate the effect of salinity on accelerating dissolution of CO2 in resident brine. It has been observed that low saline brine injection enormously increases the dissolution trapping mechanism of injected CO2.

Recent Advances in Coal Seam Sequestration Research in India - Highlighting Multiphase CO2 Flow for Deep Seam Sequestration

India is a coal rich nation and has significant volumes of coalbed methane reserves. The recent developments in CBM production show a positive way of further research on understanding the reservoir behavior for carbon sequestration. India has the 3rd largest proven coal reserves and is the 4th largest producer of coal in the world. Moreover, the estimated CBM resources hold significant prospects for commercial recovery of the natural gas. The total CBM resource in India has been estimated to be around 4.6 TCM. Deeper reserves from which recovery of coal after CBM extraction seems less feasible, technologically as well as economically, may be the prime targets for sequestration of anthropogenic CO2. Coal seams that are found at depths which are below the limits of mining are considered suitable for disposal of anthropogenic CO2. Some estimates suggest that huge CO2 storage potential exists in the major coal fields in India and coal at depths more than 1200 m could store CO2 in the order of 345 Mt. Power sector in India is mostly coal based and produce huge quantities of CO2. There are several industries acting as point sources for CO2. The close proximity of deeper coals and location of large point sources of CO2 emission indicate the positives of sequestration in coal. Some basins have been marked with high sequestration potential of 1885 Mt in the Cambay basin while some like Singrauli could offer only 1-2 Mt of storage depending on various parameters.This study is a review of recent developments in the area of coal seam sequestration in India. A detailed analysis of the available literature was conducted along with few experiments on CO2-coal interactions. Few studies have been initiated in India to study the behaviour of Indian coal using CO2 and also to explore the possibility of enhanced recovery of coalbed methane. The trapping of CO2 in the coal seams is related to its capacity as well as the gas injectivity. Coal matrix shrinkage, swelling, gas diffusion and permeability have been significantly investigated over past few years. An important aspect which is yet to be fully understood is the role of phase transformation of CO2 on its hydro-mechanical behavior. Few experiments were conducted in our laboratory using different phases of CO2 in coal, obtained by varying pressure and temperature conditions. The changes in coal permeability due to supercritical CO2 flow were greatly attributed to the high volumetric deformation or the swelling of coal under supercritical CO2 as compared to liquid CO2. The injection pressures were observed to reduce the effective stress behavior, which in turn pushed the permeability evolution at each confinement to a positive trend. However, the permeability of CO2 reduced exponentially with increasing effective stresses.

Dissolution and secondary mineral precipitation in basalts due to reactions with carbonic acid

AbstractOne of the leading hydrothermal alteration processes in volcanic environments is when rock‐forming minerals with high concentrations of iron, magnesium, and calcium react with CO2 and water to form carbonate minerals. This is used to the advantage of geologic sequestration of anthropogenic CO2. Here we experimentally investigate how mineral carbonation processes alter the rock microstructure due to CO2‐water‐rock interactions. In order to characterize these changes, CO2‐water‐rock alteration in Auckland Volcanic Field young basalts (less than 0.3 Ma) is studied before and after a 140 day reaction period. We investigate how whole core basalts with similar geochemistry but different porosity, permeability, pore geometry, and volcanic glass content alter due to CO2‐water‐rock reactions. Ankerite and aluminosilicate minerals precipitate as secondary phases in the pore space. However, rock dissolution mechanisms are found to dominate this secondary mineral precipitation resulting in an increase in porosity and decrease in rigidity of all samples. The basalt with the highest initial porosity and volcanic glass volume shows the most secondary mineral precipitation. At the same time, this sample exhibits the greatest increase in porosity and permeability, and a decrease in rock rigidity post reaction. For the measured samples, we observe a correlation between volcanic glass volume and rock porosity increase due to rock‐fluid reactions. We believe this study can help understand the dynamic rock‐fluid interactions when monitoring field scale CO2 sequestration projects in basalts.

Performance assessment of CO2-enhanced oil recovery and storage in the Morrow reservoir

This paper presents a performance assessment methodology for CO2 enhanced oil recovery (EOR) in partially depleted reservoirs. A three dimensional heterogeneous reservoir model was developed for evaluating the CO2-EOR performance of in the Farnsworth Field Unit (FWU), Ochiltree County, Texas. The model aided in improved characterization of prominent rock properties within the Pennsylvanian-aged Morrow sandstone reservoir. Seismic attributes illuminated previously unknown faults and structural elements within the field. A laboratory fluid analysis was tuned to an equation of state and subsequently used to predict the thermodynamic minimum miscible pressure. Datasets including net-to-gross ratio, volume of shale, permeability, and burial history were used to model initial fault transmissibility based on Sperrevik model. An improved history match of primary and secondary recovery was performed to set the basis for a CO2 flood study. The performance of the current CO2 miscible flood patterns were subsequently calibrated to historical production and injection data. Several prediction models were constructed to study the effect of recycling, addition of wells and/or new patterns, water alternating gas cycles and optimum amount of CO2 purchase on incremental oil production and CO2 storage in the FWU. The history matching study successfully validated the presence of the previously-undetected faults within FWU that were seen in the seismic survey. The analysis of the various prediction scenarios showed that recycling a high percentage of produced gas, addition of new wells and a gradual reduction in CO2 purchase after several years of operation would be the best approach to ensure a high percentage of recoverable incremental oil and sequestration of anthropogenic CO2 within the Morrow reservoir.

Determining CO2 storage potential during miscible CO2 enhanced oil recovery: Noble gas and stable isotope tracers

Rising atmospheric carbon dioxide (CO2) concentrations are fueling anthropogenic climate change. Geologic sequestration of anthropogenic CO2 in depleted oil reservoirs is one option for reducing CO2 emissions to the atmosphere while enhancing oil recovery. In order to evaluate the feasibility of using enhanced oil recovery (EOR) sites in the United States for permanent CO2 storage, an active multi-stage miscible CO2 flooding project in the Permian Basin (North Ward Estes Field, near Wickett, Texas) was investigated. In addition, two major natural CO2 reservoirs in the southeastern Paradox Basin (McElmo Dome and Doe Canyon) were also investigated as they provide CO2 for EOR operations in the Permian Basin. Produced gas and water were collected from three different CO2 flooding phases (with different start dates) within the North Ward Estes Field to evaluate possible CO2 storage mechanisms and amounts of total CO2 retention. McElmo Dome and Doe Canyon were sampled for produced gas to determine the noble gas and stable isotope signature of the original injected EOR gas and to confirm the source of this naturally-occurring CO2. As expected, the natural CO2 produced from McElmo Dome and Doe Canyon is a mix of mantle and crustal sources. When comparing CO2 injection and production rates for the CO2 floods in the North Ward Estes Field, it appears that CO2 retention in the reservoir decreased over the course of the three injections, retaining 39%, 49% and 61% of the injected CO2 for the 2008, 2010, and 2013 projects, respectively, characteristic of maturing CO2 miscible flood projects. Noble gas isotopic composition of the injected and produced gas for the flood projects suggest no active fractionation, while δ13CCO2 values suggest no active CO2 dissolution into formation water, or mineralization. CO2 volumes capable of dissolving in residual formation fluids were also estimated along with the potential to store pure-phase supercritical CO2. Using a combination of dissolution trapping and residual trapping, both volumes of CO2 currently retained in the 2008 and 2013 projects could be justified, suggesting no major leakage is occurring. These subsurface reservoirs, jointly considered, have the capacity to store up to 9 years of CO2 emissions from an average US powerplant.

Role of deep convection on anthropogenic CO2 sequestration in the Gulf of Lions (northwestern Mediterranean Sea)

The most active deep convection area in the western Mediterranean Sea is located in the Gulf of Lions. Recent studies in this area provides some insights on the complexity of the physical dynamics of convective regions, but very little is known about their impacts on the biogeochemical properties. The CASCADE (CAscading, Surge, Convection, Advection and Downwelling Events) cruise, planed in winter 2011, give us the opportunity to compare vertical profiles of properties sampled either during stratified conditions or after/during a convection event. In the present study, we focus on the distributions of the carbonate system properties (mainly total alkalinity, AT; and total dissolved inorganic carbon, CT) because, in the context of the climate change, deep convection areas are suspected to significantly increase the sequestration of anthropogenic CO2 (CANT). Given its limited size, the impact of the Mediterranean Sea on the global carbon budget is probably minor but this marginal sea can be used as a laboratory to better understand carbon sequestration and its transfer to the basin interior by deep convection processes. Distributions of AT and CT, both measured from bottle samples, and that of CANT (estimated with the TrOCA approach) are first analyzed in the light of other key properties (salinity, temperature, and dissolved oxygen). An objective interpolation procedure is then applied to estimate CT and AT from CTD measured properties. With this procedure, the vertical resolution goes from a maximum of 32 samples per station to one property estimate every meter (more detailed distributions are obtained). Results provide arguments to conclude that CANT is rapidly transferred to the deepest layer due to deep convection events. During deep convection events, the increase of CANT in the water column is positively correlated to that of potential density and oxygen content. The challenge of quantifying the amount of sequestered carbon is however not resolved due to the complexity and the highly dynamical nature of the convective regions. Deep convection in the Gulf of Lions, in parallel with cascading along the continental slope, could thus potentially explain the very high levels of both CANT and acidification estimated in the deep layers of the western Mediterranean Sea.

The role of forest trees and their mycorrhizal fungi in carbonate rock weathering and its significance for global carbon cycling.

On million-year timescales, carbonate rock weathering exerts no net effect on atmospheric CO2 concentration. However, on timescales of decades-to-centuries, it can contribute to sequestration of anthropogenic CO2 and increase land-ocean alkalinity flux, counteracting ocean acidification. Historical evidence indicates this flux is sensitive to land use change, and recent experimental evidence suggests that trees and their associated soil microbial communities are major drivers of continental mineral weathering. Here, we review key physical and chemical mechanisms by which the symbiotic mycorrhizal fungi of forest tree roots potentially enhance carbonate rock weathering. Evidence from our ongoing field study at the UK's national pinetum confirms increased weathering of carbonate rocks by a wide range of gymnosperm and angiosperm tree species that form arbuscular (AM) or ectomycorrhizal (EM) fungal partnerships. We demonstrate that calcite-containing rock grains under EM tree species weather significantly faster than those under AM trees, an effect linked to greater soil acidification by EM trees. Weathering and corresponding alkalinity export are likely to increase with rising atmospheric CO2 and associated climate change. Our analyses suggest that strategic planting of fast-growing EM angiosperm taxa on calcite- and dolomite-rich terrain might accelerate the transient sink for atmospheric CO2 and slow rates of ocean acidification.

A review of mineral carbonation technologies to sequester CO2.

Carbon dioxide (CO2) capture and sequestration includes a portfolio of technologies that can potentially sequester billions of tonnes of CO2 per year. Mineral carbonation (MC) is emerging as a potential CCS technology solution to sequester CO2 from smaller/medium emitters, where geological sequestration is not a viable option. In MC processes, CO2 is chemically reacted with calcium- and/or magnesium-containing materials to form stable carbonates. This work investigates the current advancement in the proposed MC technologies and the role they can play in decreasing the overall cost of this CO2 sequestration route. In situ mineral carbonation is a very promising option in terms of resources available and enhanced security, but the technology is still in its infancy and transport and storage costs are still higher than geological storage in sedimentary basins ($17 instead of $8 per tCO2). Ex situ mineral carbonation has been demonstrated on pilot and demonstration scales. However, its application is currently limited by its high costs, which range from $50 to $300 per tCO2 sequestered. Energy use, the reaction rate and material handling are the key factors hindering the success of this technology. The value of the products seems central to render MC economically viable in the same way as conventional CCS seems profitable only when combined with EOR. Large scale projects such as the Skyonic process can help in reducing the knowledge gaps on MC fundamentals and provide accurate costing and data on processes integration and comparison. The literature to date indicates that in the coming decades MC can play an important role in decarbonising the power and industrial sector.

Changes in elastic wave velocity and rock microstructure due to basalt‐CO2‐water reactions

The chemical interaction between carbon dioxide, water, and basalt is a common process in the earth, which results in the dissolution of primary minerals that later precipitate as alteration minerals. This occurs naturally in volcanic settings, but more recently basalts have been suggested as reservoirs for sequestration of anthropogenic CO2. In both the natural and man‐made cases, rock‐fluid reactions lead to the precipitation of carbonates. Here, we quantify changes in ultrasonic wave speeds, associated with changes in the frame of whole‐rock basalts, as CO2 and basalt react. After 30weeks of reactions and carbonate precipitation, the ultrasonic wave speed in dry basalt samples increases between 4% and 20% and permeability is reduced by up to an order of magnitude. However, porosity decreases only by 2% to 3%. The correlation between significant changes in wave speed and permeability indicates that a precipitate is developing in fractures and compliant pores. Thin sections, XRF‐loss on ignition, and water chemistry confirm this observation. This means time‐lapse seismic monitoring of a CO2‐water‐basalt system cannot assume invariance of the rock frame, as typically done in fluid substitution models. We conclude that secondary mineral precipitation causes a measurable change in the velocities of elastic waves in basalt‐water‐CO2 systems, suggesting that seismic waves could be used to remotely monitor future CO2 injection sites. Although monitoring these reactions in the field with seismic waves might be complicated due to the heterogeneous nature of basalt, quantifying the elastic velocity changes associated with rock alteration in a controlled laboratory experiment forms an important step toward field‐scale seismic monitoring.

Key microbial drivers in Antarctic aquatic environments

Antarctica is arguably the world's most important continent for influencing the Earth's climate and ocean ecosystem function. The unique physico-chemical properties of the Southern Ocean enable high levels of microbial primary production to occur. This not only forms the base of a significant fraction of the global oceanic food web, but leads to the sequestration of anthropogenic CO2 and its transport to marine sediments, thereby removing it from the atmosphere; the Southern Ocean accounts for ~ 30% of global ocean uptake of CO2 despite representing ~ 10% of the total surface area of the global ocean. The Antarctic continent itself harbors some liquid water, including a remarkably diverse range of surface and subglacial lakes. Being one of the remaining natural frontiers, Antarctica delivers the paradox of needing to be protected from disturbance while requiring scientific endeavor to discover what is indigenous and learn how best to protect it. Moreover, like many natural environments on Earth, in Antarctica, microorganisms dominate the genetic pool and biomass of the colonizable niches and play the key roles in maintaining proper ecosystem function. This review puts into perspective insight that has been and can be gained about Antarctica's aquatic microbiota using molecular biology, and in particular, metagenomic approaches.

Sea–air CO2 flux in the North Atlantic subtropical gyre: Role and influence of Sub-Tropical Mode Water formation

The uptake of atmospheric carbon dioxide (CO2) into the mid-latitudes of the North Atlantic Ocean through the production of wintertime Sub-Tropical Mode Water (STMW) also known as Eighteen Degree Water (EDW) is poorly quantified and constrained. Nonetheless, it has been proposed that the EDW could serve as an important short-term sink of anthropogenic CO2. The objective of the present investigation was to determine sea–air CO2 gas exchange rates and seawater CO2 dynamics during wintertime formation of EDW in the North Atlantic Ocean. During 2006 and 2007, several research cruises were undertaken as part of the CLIMODE project across the northwest Atlantic Ocean with the intent to study the pre-conditioning, formation, and the evolution of EDW. Sea–air CO2 exchange rates were calculated based on measurements of atmospheric pCO2, surface seawater pCO2 and wind speed with positive values denoting a net flux from the surface ocean to the atmosphere. Average sea–air CO2 flux calculated along cruise tracks in the formation region equaled −18±6mmol CO2m−2d−1 and −14±9mmol CO2m−2d−1 in January of 2006 and March of 2007, respectively. Average sea–air CO2 flux in newly formed outcropping EDW in February and March of 2007 equaled −28±10mmol CO2m−2d−1. These estimates exceeded previous flux estimates in this region by 40–185%. The magnitude of CO2 flux was mainly controlled by the observed variability in wind speed and ΔpCO2 with smaller changes owing to variability in sea surface temperature. Small but statistically significant difference (4.1±2.6μmolkg−1) in dissolved inorganic carbon (DIC) was observed in two occurrences of newly formed EDW in February and March of 2007. This difference was explained either by differences in the relative contribution from different water masses involved in the initial formation process of EDW or temporal changes owing to sea–air CO2 exchange (∼25%) and vertical and/or lateral mixing (∼75%) with water masses high in DIC from the cold side of the Gulf Stream and/or from below the permanent thermocline. Based on the present estimate of sea–air CO2 flux in newly formed EDW and a formation rate of 9.3Svy (Sverdrup year=106m3s−1 flow sustained for 1 year), CO2 uptake by newly formed EDW may constitute 3–6% of the total North Atlantic CO2 sink. However, advection of surface waters that carry an elevated burden of anthropogenic CO2 that are transported to the formation region and transformed to mode water may contribute additional CO2 to the total net uptake and sequestration of anthropogenic CO2 to the ocean interior.

Carbon Mineralization: From Natural Analogues to Engineered Systems

Carbon mineralization sequesters CO2 by reaction of alkaline earth metal bearing silicate and hydroxide minerals with CO2 to form stable carbonate minerals. Seifritz (1990) proposed harnessing this natural process as a method for sequestration of anthropogenic CO2. It was first studied in detail as an industrial process by Lackner et al. (1995), which is often referred to as “mineral carbonation.” Much of this early research aimed to capitalize on the globally abundant natural deposits of ultramafic and mafic rocks, which are rich in alkaline earth metals, in addition to the long-term stability of the resultant carbonate minerals (Lackner et al. 1995). More recently, other process routes have been investigated that rely on feedstocks other than naturally occurring minerals (e.g., industrial wastes) as a source of cations for carbonate precipitation. Therefore, we use the more general term “carbon mineralization” to refer to any process that sequesters CO2 as a solid carbonate phase. The main advantages of carbon mineralization as a CO2 storage method are that the reactions are thermodynamically favored, the carbonation processes can be readily controlled and manipulated, and the resulting product is benign and stable over geological time. We begin this review with an overview of the fundamental processes that are relevant to carbon mineralization, which provides a basic framework in which to understand CO2 sequestration strategies based on carbon mineralization. We next discuss natural analogues to engineered systems, focusing on (1) exhumed hydrothermal systems in peridotite that have formed listvenite (magnesite + quartz) and soapstone and (2) shallow subsurface peridotite weathering processes and related alkaline springs that form carbonate veins, surficial travertine deposits, and hydromagnesite–magnesite playas. The propensity to form carbonate minerals in these ultramafic terranes reflects the thermodynamic instability of Mg-silicate minerals in the presence of CO2. …