Storage Of Atmospheric CO2 Research Articles

Establishing a Platform for Probing Reactive Carbon Capture in Ionic Liquids through Non-Aqueous Electrochemistry

The successful reactive carbon capture (RCC) and subsequent storage of atmospheric CO2 plays a pivotal role in advancing renewable energy and mitigating greenhouse gas emissions. Despite significant progress in reactor, catalyst, and microenvironment design in aqueous media, achieving optimal CO2 conversion efficiency, reproducibility, and selectivity in non-aqueous media remains a challenge. Promising strategies for developing pragmatic systems in anhydrous environments include controlling efficiency, selectivity, and reproducibility by enhancing local microenvironments of metallic surfaces with polymer overlayers and utilizing metallic surfaces to benchmark the RCC capability of ionic liquids. This research indicates that employing surfaces with bulk or trace metallic Pb is an ideal platform for exploring these strategies. Results show that in non-aqueous electrolytes we have successfully created an enhanced microenvironment on trace metallic Pb for selective CO2 conversion to oxalate on carbon supports. Notably, trace metallic Pb on the ppb scale demonstrates comparable faradaic efficiencies (FE), FEZnC2O4 ~ 84%, to bulk metallic Pb, FEZnC2O4 90%, from -2.1 to -1.8 V vs. Fc/Fc+ for the reductive coupling of CO2, and polymer encapsulation of trace Pb fosters an enhanced microenvironment promoting oxalate selectivity over CO. Furthermore, when polarized Pb electrodes are used in non-aqueous electrolytes containing ionic liquids there is a substantial shift in product selectivity from oxalate to more efficient CO production, allowing for the RCC capability of ionic liquids to be compared. The RCC capability of the ionic liquids can be compared as the shift in selectivity from oxalate to CO indicates a mechanistic change that only occurs in the presence of ionic liquids. The ionic liquids tested in this work include [EMIM][OTF], [EMIM][BF4], [EMIM]-[TFSI], and [EMIM][2-CNpyr]. Notably, [EMIM][2-CNpyr] had the most promising RCC capabilities as it exhibited no oxalate product and almost exclusively CO production (FECO~70%).

Ecosystem Services: A Social and Semantic Network Analysis of Public Opinion on Twitter.

Social media data reveal patterns of knowledge, attitudes, and behaviours of users on a range of topics. This study analysed 4398 tweets gathered between 17 January 2022 and 3 February 2022 related to ecosystem services, using the keyword and hashtag "ecosystem services". The Microsoft Excel plugin, NodeXL was used for social and semantic network analysis. The results reveal a loosely dense network in which information is conveyed slowly, with homogeneous, medium-sized subgroups typical of the community cluster structure. Citizens, NGOs, and governmental administrations emerged as the main gatekeepers of information in the network. Various semantic themes emerged such as the protection of natural capital for the sustainable production of ecosystem services; nature-based solutions to protect human structures and wellbeing against natural hazards; socio-ecological systems as the interaction between human beings and the environment; focus on specific services such as the storage of atmospheric CO2 and the provision of food. In conclusion, the perception of social users of the role of ecosystem services can help policymakers and forest managers to outline and implement efficient forest management strategies and plans.

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air.

Mitigation of anthropogenic climate change is expected to require large-scale deployment of carbon dioxide removal strategies. Prominent among these strategies is direct air capture with sequestration (DACS), which encompasses the removal and long-term storage of atmospheric CO2 by purely engineered means. Because it does not require arable land or copious amounts of freshwater, DACS is already attractive in the context of sustainable development, but opportunities to improve its sustainability still exist. Leveraging differences in the chemistry of CO2 and water adsorption within porous solids, here, the prospect of simultaneously removing water alongside CO2 in direct air capture operations is investigated. In many cases, the co-adsorbed water can be desorbed separately from chemisorbed CO2 molecules, enabling efficient harvesting of water from air. Depending upon the material employed and process conditions, the desorbed water can be of sufficiently high purity for industrial, agricultural, or potable use and can thus improve regional water security. Additionally, the recovered water can offset a portion of the costs associated with DACS. In this Perspective, molecular- and process-level insights are combined to identify routes toward realizing this nascent yet enticing concept.

Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands

Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO2 in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30–70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m−2 y−1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y−1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.

Adaptive multi-paddock grazing management's influence on soil food web community structure for: increasing pasture forage production, soil organic carbon, and reducing soil respiration rates in southeastern USA ranches.

BackgroundMeasurement of two grazing management’s influence on pasture productivity, soil food web structure, soil organic carbon and soil microbial respiration efficiency was conducted on five southeastern US, across-the-fence ranch pairs to compare adaptive multi-paddock grazing (AMP) management, using short grazing events with planned, adaptive recovery periods, to conventional grazing (CG) management, with continuous grazing at low stock density.MethodologyA point-in-time experimental field analysis was conducted to compare five AMP or CG ranch pairs to better understand the influence of grazing management on (a) standing crop biomass productivity; (b) soil food web community population, structure and functionality; (c) soil organic carbon accrual; and d) soil-C (CO2) respiration kinetics.ResultsAMP grazing systems outperformed CG systems by generating: (a) 92.68 g m−2 more standing crop biomass (SCB), promoting 46% higher pasture photosynthetic capacity (Two sample Mann-Whitney; Z = 6.1836; no DF in MW; p = 6.26 × 10−10; Effect size = 0.35) (b) a strong positive linear relationship of SCB with fungal biomass (R = 0.9915; F(1,3) = 175.35; p = 0.015); fungal to bacterial (F:B) biomass ratio (R = 0.9616; F(1,3) = 36.75; p = 0.009) and a soil food web proxy (R = 0.9616; F(1,3) = 36.75; p = 0.009) and a concurrent very strong inverse relationship with bacteria biomass (R = −0.946; F(1,3) = 25.56; p = 0.015); (c) significant predator/prey interactions with an inverse relationship with bacterial population biomass (R = − 0.946; F(1,3) = 25.56; p = 0.015) and a positive relationship with total protozoa enumeration (R = 0.9826; F(1,3) = 83.68; p = 0.003) when compared to SCB; (d) a 19.52% reduction in soil C (CO2) respiration rates (Two sample t-test; T = −2.3581; DF = 52.3541; p = 0.0221; Effect size = 0.59); and (e) a 20.6% increase in soil organic carbon (SOC) in the top 10 cm of soil profile (Two sample Mann–Whitney; Z = 2.6507; no DF in MW; p = 0.008; Effect size = 0.24). Rancher conversion to AMP grazing strategies would appear to regenerate soil food web population, structure, diversity and biological functionality helping to improve: carbon flow into plant biomass, buildup of soil carbon, predator/prey nutrient cycling and soil microbial respiration efficiency while offering improved climate resilience and a strategy to increase the capture and storage of atmospheric CO2 in soils of the world’s rangeland.

ASSESSING URBAN FOREST CANOPY COVER IN GREAT PLAIN CONSERVATION AREA (DÜZCE CITY, TURKEY) BETWEEN 1984 AND 2015

Abstract. Urban trees and forests are essential components of the urban environment. They can provide numerous ecosystem services and goods, including but not limited to recreational opportunities and aesthetic values, removal of air pollutants, improving air and water quality, providing shade and cooling effect, reducing energy use, and storage of atmospheric CO2. However, urban trees and forests have been in danger of being lost by dense housing resulting from population growth in the cities since the 1950s, leading to increased local temperature, pollution level, and flooding risk. Thus, determining the status of urban trees and forests is necessary for comprehensive understanding and quantifying the ecosystem services and goods. Tree canopy cover is a relatively quick, easy to obtain, and cost-effective urban forestry metric broadly used to estimate ecosystem services and goods of the urban forest. This study aimed to determine urban forest canopy cover areas and monitor the changes between 1984–2015 for the Great Plain Conservation area (GPCA) that has been declared as a conservation Area (GPCA) in 2017, located on the border of Düzce City (Western Black Sea Region of Turkey). Although GPCA is a conservation area for agricultural purposes, it consists of the city center with 250,000 population and most settlement areas. A random point sampling approach, the most common sampling approach, was applied to estimate urban tree canopy cover and their changes over time from historical aerial imageries. Tree canopy cover ranged from 16.0% to 27.4% within the study period. The changes in urban canopy cover between 1984–1999 and 1999–2015 were statistically significant, while there was no statistical difference compared to the changes in tree canopy cover between 1984–2015. The result of the study suggested that an accurate estimate of urban tree canopy cover and monitoring long-term canopy cover changes are essential to determine the current situation and the trends for the future. It will help city planners and policymakers in decision-making processes for the future of urban areas.

Operationalizing the net-negative carbon economy.

The remaining carbon budget for limiting global warming to 1.5 degrees Celsius will probably be exhausted within this decade1,2. Carbon debt3 generated thereafter will need to be compensated by net-negative emissions4. However, economic policy instruments to guarantee potentially very costly net carbon dioxide removal (CDR) have not yet been devised. Here we propose intertemporal instruments to provide the basis for widely applied carbon taxes and emission trading systems to finance a net-negative carbon economy5. We investigate an idealized market approach to incentivize the repayment of previously accrued carbon debt by establishing the responsibility of emitters for the net removal of carbon dioxide through ‘carbon removal obligations’ (CROs). Inherent risks, such as the risk of default by carbon debtors, are addressed by pricing atmospheric CO2 storage through interest on carbon debt. In contrast to the prevailing literature on emission pathways, we find that interest payments for CROs induce substantially more-ambitious near-term decarbonization that is complemented by earlier and less-aggressive deployment of CDR. We conclude that CROs will need to become an integral part of the global climate policy mix if we are to ensure the viability of ambitious climate targets and an equitable distribution of mitigation efforts across generations.

Impacts of land management practices on blue carbon stocks and greenhouse gas fluxes in coastal ecosystems-A meta-analysis.

Global recognition of climate change and its predicted consequences has created the need for practical management strategies for increasing the ability of natural ecosystems to capture and store atmospheric carbon. Mangrove forests, saltmarshes and seagrass meadows, referred to as blue carbon ecosystems (BCEs), are hotspots of atmospheric CO2 storage due to their capacity to sequester carbon at a far higher rate than terrestrial forests. Despite increased effort to understand the mechanisms underpinning blue carbon fluxes, there has been little synthesis of how management activities influence carbon stocks and greenhouse gas (GHG) fluxes in BCEs. Here, we present a global meta-analysis of 111 studies that measured how carbon stocks and GHG fluxes in BCEs respond to various coastal management strategies. Research effort has focused mainly on restoration approaches, which resulted in significant increases in blue carbon after 4years compared to degraded sites, and the potential to reach parity with natural sites after 7-17years. Lesser studied management alternatives, such as sediment manipulation and altered hydrology, showed only increases in biomass and weaker responses for soil carbon stocks and sequestration. The response of GHG emissions to management was complex, with managed sites emitting less than natural reference sites but emitting more compared to degraded sites. Individual GHGs also differed in their responses to management. To date, blue carbon management studies are underrepresented in the southern hemisphere and are usually limited in duration (61% of studies <3years duration). Our meta-analysis describes the current state of blue carbon management from the available data and highlights recommendations for prioritizing conservation management, extending monitoring time frames of BCE carbon stocks, improving our understanding of GHG fluxes in open coastal systems and redistributing management and research effort into understudied, high-risk areas.

Marine Metabolomics: a Method for Nontargeted Measurement of Metabolites in Seawater by Gas Chromatography-Mass Spectrometry.

Microbial communities exchange molecules with their environment, which plays a major role in regulating global biogeochemical cycles and climate. While extracellular metabolites are commonly measured in terrestrial and limnic ecosystems, the presence of salt in marine habitats limits the nontargeted analyses of the ocean exometabolome using mass spectrometry (MS). Current methods require salt removal prior to sample measurements, which can alter the molecular composition of the metabolome and limit the types of compounds detected by MS. To overcome these limitations, we developed a gas chromatography MS (GC-MS) method that avoids sample altering during salt removal and that detects metabolites down to nanomolar concentrations from less than 1 ml of seawater. We applied our method (SeaMet) to explore marine metabolomes in vitro and in vivo First, we measured the production and consumption of metabolites during the culture of a heterotrophic bacterium, Marinobacter adhaerens Our approach revealed successional uptake of amino acids, while sugars were not consumed. These results show that exocellular metabolomics provides insights into nutrient uptake and energy conservation in marine microorganisms. We also applied SeaMet to explore the in situ metabolome of coral reef and mangrove sediment porewaters. Despite the fact that these ecosystems occur in nutrient-poor waters, we uncovered high concentrations of sugars and fatty acids, compounds predicted to play a key role for the abundant and diverse microbial communities in coral reef and mangrove sediments. Our data demonstrate that SeaMet advances marine metabolomics by enabling a nontargeted and quantitative analysis of marine metabolites, thus providing new insights into nutrient cycles in the oceans.IMPORTANCE Nontargeted approaches using metabolomics to analyze metabolites that occur in the oceans is less developed than those for terrestrial and limnic ecosystems. One of the challenges in marine metabolomics is that salt limits metabolite analysis in seawater to methods requiring salt removal. Building on previous sample preparation methods for metabolomics, we developed SeaMet, which overcomes the limitations of salt on metabolite detection. Considering that the oceans contain the largest dissolved organic matter pool on Earth, describing the marine metabolome using nontargeted approaches is critical for understanding the drivers behind element cycles, biotic interactions, ecosystem function, and atmospheric CO2 storage. Our method complements both targeted marine metabolomic investigations as well as other "omics" (e.g., genomics, transcriptomics, and proteomics) approaches by providing an avenue for studying the chemical interaction between marine microbes and their habitats.

Precession modulation of the South Pacific westerly wind belt over the past million years

The southern westerly wind belt (SWW) interacts with the Antarctic Circumpolar Current and strongly impacts the Southern Ocean carbon budget, and Antarctic ice-sheet dynamics across glacial-interglacial cycles. We investigated precipitation-driven sediment input changes to the Southeast Pacific off the southern margin of the Atacama Desert over the past one million years, revealing strong precession (19/23-ka) cycles. Our simulations with 2 ocean-atmosphere general circulation models suggest that observed cyclic rainfall changes are linked to meridional shifts in water vapor transport from the tropical Pacific toward the southern Atacama Desert. These changes reflect a precessional modulation of the split in the austral winter South Pacific jet stream. For precession maxima, we infer significantly enhanced rainfall in the southern Atacama Desert due to a stronger South Pacific split jet with enhanced subtropical/subpolar jets, and a weaker midlatitude jet. Conversely, we derive dry conditions in northern Chile related to reduced subtropical/subpolar jets and an enhanced midlatitude jet for precession minima. The presence of precessional cycles in the Pacific SWW, and lack thereof in other basins, indicate that orbital-scale changes of the SWW were not zonally homogeneous across the Southern Hemisphere, in contrast to the hemispherewide shifts of the SWW suggested for glacial terminations. The strengthening of the jet is unique to the South Pacific realm and might have affected winter-controlled changes in the mixed layer depth, the formation of intermediate water, and the buildup of sea-ice around Antarctica, with implications for the global overturning circulation and the oceanic storage of atmospheric CO2.

Investigating Particle Size-Flux Relationships and the Biological Pump Across a Range of Plankton Ecosystem States From Coastal to Oligotrophic

Sinking particles transport organic carbon produced in the surface ocean to the ocean interior, leading to net storage of atmospheric CO2 in the deep ocean. The rapid growth of in situ imaging technology has the potential to revolutionize our understanding of particle flux attenuation in the ocean; however, estimating particle flux from particle size and abundance (measured directly by in situ cameras) is challenging. Sinking rates are dependent on several factors, including particle excess density and porosity, which vary based on particle origin and type. Additionally, particle characteristics are transformed while sinking. We compare optically-measured particle size spectra profiles (Underwater Vision Profiler 5, UVP) with contemporaneous measurements of particle flux made using sediment traps and 234Th:238U disequilibrium on six process cruises from the California Current Ecosystem (CCE) LTER Program. These measurements allow us to assess the efficacy of using size-flux relationships to estimate fluxes from optical particle size measurements. We find that previously published parameterizations that estimate carbon flux from UVP profiles are a poor fit to direct flux measurements in the CCE. This discrepancy is found to result primarily from the important role of fecal pellets in particle flux. These pellets are primarily in a size range (i.e., 100 – 400 µm) that is not well-resolved as images by the UVP due to the resolution of the sensor. We develop a new, CCE-optimized algorithm for estimating carbon flux from UVP data in the southern California Current (Flux = ∑_(i=1)^x▒〖n_i A〖d_i〗^B ∆d_i 〗), with A = 13.45, B = 1.35, d = particle diameter (mm) and Flux in units of mg C m-2 d-1. We caution, however, that increased accuracy in flux estimates derived from optical instruments will require devices with greater resolution, the ability to differentiate fecal pellets from low porosity marine snow aggregates, and improved sampling of rapidly sinking fecal pellets. We also find that the particle size-flux relationships may be different within the euphotic zone than in the shallow twilight zone and hypothesize that the changing nature of sinking particles with depth must be considered when investigating the remineralization length scale of sinking particles in the ocean.

Controlling factors of organic carbon stocks in agricultural topsoils and subsoils of Bavaria

Agricultural soils are highly important organic carbon (OC) reservoirs in Central Europe. Their OC stocks are crucial for a wide range of ecosystem services such as food security or climate regulation through atmospheric CO2 storage. There is increasing evidence that the controlling factors of OC stocks may differ between topsoil and subsoil, but distinct knowledge about the factors at a regional scale for temperate soils is scarce. In order to identify the controlling factors of OC storage in agricultural soils we implemented a random forest model on a data set of 692 soil profiles located in Bavaria, Southeast Germany. We differentiated between topsoil (0–30 cm profile depth) and subsoil (30–100 cm) and predicted OC stocks (kg OC m−2) using 13 predictor variables including soil type, topographical factors, climatic factors and information on land use. The explained variance of the topsoil random forest was higher than that of the subsoil (51 and 23%, respectively). The fact that major proportions of the variance in the modelling of subsoil OC remained unexplained, revealed high uncertainties that persist about subsoil OC storage. OC storage of both, topsoils and subsoils, was to a large extend determined by four factors: land use history, soil type, major landform and topographic wetness index (TWI). Climatic factors as well as clay content had surprisingly low impact on the model. Topsoil OC was mainly controlled by the legacy of the land use resulting in highest stocks under permanent grassland use. In contrast, soil type and topographical factors, i.e. major landform and TWI, largely determined subsoil OC stocks. The topography indicates the lateral transport of OC due to soil erosion and its subsequent deposition in low lying landform positions. There, high soil moisture as indicated by the TWI, hampers the decomposition of the OC. Human activities such as tillage amplify the lateral OC transport and therefore the amount of buried OC. As a result of these processes, highest subsoil stocks were found in alluvial, colluvial and groundwater affected soils. The findings demonstrate the close link between the generic soil type, topography, land use and OC stocks. We further conclude that the legacy of human activities affect both, topsoil and subsoil OC storage.

Effects of soil process formalisms and forcing factors on simulated organic carbon depth-distributions in soils

Soil organic carbon (OC) sequestration (i.e. the capture and long-term storage of atmospheric CO2) is being considered as a possible solution to mitigate climate change, notably through land use change (conversion of cropped land into pasture) and conservation agricultural practices (reduced tillage). Subsoil horizons (from 30 cm to 1 m) contribute to ca. half the total amount of soil OC, and the slow dynamics of deep OC as well as the relationships between the OC depth distribution and changes in land use and tillage practices still need to be modelled.We developed a fully modular, mechanistic OC depth distribution model, named OC-VGEN. This model includes OC dynamics, plant development, transfer of water, gas and heat, mixing by bioturbation and tillage as processes and climate and land use as boundary conditions. OC-VGEN allowed us to test the impact of 1) different numerical representations of root depth distribution, decomposition coefficients and bioturbation; 2) evolution of forcing factors such as land use, agricultural practices and climate on OC depth distribution at the century scale.We used the model to simulate decadal to century time scale experiments in Luvisols with different land uses (pasture and crop) and tillage practices (conventional and reduced) as well as projection scenarios of climate and land use at the horizon of 2100. We showed that, among the different tested formalisms/parametrizations: 1) the sensitivity of the simulated OC depth distribution to the tested numerical representations depended on the considered land use; 2) different numerical representations may accurately fit past soil OC evolution while leading to different OC stock predictions when tested for future forcing conditions (change of land use, tillage practice or climate).

Climate Stability and Fossil Carbon-Based Energy Production—Unbreakable Opposites? Theses for an Attempt to Systematically Describe the Science of Overcoming Climate Change

Recognizing climate change as a consequence of rising atmospheric CO2 concentration, due to massive use of fossil carbon for energy production, has resulted in the need to find alternative sources for energy supply independent from carbon. Success has been poor, and consumption of fossil carbon is rising. Hence, CO2 concentration in the atmosphere is increasing, exacerbating climate change. So the question is: what can be done to change this situation so that energy supply remains abundant but climate is not endangered? Biotechnology is appropriate to control atmospheric CO2 concentration, which is the result of natural CO2 movement, technically performed liberation of CO2 from fossil materials, and biologically driven capture of CO2 out of the atmosphere. In this work, basic considerations are made and formulated to elucidate carbon behavior as well as carbon use in relation to its action on climate. Conclusions are drawn considering CO2 in its dual function as waste of energy production and raw material for energy-containing products, suggesting introduction of CO2 waste management, suggesting introduction of global CO2 monitoring, suggesting revision of the connections between industry and agriculture, forestry and aquaculture (AFA), and considering growth of plants on oceanic surface as well as storage of plant residuals on oceanic floor as voluminous reserves for uptake and storage of atmospheric CO2 enabling regulation of climate development.

Canadian urban tree canopy cover and carbon sequestration status and change 1990–2012

Urban trees provide numerous ecosystem goods and services by providing shade, habitat for wildlife, removal of air pollutants and the removal and storage of atmospheric CO2. Carbon removal services provided by Canadian urban trees have previously been assessed using an IPCC 2006 guidelines approach based on the percentage of urban area covered by tree canopy (UTC) for the 2012 time period (Pasher et al., 2014). That work however provided only a single point in time assessment of the national scale UTC and carbon removal services. The research undertaken for this study was a continuation of this earlier work focusing on a 1990 national scale UTC assessment and carbon sequestration estimates for 1990. UTC estimates for 1990 were developed using a point sampling approach with circa 1990 air photos covering a large portion of Canadian urban areas. In total almost 179,000 points were sampled for the 1990 time period, reassessing 83% of the points used for the previous 2012 assessment. Based on the urban area boundary layers for 1991 and 2011, Canada’s urban areas grew by an estimated 6% for this time period. Most of this growth occurred through conversion of agricultural and forested lands to urban. At the national scale the UTC for 1990 was estimated to be 27.6%, as compared to the 2012 UTC estimate of 26.1%, the difference between estimates for the two time periods fell within the uncertainty range. Carbon removal estimates based on the UTC estimates were also very similar for the two dates with 660.2 kt C removed in 1990 and 662.8 kt C removed in 2012. It was noted that urban development in the Prairie regions resulted in an increase in tree cover as compared to the pre-conversion agricultural and natural landscapes and also that in most urban areas across the country UTC increases through time as tree cover matured in newly developed urban areas. These two assessments provide a time series of urban trees for 22 year time period, which will be useful for further studies and analysis.

Deciphering ocean carbon in a changing world

Dissolved organic matter (DOM) in the oceans is one of the largest pools of reduced carbon on Earth, comparable in size to the atmospheric CO2 reservoir. A vast number of compounds are present in DOM, and they play important roles in all major element cycles, contribute to the storage of atmospheric CO2 in the ocean, support marine ecosystems, and facilitate interactions between organisms. At the heart of the DOM cycle lie molecular-level relationships between the individual compounds in DOM and the members of the ocean microbiome that produce and consume them. In the past, these connections have eluded clear definition because of the sheer numerical complexity of both DOM molecules and microorganisms. Emerging tools in analytical chemistry, microbiology, and informatics are breaking down the barriers to a fuller appreciation of these connections. Here we highlight questions being addressed using recent methodological and technological developments in those fields and consider how these advances are transforming our understanding of some of the most important reactions of the marine carbon cycle.

Ocean acidification alters the calcareous microstructure of the green macro-alga Halimeda opuntia

Decreases in seawater pH and carbonate saturation state (Ω) following the continuous increase in atmospheric CO2 represent a process termed ocean acidification, which is predicted to become a main threat to marine calcifiers in the near future. Segmented, tropical, marine green macro-algae of the genus Halimeda form a calcareous skeleton that involves biotically initiated and induced calcification processes influenced by cell physiology. As Halimeda is an important habitat provider and major carbonate sediment producer in tropical shallow areas, alterations of these processes due to ocean acidification may cause changes in the skeletal microstructure that have major consequences for the alga and its environment, but related knowledge is scarce. This study used scanning electron microscopy to examine changes of the CaCO3 segment microstructure of Halimeda opuntia specimens that had been exposed to artificially elevated seawater pCO2 of ~650 µatm for 45 d. In spite of elevated seawater pCO2, the calcification of needles, located at the former utricle walls, was not reduced as frequent initiation of new needle-shaped crystals was observed. Abundance of the needles was ~22 % µm−2 higher and needle crystal dimensions ~14 % longer. However, those needles were ~42 % thinner compared with the control treatment. Moreover, lifetime cementation of the segments decreased under elevated seawater pCO2 due to a loss in micro-anhedral carbonate as indicated by significantly thinner calcified rims of central utricles (35–173 % compared with the control treatment). Decreased micro-anhedral carbonate suggests that seawater within the inter-utricular space becomes CaCO3 undersaturated (Ω < 1) during nighttime under conditions of elevated seawater pCO2, thereby favoring CaCO3 dissolution over micro-anhedral carbonate accretion. Less-cemented segments of H. opuntia may impair the environmental success of the alga, its carbonate sediment contribution, and the temporal storage of atmospheric CO2 within Halimeda-derived sediments.

CO2 hydrate formation and dissociation rates: Application to Mars

CO2 clathrate hydrate is a crystalline material composed of water cages around a CO2 molecule. CO2 gas hydrates are naturally occurring on Earth and are a likely phase on Mars as well as other cold planetary bodies. CO2 hydrates have minor effects on terrestrial atmospheric composition, but may be a major reservoir for greenhouse gases on Mars. In this study, CO2 hydrate formation and dissociation rates were measured experimentally on ultrapure and CO2 infused water ice (ice containing previously trapped CO2 gas bubbles). Overall, increasing pressure and temperature increased CO2 consumption rates, indicating enhanced hydrate formation rates. CO2 consumption and release rates both increased significantly in infused ice experiments as did the overall amount of CO2 consumed. CO2 bubbles formed during freezing of the infused ice likely provided more surface area for hydrate nucleation, increasing the rate of formation. Higher dissociation rates in infused ice experiments compared to ultrapure ice may be due to the higher concentration of hydrate originally formed in the bubble-filled samples. These results suggest that CO2 hydrate formation in natural, gas-rich ice occurs significantly faster than previously assumed. In addition, formation rates would be maximized and dissociation rates minimized at Mars equatorial conditions, perhaps leading to long-term storage of atmospheric CO2 in localized clathrate reservoirs.

Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing

The ocean's role in regulating atmospheric carbon dioxide on glacial‐interglacial timescales remains an unresolved issue in paleoclimatology. Reduced mixing between deep water masses may have aided oceanic storage of atmospheric CO2 during the Last Glacial Maximum (LGM), but data supporting this idea have remained elusive. The δ13C of benthic foraminifera indicate the Atlantic Ocean was more chemically stratified during the LGM, but the nonconservative nature of δ13C complicates interpretation of the LGM signal. Here we use benthic foraminiferal δ18O as a conservative tracer to constrain the ratio of meridional transport to vertical diffusivity in the deep Atlantic. Our calculations suggest that the ratio was at least twice as large at the LGM. We speculate that the primary cause was reduced mixing between northern and southern component waters, associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor. The shallower water mass boundary yields an order of magnitude increase in the volume of southern component water, suggesting its residence time may have increased substantially. Our analysis supports the idea that an expanded volume of Antarctic Bottom Water and limited vertical mixing enhanced the abyssal ocean's ability to trap carbon during glacial times.

Competing roles of rising CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and climate change in the contemporary European carbon balance

Abstract. Natural ecosystems respond to, and may affect climate change through uptake and storage of atmospheric CO2. Here we use the land-surface and carbon cycle model JULES to simulate the contemporary European carbon balance and its sensitivity to rising CO2 and changes in climate. We find that the impact of climate change is to decrease the ability of Europe to store carbon by 97 TgC yr−1. In contrast, the effect of rising atmospheric CO2 has been to stimulate increased uptake and storage. The CO2 effect is currently dominant leading to a net increase of 114 TgC yr−1. Our simulations do not at present include other important factors such as land use and management, the effects of forest age classes and nitrogen deposition. Understanding this balance and its implications for mitigation policies is becoming increasingly important.