Posts Tagged 'mitigation'

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Short-term impact assessment of ocean liming: a copepod exposure test

Published 19 December 2023 Science Closed
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Highlights

  • Ocean liming (OL) may cause temporary pH peaks which can be dangerous for marine life.
  • Short-term exposure tests (<24 h) are required to evaluate the impact of OL.
  • At pH 9 for exposures lower than 6 h, copepods showed no adverse effects.
  • At pH ≥ 10, adverse effects on copepods were seen for exposures shorter than 3 h.

Abstract

Ocean liming (OL) is a potential carbon dioxide removal (CDR) method that aims to increase the ocean’s capacity to absorb atmospheric CO2 by adding hydrated lime to the surface ocean. Modeling studies indicate that OL may cause temporary pH spikes lasting several minutes, depending on the lime sparging rate. Little is known about the short-term effects of these spikes on marine organisms. Aim of the present study is to investigate these effects on the copepod Acartia tonsa. Copepods were exposed to different pH conditions (9, 10, 11, 12) by dosing different hydrated lime solutions. Copepod mortality, movements, and behavior were recorded. At pH 9 for short exposure times (<6 h), no negative effects were observed indicating a potential tolerable threshold for OL applications. At longer exposure times (>6 h) and pH higher than 9, negative effects (mortality and sublethal effects) were found significantly higher than in the control.

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Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements, and calculations

Published 11 December 2023 Science Closed
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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 stabilise 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. Key findings are that (1) theoretical CO2 uptake potential (global mean of 0.84 mol of CO2 per mole of TA added) based on carbonate chemistry calculations is probably secondary in determining the oceanic region in which OAE would be best; (2) carbonate chemistry sampling is recommended to involve gentle pressure filtration to remove calcium carbonate (CaCO3) that might have been precipitated upon TA increase as it would otherwise interfere with a number of analyses; (3) samples for DIC and TA can be stabilised to avoid the risk of secondary CaCO3 precipitation during sample storage; and (4) some OAE feedstocks require additional adjustments to carbonate chemistry speciation calculations using available programs and routines, for instance if seawater magnesium or calcium concentrations are modified.

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Monitoring, reporting, and verification for ocean alkalinity enhancement

Published 11 December 2023 Science Closed
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Monitoring, reporting, and verification (MRV) refers to the multistep process of monitoring the amount of greenhouse gas removed by a carbon dioxide removal (CDR) activity and reporting the results of the monitoring to a third party. The third party then verifies the reporting of the results. While MRV is usually conducted in pursuit of certification in a voluntary or regulated CDR market, this chapter focuses on key recommendations for MRV relevant to ocean alkalinity enhancement (OAE) research. Early stage MRV for OAE research may become the foundation on which markets are built. Therefore, such research carries a special obligation toward comprehensiveness, reproducibility, and transparency. Observational approaches during field trials should aim to quantify the delivery of alkalinity to seawater and monitor for secondary precipitation, biotic calcification, and other ecosystem changes that can feed back on sources or sinks of greenhouse gases where alkalinity is measurably elevated. Observations of resultant shifts in the partial pressure of CO2 (pCO2) and ocean pH can help determine the efficacy of OAE and are amenable to autonomous monitoring. However, because the ocean is turbulent and energetic and CO2 equilibration between the ocean and atmosphere can take several months or longer, added alkalinity will be diluted to perturbation levels undetectable above background variability on timescales relevant for MRV. Therefore, comprehensive quantification of carbon removal via OAE will be impossible through observational methods alone, and numerical simulations will be required. The development of fit-for-purpose models, carefully validated against observational data, will be a critical part of MRV for OAE.

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Seaweed farming environments do not always function as CO2 sink under synergistic influence of macroalgae and microorganisms

Published 6 December 2023 Science Closed
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Seaweed farming contributes substantial amounts of organic carbon to the ocean, part of which can be locked for a long term in the ocean and perform the function of ocean carbon sequestration, and the other part can be converted into inorganic carbon through microbial mineralization and aerobic respiration, affecting the pCO2, pHT and dissolved oxygen of seawater. It is generally believed that seaweed farming will cause the seawater to become a sink of CO2 due to carbon fixation by macroalgal photosynthesis. However, little attention has been paid to the fact that seaweed farming environment may sometimes become a source rather than a sink of CO2. Here, through in-situ mesocosm cultivation experiments and eight field investigations covering different kelp growth stages in an intensive farming area in China, we found that compared with the surrounding seawater without kelps, the seawater at the fast-growth stage of kelp was a sink of CO2 (pCO2 decreased by 17−73 μatm), but became a source of CO2 at the aging stage of kelp (pCO2 increased by 20−37 μatm). Concurrently, seawater pHT experienced a transition from increase (by 0.02−0.08) to decline (by 0.03−0.04). In-situ mesocosm cultivation experiments showed that the positive environmental effects (i.e., pCO2 decrease and pHT increase) induced by kelps at the early growth stage could be offset within only 3 days at the late-growth and aging stages. The release of dissolved organic carbon by kelps at the late growth stage increased significantly, supporting the enhancement in microbial abundance and respiration, which was manifested by the remarkable decrease in seawater dissolved oxygen, ultimately leading to CO2 release exceeding photosynthetic CO2 absorption. This study suggests that mature farmed kelps should be harvested in time to best utilize their carbon sink function and environmental benefits, which has guiding significance for the rational management of seaweed farming.

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Assessing the technical aspects of ocean-alkalinity-enhancement approaches

Published 5 December 2023 Science Closed
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Ocean alkalinity enhancement (OAE) is an emerging strategy that aims to mitigate climate change by increasing the alkalinity of seawater. This approach involves increasing the alkalinity of the ocean to enhance its capacity to absorb and store carbon dioxide (CO2) from the atmosphere. This chapter presents an overview of the technical aspects associated with the full range of OAE methods being pursued and discusses implications for undertaking research on these approaches. Various methods have been developed to implement OAE, including the direct injection of alkaline liquid into the surface ocean; dispersal of alkaline particles from ships, platforms, or pipes; the addition of minerals to coastal environments; and the electrochemical removal of acid from seawater. Each method has its advantages and challenges, such as scalability, cost effectiveness, and potential environmental impacts. The choice of technique may depend on factors such as regional oceanographic conditions, alkalinity source availability, and engineering feasibility. This chapter considers electrochemical methods, the accelerated weathering of limestone, ocean liming, the creation of hydrated carbonates, and the addition of minerals to coastal environments. In each case, the technical aspects of the technologies are considered, and implications for best-practice research are drawn. The environmental and social impacts of OAE will likely depend on the specific technology and the local context in which it is deployed. Therefore, it is essential that the technical feasibility of OAE is undertaken in parallel with, and informed by, wider impact assessments. While OAE shows promise as a potential climate change mitigation strategy, it is essential to acknowledge its limitations and uncertainties. Further research and development are needed to understand the long-term effects, optimize techniques, and address potential unintended consequences. OAE should be viewed as complementary to extensive emission reductions, and its feasibility may be improved if it is operated using energy and supply chains with minimal CO2 emissions.

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General considerations for experimental research on ocean alkalinity enhancement

Published 4 December 2023 Science Closed
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Ocean alkalinity enhancement (OAE) is proposed as an approach to capture carbon by adding alkaline substances to seawater to enhance the ocean’s natural carbon sink. These substances include minerals, such as olivine, or artificial substances, such as lime or some industrial byproducts. Deployment of OAE will lead to complex and dynamic changes in the seawater carbonate chemistry, and in some cases the addition of other compounds and impurities from the minerals. While OAE alters the carbonate chemistry in a very different way, much can be learned from the abundant literature on ocean acidification documenting the impact of changes in the carbonate chemistry on marine life from genes to ecosystems. A vast majority of the experimental work was performed by manipulating the concentration of carbon dioxide in seawater under constant alkalinity (TA) to simulate near-future ocean acidification. Understanding the impact of changes in alkalinity on marine species and the ecosystem is less understood. In the context of OAE, it is critical to resolve such impacts, alone or in combination with other compounds and impurities from the minerals to be co-released during implementation, to ensure that any field manipulation does not translate into damaging biological effects. As for other environmental drivers, this will require an understanding across all the levels of biological organizations from species to ecosystems over relevant time exposure considering the method of deployment (e.g., dilution, repeated exposure) and factors such as local adaptation. Such complex questions cannot be resolved using a single approach, and a combination of monitoring, modeling, laboratory, natural (i.e., proxies or analogs), and field experiments will be required. This chapter summarizes some key general considerations for experimental design. It also compares strengths and weaknesses of the different approaches. We will also consider best practices relevant to OAE such as the need to properly monitor and consider the addition of trace elements and byproducts, as well as potential interactions with other naturally occurring drivers.

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Dive industry perspectives on threats to coral reefs: a comparative study across four Asia-Pacific countries

Published 15 November 2023 Science Closed
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The combined effects of climate change, marine tourism and other stressors threaten the ecological and economic sustainability of coral reefs. This study investigates dive industry stakeholder awareness of the threats to coral reefs through structured interviews with Dive Masters, company managers and marine management agencies in Vietnam, Australia, Malaysia and Indonesia. Stakeholders from all locations have observed degradation of local reefs. Destructive fishing was identified as the principal threat in all regions except Australia. Most participants identified threats from climate change and marine tourism. There was a lack of awareness about ocean acidification by all participants from Maluku, Indonesia. However, ocean acidification could make coral more fragile and, therefore, vulnerable to diver-induced damage. The majority of Dive Masters across all regions provide pre-dive briefings to reduce diver impacts and participate in environmental activities to protect local reefs. Stakeholders in three regions thought there was capacity to expand the local dive industry. However, in Nha Trang Vietnam, most industry stakeholders thought they were at, or exceeded, carrying capacity, whereas marine management employees thought there was room to expand. This study highlights an opportunity to improve diver education on the vulnerability of coral to damage in acidifying oceans. This study also identifies various non-regulatory and regulatory strategies used to reduce diver impacts, emphasising the value of multi-national knowledge sharing between the dive industry and regulatory agencies for adaptive management.

HIGHLIGHTS

  • Dive industry stakeholders are concerned about threats to coral reefs.
  • Impacts from diving activities were recognised in three of four regions.
  • There was great discrepancy between regions in the awareness of ocean acidification.
  • Most dive industry stakeholders are engaged in marine conservation activities.
  • Some marine managers and industry stakeholders had discrepant views on diver carrying capacity
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Assessing the role of natural kelp forests in modifying seawater chemistry

Published 26 October 2023 Science Closed
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Climate change is causing widespread impacts on seawater pH through ocean acidification (OA). Kelp forests, in some locations can buffer the effects of OA through photosynthesis. However, the factors influencing this variation remain poorly understood. To address this gap, we conducted a literature review and field deployments of pH and dissolved oxygen (DO) loggers within four habitats: intact kelp forest, moderate kelp cover, sparse kelp cover and barrens at one site in Port Phillip Bay, a wind-wave dominated coastal embayment in Victoria, Australia. Additionally, a wave logger was placed directly in front of the intact kelp forest and barrens habitats. Most studies reported that kelp increased seawater pH and DO during the day, compared to controls without kelp. This effect was more pronounced in densely populated forests, particularly in shallow, sheltered conditions. Our field study was broadly consistent with these observations, with intact kelp habitat having higher seawater pH than habitats with less kelp or barrens and higher seawater DO compared to barrens, particularly in the afternoon and during calmer wave conditions. Although kelp forests can provide local refuges to biota from OA, the benefits are variable through time and may be reduced by declines in kelp density and increased wave exposure.

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pCO2 decrement through alkalinity enhancement and biological production in a shallow-water ecosystem constructed using steelmaking slag

Published 25 October 2023 Science Closed
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Ocean-based carbon dioxide removal has gained immense attention as a countermeasure against climate change. The enhancement of ocean alkalinity and the creation of new blue carbon ecosystems are considered effective approaches for this. To evaluate the function of steelmaking slag from the viewpoints of CO2 reduction and creation of new blue carbon ecosystems, we conducted a comparative experiment using two mesocosms that replicated tidal-flats and shallow-water ecosystems. Initially, approximately 20 seagrasses (Zostera marina) were transplanted into the shallow-water area in the mesocosm tanks. The use of steelmaking slag is expected to increase the pH by releasing calcium and mitigate turbidity by solidifying dredged soil. In the experimental tank, where dredged soil and steelmaking slag were utilized as bed materials, the pH remained higher throughout the experimental period compared with the control tank, which utilized only dredged soil. As a result, pCO2 remained consistently lower in the experimental tank due to mainly its alkaline effect (March 2019: −10 ± 6 μatm, September 2019: −130 ± 47 μatm). The light environment in the control tank deteriorated due to high turbidity, whereas the turbidity in the experimental tank remained low throughout the year. The number of seagrass shoots in the experimental tank was consistently approximately 20, which was higher than that in the control tank. Additionally, more seaweed and benthic algae were observed in the experimental tank, indicating that it was more conducive to the growth of primary producers. In conclusion, tidal-flat and shallow-water ecosystems constructed using dredged soil and steelmaking slag are expected to enhance CO2 uptake and provide a habitat for primary producers that is superior to those constructed using dredged soil only.

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Assessing the impact of CO2 equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Published 25 October 2023 Science Closed
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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.

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Oyster reefs’ control of carbonate chemistry—Implications for oyster reef restoration in estuaries subject to coastal ocean acidification

Published 12 October 2023 Science Closed
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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.

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Investigating the effect of silicate and calcium based ocean alkalinity enhancement on diatom silicification

Published 29 September 2023 Science Closed
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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.

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Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments

Published 19 September 2023 Science Closed
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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.

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Ocean acidification in the Philippines and the potential role of water pollution management in mitigating an unaddressed threat

Published 10 August 2023 Science Closed
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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.

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Laboratory experiments in ocean alkalinity enhancement research

Published 20 July 2023 Science Closed
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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.

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The potential role of Posidonia oceanica for mitigating acidification on coastal waters of Europe

Published 12 July 2023 Science Closed
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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.

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Mesocosm experiments in ocean alkalinity enhancement research

Published 12 July 2023 Science Closed
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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.

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Seawater carbonate system considerations for ocean alkalinity enhancement research

Published 12 July 2023 Science Closed
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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.

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Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?

Published 20 June 2023 Science Closed
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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.

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Broaden research on ocean alkalinity enhancement to better characterize social impacts

Published 15 June 2023 Science Closed
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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.

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