Ocean Alkalinity Enhancement (OAE) is a Negative Emissions Technology (NET) that shows significant potential for climate change mitigation. By increasing the bicarbonate ion concentration in ocean water, OAE could enhance long-term carbon storage and mitigate ocean acidification. However, the side effects and/or potential co-benefits of OAE on natural planktonic communities remain poorly understood. To address this knowledge gap, a mesocosm experiment was conducted in the oligotrophic waters of Gran Canaria. A CO2-equilibrated Total Alkalinity (TA) gradient was employed in increments of 300 µmol·L-1, ranging from ~2400 to ~4800 µmol·L-1. This study represents the first attempt to evaluate the potential impacts of OAE on planktonic communities under natural conditions. The results show that Net Community Production (NCP), Gross Production (GP), Community Respiration (CR) rates, as well as the metabolic balance (GP:CR), did not exhibit a linear response to the whole alkalinity gradient. Instead, significant polynomial and linear regression models were observed for all rates up to ∆TA1800 µmol·L-1, in relation to the Dissolved Inorganic Carbon (DIC) concentrations. Notably, the ∆TA1500 and 1800 µmol·L-1 treatments showed peaks in NCP shifting from a heterotrophic to an autotrophic state, with NCP values of 4 and 8 µmol O2 kg-1 d-1, respectively. These peaks and the optimum curve were also reflected in the nanophytoplankton abundance, size-fractionated chlorophyll a and 14C uptake data. Furthermore, abiotic precipitation occurred in the highest treatment after day 21 but no impact on the measured parameters was detected. Overall, a damaging effect of CO2-equilibrated OAE in the range applied here, on phytoplankton primary production, community metabolism and composition could not be inferred. In fact, a potential co-benefit to OAE was observed in the form of the positive curvilinear response to the DIC gradient up to the ∆TA1800 treatment. Further experimental research at this scale is key to gain a better understanding of the short and long-term effects of OAE on planktonic communities.
Continue reading ‘Assessing the impact of CO2 equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system’Posts Tagged 'mitigation'
Assessing the impact of CO2 equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system
Published 25 October 2023 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, mesocosms, mitigation, North Pacific, otherprocess, photosynthesis, phytoplankton, primary production, prokaryotes, respiration
Oyster reefs’ control of carbonate chemistry—Implications for oyster reef restoration in estuaries subject to coastal ocean acidification
Published 12 October 2023 Science ClosedTags: abundance, algae, biological response, calcification, chemistry, field, mitigation, mollusks, morphology, mortality, North Atlantic, otherprocess
Globally, oyster reef restoration is one of the most widely applied coastal restoration interventions. While reefs are focal points of processes tightly linked to the carbonate system such as shell formation and respiration, how these processes alter reef carbonate chemistry relative to the surrounding seawater is unclear. Moreover, coastal systems are increasingly impacted by coastal acidification, which may affect reef carbonate chemistry. Here, we characterized the growth of multiple constructed reefs as well as summer variations in pH and carbonate chemistry of reef-influenced seawater (in the middle of reefs) and ambient seawater (at locations ~50 m outside of reefs) to determine how reef chemistry was altered by the reef community and, in turn, impacts resident oysters. High frequency monitoring across three subtidal constructed reefs revealed reductions of daily mean and minimum pH (by 0.05–0.07 and 0.07–0.12 units, respectively) in seawater overlying reefs relative to ambient seawater (p < .0001). The proportion of pH measurements below 7.5, a threshold shown to negatively impact post-larval oysters, were 1.8×–5.2× higher in reef seawater relative to ambient seawater. Most reef seawater samples (83%) were reduced in total alkalinity relative to ambient seawater samples, suggesting community calcification was a key driver of modified carbonate chemistry. The net metabolic influence of the reef community resulted in reductions of CaCO3 saturation state in 78% of discrete samples, and juvenile oysters placed on reefs exhibited slower shell growth (p < .05) compared to oysters placed outside of reefs. While differences in survival were not detected, reef oysters may benefit from enhanced survival or recruitment at the cost of slowed growth rates. Nevertheless, subtidal restored reef communities modified seawater carbonate chemistry in ways that likely increased oyster vulnerability to acidification, suggesting that carbonate chemistry dynamics warrant consideration when determining site suitability for oyster restoration, particularly under continued climate change.
Continue reading ‘Oyster reefs’ control of carbonate chemistry—Implications for oyster reef restoration in estuaries subject to coastal ocean acidification’Investigating the effect of silicate and calcium based ocean alkalinity enhancement on diatom silicification
Published 29 September 2023 Science ClosedTags: biological response, field, mesocosms, mitigation, North Atlantic, physiology, phytoplankton
Gigatonne-scale atmospheric carbon dioxide removal (CDR) will almost certainly be needed to supplement the emission reductions required to keep global warming between 1.5–2 °C. Ocean alkalinity enhancement (OAE) is an emerging marine CDR method with the addition of pulverized minerals to the surface ocean being one widely considered approach. A concern of this approach is the potential for dissolution products released from minerals to impact phytoplankton communities. We conducted an experiment with 10 pelagic mesocosms (M1–M10) in Raunefjorden, Bergen, Norway to assess the implications of simulated silicate- and calcium-based mineral OAE on a coastal plankton community. Five mesocosms (M1, M3, M5, M7 and M9) were enriched with silicate (~75 µmol L-1 Na2SiO3), alkalinity along a gradient from 0 to ~600 µmol kg-1, and magnesium in proportion to alkalinity additions. The other five mesocosms (M2, M4, M6, M8, M10) were enriched with alkalinity along the same gradient and calcium in proportion to alkalinity additions. The experiment explored many components of the plankton community, from microbes to fish larvae, and here we report on the influence of mineral based OAE on diatom silicification. Macronutrients (nitrate and phosphate) limited silicification at the onset of the experiment until nutrient additions on day 26. Silicification was significantly greater in the silicate-based mineral treatments, with silicate concentrations limiting silicification in the calcium-based treatment. The degree of silicification varied significantly between genera, and genera specific silicification also varied significantly between alkalinity mineral sources, with the exception of Cylindrotheca. Pseudo-nitzschia was the only genus affected by alkalinity, whereby silicification increased with increasing alkalinity during some periods of the experiment. No other genera displayed significant changes in silicification as a result of alkalinity increases between 0 and 600 µmol kg-1 above natural levels. Nor did we observe any indication of interactive effects between simulated mineral dissolution products and changes in carbonate chemistry. Previous experiments have provided evidence of alkalinity effects on diatoms underscoring the necessity for further studies under a range of boundary/environmental conditions to extract a more robust pattern of diatom responses to OAE. In summary, our findings suggest limited genus-specific impacts of alkalinity on diatoms, while also highlighting the importance of understanding the full breadth of different OAE approaches, their risks, co-benefits, and potential for interactive effects.
Continue reading ‘Investigating the effect of silicate and calcium based ocean alkalinity enhancement on diatom silicification’Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments
Published 19 September 2023 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, laboratory, mitigation, North Pacific, otherprocess, physiology, prokaryotes, sediment
Microbial iron reduction is a crucial process in natural ecosystems, contributing to the cycling of elements and supporting the biological activities of organisms. However, the significance of fermentative iron reduction in marine environments and microbial metabolism remains understudied compared with iron reduction coupled with respiration. The main objective of our study was to investigate the influence of fermentative iron reduction on microbial populations and marine sediment. Our findings revealed a robust iron-reducing activity in the enriched marine sediment, demonstrating a maximum ferrihydrite-reducing rate of 0.063 mmol/h. Remarkably, ferrihydrite reduction exhibited an intriguing pH-buffering effect through the release of OH+ and Fe2+ ions, distinct from fermentation alone. This effect resulted in substantial improvements in glucose consumption (71.4%), bacterial growth (48.1%), and metabolite production (80.8%). To further validate the acidification-buffering and metabolism-promoting effects of ferrihydrite reduction, we conducted iron-reducing experiments using a pure strain, Clostridium pasteurianum DMS525. The observed pH-buffering effect resulted from microbial iron reduction in marine sediment and has potential environmental implications by reducing CO2 emissions, mitigating acidification, and preserving the delicate balance of marine ecosystems.
Continue reading ‘Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments’Ocean acidification in the Philippines and the potential role of water pollution management in mitigating an unaddressed threat
Published 10 August 2023 Science ClosedTags: mitigation, policy, South Pacific
Ocean acidification is a major threat to marine ecosystems. It is caused by increasing carbon dioxide concentrations in the atmosphere due to anthropogenic emissions and has socio-ecological and socio-economic ramifications for many countries. However, in some critical areas like the Philippines, a known center of marine biodiversity, no legislation currently exists to manage it. This could be due to lack of understanding of the problem, conflicting priorities, or difficulties in implementation common to many developing countries. We consider a possible incremental pathway for the mitigation of ocean acidification impacts on Philippine marine ecosystems using existing laws on marine pollution. This could complement longer term efforts to formalize legislation and institutionalize efforts to address its effects in the country. The approach may possibly be applied in other areas where no specific legislation exists to address crucial environmental problems.
Continue reading ‘Ocean acidification in the Philippines and the potential role of water pollution management in mitigating an unaddressed threat’Laboratory experiments in ocean alkalinity enhancement research
Published 20 July 2023 Science ClosedTags: chemistry, laboratory, methods, mitigation
Recent concern about the consequences of continuing increases in atmospheric CO2 as a key heat-trapping agent (USGCRP, 2017; IPCC, 2021) have prompted ocean experts to come together to discuss how to provide science-based solutions. Ocean alkalinity enhancement (OAE) is being considered not only as a ocean carbon dioxide removal (CDR) approach, but also as a potential way to mitigate ocean acidification. Over the last two decades, inter-laboratory comparisons have proven valuable in evaluating the reliability of methodologies associated with sampling and analysis of carbonate chemistry parameters, which have been routinely used in ocean acidification research (Bockmon and Dickson, 2015). Given the complexity of processes and mechanisms related to ecosystem responses to OAE, consolidating protocols to ensure compatibility across studies is fundamental for synthesis and upscaling analysis. This chapter provides an overview of best practice in OAE laboratory experimentation and facilitates awareness of the importance of applying standardized methods to promote data re- use, inter-lab comparisons, and transparency. This chapter provides the reader with the tools to (1) identify the criteria to achieve the best laboratory practice and experimental design; (2) provide guidance on the selection of response variables for various purposes (physiological, biogeochemical, ecological, evolutionary) for inter-lab comparisons; (3) offer recommendation for a minimum set of variables that should be sampled and propose additional variables critical for different types of synthesis and upscaling; and (4) identify protocols for standardized measurements of response variables.
Continue reading ‘Laboratory experiments in ocean alkalinity enhancement research’The potential role of Posidonia oceanica for mitigating acidification on coastal waters of Europe
Published 12 July 2023 Science ClosedTags: biogeochemistry, biological response, chemistry, field, Mediterranean, mitigation, phanerogams, review
Ocean acidification is a major environmental concern that has significant ecological., economic, and social implications. The plantation and restoration of seagrass meadows in coastal waters, specifically Posidonia oceanica, is one possible method to combat ocean acidification and has the potential to have a significant positive impact on the marine environment and the overall state of the biosphere. As there has been a decline of Posidonia oceanica of about 30% in the Mediterranean Sea over the past three decades to about 1.2 mio ha in the Mediterranean Sea, the positive effects of the sea grass have diminished due to anthropogenic influence. Still, its importance as a carbon sink should not be underestimated. By using recent literature and different studies that have been analysed of the capacity of sea grass to mitigate the impacts of ocean acidification and the effects on the marine ecosystems, supported by several experiments that have been conducted, this thesis demonstrated the importance of Posidonia oceanica. The experiments showed that seagrass ecosystems have higher pH than ecosystems without seagrass, with a mean difference of 0.43. As the pH is interlocked with the CO2-levels and the oxygen levels, also experiments on these factors have been conducted. In general, the concentration of oxygen with P. oceanica present is 2mg/L higher than without. Equally, the CO2 concentration was lower with P. oceanica present. The Posidonia oceanica meadows present in the Mediterranean Sea are able to fixate about 13,3 mio tons of CO2, which is equal to 0,3% of Europeans CO2 emissions. About 2,8 mio tons of CO2 are sequestered by the sea grass, which is about 0,07% of European CO2 emissions. Furthermore, recent plantation efforts show the successful restoration of seagrass meadows and their overall benefits for the regional environment. Overall, this paper provides valuable insights into the potential role of seagrass meadows in mitigating ocean acidification and improving marine biosystems while providing specific numbers to support its findings.
Continue reading ‘The potential role of Posidonia oceanica for mitigating acidification on coastal waters of Europe’Mesocosm experiments in ocean alkalinity enhancement research
Published 12 July 2023 Science ClosedTags: methods, mitigation
An essential prerequisite for the implementation of ocean alkalinity enhancement (OAE) applications is their environmental safety. Only if it can be ensured that ecosystem health and ecosystem services are not at risk will the implementation of OAE move forward. Public opinion on OAEs will depend first and foremost on reliable evidence that no harm will be done to marine ecosystems and licensing authorities will demand measurable criteria against which environmental sustainability can be determined. In this context mesocosm experiments represent a highly valuable tool in determining the safe operating space of OAE applications. By combining realism and biological complexity with controllability and replication they provide an ideal OAE test bed and a critical stepping stone towards field applications. Mesocosm approaches can also be helpful in testing the efficacy, efficiency and permanence of OAE applications. This chapter outlines strengths and weaknesses of mesocosm approaches, illustrates mesocosm facilities and suitable experimental designs presently employed in OAE research, describes critical steps in mesocosm operation, and discusses possible approaches for alkalinity manipulation and monitoring. Building on a general treatise on each of these aspects, the chapter describes pelagic and benthic mesocosm approaches separately, given their inherent differences. The chapter concludes with recommendations for best practices in OAE-related mesocosm research.
Continue reading ‘Mesocosm experiments in ocean alkalinity enhancement research’Seawater carbonate system considerations for ocean alkalinity enhancement research
Published 12 July 2023 Science ClosedTags: chemistry, methods, mitigation
Ocean alkalinity enhancement (OAE) is a proposed marine carbon dioxide removal (mCDR) approach that has the potential for large-scale uptake of significant amounts of atmospheric carbon dioxide (CO2). Removing anthropogenic legacy CO2 will be required to stabalise global surface temperatures below the 1.5–2 °C Paris Agreement target of 2015. In this chapter we describe the impacts of various OAE feedstocks on seawater carbonate chemistry, as well as pitfalls that need to be avoided during sampling, storage and measurement of the four main carbonate chemistry parameters, i.e. dissolved inorganic carbon (DIC), total alkalinity (TA), pH and CO2 fugacity (fCO2). Finally, we also discuss considerations in regard to calculating carbonate chemistry speciation from two measured parameters.
Continue reading ‘Seawater carbonate system considerations for ocean alkalinity enhancement research’Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?
Published 20 June 2023 Science ClosedTags: biogeochemistry, biological response, growth, laboratory, mitigation, North Pacific, physiology, phytoplankton, primary production
It is increasingly apparent that adequately mitigating anthropogenic climate interference will require ocean carbon dioxide removal (CDR) strategies. Ocean alkalinity enhancement (OAE) is an abiotic ocean CDR approach that aims to increase the ocean’s CO2 uptake capacity through the dispersal of pulverized mineral or dissolved alkali into the surface ocean. However, OAE’s effect on marine biota is largely unexplored. Here, we investigate the impacts of moderate (~700 μmol kg−1) and high (~2700 μmol kg−1) limestone-inspired alkalinity additions on two biogeochemically and ecologically important phytoplankton functional group representatives: Emiliania huxleyi (calcium carbonate producer) and Chaetoceros sp. (silica producer). The growth rate and elemental ratios of both taxa showed a neutral response to limestone-inspired alkalinization. While our results are encouraging, we also observed abiotic mineral precipitation, which removed nutrients and alkalinity from solution. Our findings offer an evaluation of biogeochemical and physiological responses to OAE and provide evidence supporting the need for continued research into how OAE strategies affect marine ecosystems.
Continue reading ‘Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?’Broaden research on ocean alkalinity enhancement to better characterize social impacts
Published 15 June 2023 Science ClosedTags: mitigation, review, socio-economy
Ocean alkalinity enhancement (OAE) is being considered as a way of achieving large-scale removals of carbon dioxide from the atmosphere. Research on the risks and benefits of different OAE approaches is expanding apace, but it remains difficult to anticipate and appraise the potential impacts to human communities that OAE might generate. These impacts, however, will be critical to evaluating the viability of specific OAE projects. This paper draws on the authors’ involvement in interdisciplinary assessment of OAE (1) to identify the factors that currently limit characterization of potential social impacts and (2) to propose ways of reconfiguring OAE research to better consider these.
Severe 21st-century ocean acidification demands continuance and expansion of Antarctic Marine Protected Areas
Published 14 June 2023 Science ClosedTags: Antarctic, chemistry, mitigation, modeling, regionalmodeling
Antarctic coastal waters are home to several established or proposed Marine Protected Areas (MPAs) supporting exceptional biodiversity, which is threatened by anthropogenic climate change. Despite a particular sensitivity to ocean acidification (OA), little is known about the future carbonate chemistry of high-latitude Southern Ocean waters. Here, we use a high resolution ocean–sea ice–biogeochemistry model with realistic ice-shelf geometry to investigate 21st-century OA in Antarctic MPAs under four emission scenarios. By 2100, we project surface pH declines of up to 0.42 (total scale), corresponding to a 161% increase in hydrogen ion concentration relative to the 1990s. End-of-century aragonite undersaturation is ubiquitous across MPAs under the three highest emission scenarios. Vigorous vertical mixing of anthropogenic carbon on the continental shelves produces severe OA within the Weddell Sea, East Antarctic, and Ross Sea MPAs. Our findings call for continuity and expansion of Antarctic MPAs to reduce pressures on ecosystem integrity.
Continue reading ‘Severe 21st-century ocean acidification demands continuance and expansion of Antarctic Marine Protected Areas’Demonstration of direct ocean carbon capture using hollow fiber membrane contactors
Published 13 June 2023 Science ClosedTags: chemistry, laboratory, methods, mitigation, modeling
The focus of membrane carbon capture to date has been primarily on point source capture, such as power plants and industrial capture. However, membrane technology can also play a role in negative emissions technology, such as direct air capture and direct ocean capture. Direct ocean capture has a few potential advantages over direct air capture, such as avoiding land use and coupling with offshore wind and offshore storage. The use and feasibility of hollow fiber membrane contactors (HFMCs) for direct ocean carbon capture with benign aqueous basic carbon dioxide solvents is assessed here through a multifaceted approach. A 1D HFMC model incorporates fluid dynamics and the chemical kinetics of both ocean water and aqueous sodium hydroxide solvent in order to simulate CO2 flux behavior in two flow configurations. Lab scale experiments of this system then guide a model refinement and validation process until experimental behaviors are predicted through computation. A preliminary technoeconomic assessment then uses computational and experimental results to estimate the carbon capture cost when the system is scaled to remove 0.98 Mtonnes CO2/year. Computational results suggest that higher seawater flow rates and temperatures relative to the sodium hydroxide solvent improve CO2 flux. The technoeconomic assessment suggests that HFMCs may only be cost-competitive if seawater pH is decreased at the membrane interface, thereby increasing the local concentration of dissolved carbon dioxide. These findings indicate that local pH swing on the seawater side will be necessary to feasibly remove carbon dioxide from seawater using HFMCs.
Continue reading ‘Demonstration of direct ocean carbon capture using hollow fiber membrane contactors’Seawater alkalinity enhancement with magnesium hydroxide and its implication for carbon dioxide removal
Published 13 June 2023 Science ClosedTags: chemistry, laboratory, methods, mitigation
For the first time we used lab and wind-wave tank experiments to prove the concept of using Mg(OH)2 for the ocean alkalinity enhancement and carbon dioxide removal approach (OAE-CDR). Experiment results showed up to 370 μmol kg−1 seawater total alkalinity (TA) increase without precipitation, stable enhanced TA, and OAE-CDR efficiency (ΔDIC/ΔTA) consistent with theoretical calculation. Based on the experimental results, we calculated the global Mg(OH)2 OAE-CDR efficiency and CO2 sink from this approach. The efficiency is in favor of lower initial DIC to TA ratio, lower temperature, and higher atmospheric CO2, and therefore is the lowest at the equator (0.7–0.8) and increases with latitude (1.0–1.2 above 70 N/S). However, factoring in the ocean’s surface area, low latitude regions can absorb more atmospheric CO2. We conservatively estimate that 44. 4 × 109 ton of CO2 (~ 3.3 times of current annual CO2 sink in the ocean) could be removed from the atmosphere with 175 μmol kg−1 Mg(OH)2 (equivalent to 350 μmol kg−1 of TA) added to the top 10 m of the ocean.
Continue reading ‘Seawater alkalinity enhancement with magnesium hydroxide and its implication for carbon dioxide removal’Ocean afforestation’s effect on deep-sea biogeochemistry
Published 8 June 2023 Science ClosedTags: biogeochemistry, chemistry, individualmodeling, mitigation, modeling
If climate change is left unchecked it will lead to unprecedented deterioration of human health, economy and ecology. According to the IPCC, in order to avoid severe consequences, global warming will need to be limited to 1.5°C. However, the 1.5°C warming will be exceeded if current trends continue, which is why the need for Carbon Dioxide Removal (CDR) has become increasingly apparent. Ocean afforestation is currently one of the most promising CDR approaches, with the least competition for space, high carbon sequestration potential and high technical feasibility. Ocean afforestation approaches attempt to sequester carbon by sinking seaweed to deep-sea areas. This research looks at the consequences of the seaweed input to deep-seafloor. An early diagenetic model called RADI is used to predict the fate of the carbon and the effect on biogeochemistry. The model was adapted to include new sources of sedimentary organic matter, such as seaweed (Sargassum, Saccharina, Macrocystis) and Sugarcane bagasse, which are currently considered potential candidates for ocean afforestation purposes. Sargassum, an invasive free-floating species, has a large sequestration potential and is readily available. Sinking Sargassum in pulse, large amounts over short times, leads to high carbon retention in the sediment (up to 25% after two years) but leads to hypoxic conditions in the sediment for at least two years after addition. Continuous Sargassum sinking also leads to carbon sequestration but with a much less invasive impact on the seafloor. The carbon from continuous sinking does not remain in the sediment but is remineralized and flows out to the bottom water as inorganic carbon. Saccharina, an edible coastal species, could be used to grow on free floating organic buoy. Having the additional sequestration benefit from the carbon fixed in the organics. Carbon retention is highest for the pulse addition of this seaweed (33% after two years), compared to a continuous approach (30%) in which the seaweed is added over longer timescales in small amounts. Since this pulse input also leads to hypoxic conditions in the sediment, the continuous approach is more favourable for this approach. Macrocystis, the giant kelp known for forming ecosystems, is a fast-growing coastal species. This species requires harvesting and baling for use in carbon sequestration. Carbon retention is much higher for pulse addition (30%). Sugar cane bagasse is an agricultural residue with high carbon content. Sinking this residue to anoxic basins, has been proven to retain more carbon than in oxygenated bottom waters. This can be confirmed with the results which showed a carbon retention of up to 50% after two years. The effect on the benthic biome is also less intense since the low oxygen conditions already necessitate a specialized microbiome. Sugarcane bagasse is furthermore the only addition capable of increasing bottom water pH. Whereas all seaweed approaches had higher dissolved inorganic carbon than alkalinity flow to the bottom water, resulting in net acidification. This research provides a first look into the effects of ocean afforestation on deep sea biogeochemistry, and illustrates the importance of the composition, quantity and input duration of the seaweed used.
Continue reading ‘Ocean afforestation’s effect on deep-sea biogeochemistry’Ocean alkalinity enhancement through restoration of blue carbon ecosystems
Published 1 June 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, mitigation, modeling
Blue carbon ecosystems provide a wide range of ecosystem services, are critical for maintaining marine biodiversity and may potentially serve as sites of economically viable carbon dioxide removal through enhanced organic carbon storage. Here we use biogeochemical simulations to show that restoration of these marine ecosystems can also lead to permanent carbon dioxide removal by driving ocean alkalinity enhancement and atmosphere-to-ocean CO2 fluxes. Most notably, our findings suggest that restoring mangroves, which are common in tropical shallow marine settings, will lead to notable local ocean alkalinity enhancement across a wide range of scenarios. Enhanced alkalinity production is linked to increased rates of anaerobic respiration and to increased dissolution of calcium carbonate within sediments. This work provides further motivation to pursue feasible blue carbon restoration projects and a basis for incorporating inorganic carbon removal in regulatory and economic incentivization of blue carbon ecosystem restoration.
Continue reading ‘Ocean alkalinity enhancement through restoration of blue carbon ecosystems’Carbon dioxide mineralization by electrode separation for quick carbon reduction and sequestration in acidified seawater
Published 22 May 2023 Science ClosedTags: chemistry, laboratory, methods, mitigation, North Pacific
Aiming to sequestrate the excessive carbon dioxide and convert the acidified seawater, an improved method of carbon dioxide mineralization is developed based on electrode separation mechanism and extra oxygen-supplying technique. By electrode separation the neutralizations of the anodic acidity and the cathodic alkalinity, as well as the precipitation and the dissolution of calcium carbonate (CaCO3), are prevented. In addition, the extra-supplied oxygen prevents the evolution of hydrogen, which enhances the electric conductivity of the porous cathode and the deposition of CaCO3. A series of indoor physical experiments were conducted and the results show that the acidified seawater was successfully converted to alkaline in 72h. The speed of carbon mineralizing sequestration is significantly enhanced by supplying extra oxygen. The carbon dioxide mineralization speed increases with the immerse ratio of the aerator due to the more reacted oxygen and the less hydrogen evolution, which gives more porous space in the cathode for more conductive seawater and more deposition of CaCO3. The extra-supplied oxygen increases the CaCO3 -deposition by 100-214% under excessive atmospheric- CO2 conditions and 117-200% under normal atmospheric- CO2 conditions, respectively. This method has an application potential for quick conversion of locally acidified seawater in emergent circumstances.
Continue reading ‘Carbon dioxide mineralization by electrode separation for quick carbon reduction and sequestration in acidified seawater’Potential role of seaweeds in climate change mitigation
Published 11 May 2023 Science ClosedTags: biogeochemistry, mitigation, review
Highlights
- Seaweed carbon accounting is yet to be fully constrained.
- Seaweed products have the potential to lower industrial emissions.
- Seaweed farms sequester carbon at site but at a limited scale to date.
- Quantifying carbon seqestration from wild seaweed restoration remains ellusive.
- Sinking seaweed has scalability but carries many risks and uncertainties.
Abstract
Seaweed (macroalgae) has attracted attention globally given its potential for climate change mitigation. A topical and contentious question is: Can seaweeds’ contribution to climate change mitigation be enhanced at globally meaningful scales? Here, we provide an overview of the pressing research needs surrounding the potential role of seaweed in climate change mitigation and current scientific consensus via eight key research challenges. There are four categories where seaweed has been suggested to be used for climate change mitigation: 1) protecting and restoring wild seaweed forests with potential climate change mitigation co-benefits; 2) expanding sustainable nearshore seaweed aquaculture with potential climate change mitigation co-benefits; 3) offsetting industrial CO2 emissions using seaweed products for emission abatement; and 4) sinking seaweed into the deep sea to sequester CO2. Uncertainties remain about quantification of the net impact of carbon export from seaweed restoration and seaweed farming sites on atmospheric CO2. Evidence suggests that nearshore seaweed farming contributes to carbon storage in sediments below farm sites, but how scalable is this process? Products from seaweed aquaculture, such as the livestock methane-reducing seaweed Asparagopsis or low carbon food resources show promise for climate change mitigation, yet the carbon footprint and emission abatement potential remains unquantified for most seaweed products. Similarly, purposely cultivating then sinking seaweed biomass in the open ocean raises ecological concerns and the climate change mitigation potential of this concept is poorly constrained. Improving the tracing of seaweed carbon export to ocean sinks is a critical step in seaweed carbon accounting. Despite carbon accounting uncertainties, seaweed provides many other ecosystem services that justify conservation and restoration and the uptake of seaweed aquaculture will contribute to the United Nations Sustainable Development Goals. However, we caution that verified seaweed carbon accounting and associated sustainability thresholds are needed before large-scale investment into climate change mitigation from seaweed projects.
Continue reading ‘Potential role of seaweeds in climate change mitigation’Response of ocean acidification to atmospheric carbon dioxide removal
Published 9 May 2023 Science ClosedTags: chemistry, globalmodeling, mitigation, modeling
Artificial CO2 removal from the atmosphere (also referred to as negative CO2 emissions) has been proposed as a potential means to counteract anthropogenic climate change. Here we use an Earth system model to examine the response of ocean acidification to idealized atmospheric CO2 removal scenarios. In our simulations, atmospheric CO2 is assumed to increase at a rate of 1% per year to four times its pre-industrial value and then decreases to the pre-industrial level at a rate of 0.5%, 1%, 2% per year, respectively. Our results show that the annual mean state of surface ocean carbonate chemistry fields including hydrogen ion concentration ([H+]), pH and aragonite saturation state respond quickly to removal of atmospheric CO2. However, the change of seasonal cycle in carbonate chemistry lags behind the decline in atmospheric CO2. When CO2 returns to the pre-industrial level, over some parts of the ocean, relative to the pre-industrial state, the seasonal amplitude of carbonate chemistry fields is substantially larger. Simulation results also show that changes in deep ocean carbonate chemistry substantially lag behind atmospheric CO2 change. When CO2 returns to its pre-industrial value, the whole-ocean acidity measured by [H+] is 15%-18% larger than the pre-industrial level, depending on the rate of CO2 decrease. Our study demonstrates that even if atmospheric CO2 can be lowered in the future as a result of net negative CO2 emissions, the recovery of some aspects of ocean acidification would take decades to centuries, which would have important implications for the resilience of marine ecosystems.
Continue reading ‘Response of ocean acidification to atmospheric carbon dioxide removal’Ocean acidification and the Anthropocene: an emergency response
Published 5 May 2023 Science ClosedTags: mitigation, policy
This chapter considers the threat of ocean acidification from the perspective of both harm to ocean ecological systems and positive climate feedbacks. A survey of current governance responses demonstrates an alarming failure. No international governance regime currently accounts for ocean acidification by requiring significant and additional reductions in CO2 emissions. In an oceans context, acidification is treated as a gradual background stressor along with a range of climate change impacts. Against this backdrop and employing the Anthropocene concept, together with emerging realization that we face a planetary emergency, this chapter proposes a radical change of approach. It proposes that we begin with emergency closure of a large swath of the ocean – namely areas beyond national jurisdiction. While not an end in itself, emergency closure of the Earth’s largest ecological system is a critical place to begin confronting what the Anthropocene means, the implications for all life, and how humanity must govern itself. Change here may seed a very different understanding of what is required as we confront the reality of an Earth system as a global ecological commons on the verge of abrupt, irreversible, and destructive changes. At the very least, such an emergency response may (not will) slow the rate of accumulating harm while we formulate entirely new human responses fully commensurate with the complex and urgent existential crisis of our making.
Continue reading ‘Ocean acidification and the Anthropocene: an emergency response’
