Over the past 250 years, atmospheric carbon dioxide concentrations have risen steadily from 277 ppm to 405 ppm, leading to the exacerbation of the effects of climate change. As a result, new technologies are being developed to remove carbon from the atmosphere, such as negative emission technologies (NETs). One proposed NET is Ocean Alkalinity Enhancement (OAE), which would mimic the ocean’s natural weathering processes and sequester carbon dioxide from the atmosphere. An analysis of published data investigating the effects of elevated pH on phytoplankton growth rate and experimental assessment of pH dependence of viability and growth rate was used to assess the potential impacts of OAE. Viability was assessed with a modified Serial Dilution Culture – Most Probable Number assay. Chlorophyll a fluorescence was used to test for changes in growth rates and photosynthetic competence. The results from this study suggest that there will be no significant impact on the viability or growth rates of Thalassiosira pseudonana or Pavlova lutheri with short-term (10 minute) exposure to elevated pH. However, when long-term (days) exposure occurs there is a significant decrease in growth rates with elevated pH. Short-term exposure is anticipated to more closely mirror the natural systems in which OAE will be implemented because of system flushing and replenishment of nutrients. These preliminary findings suggest that there will be little to no impact on a variety of taxonomic groups of phytoplankton when OAE occurs in naturally flushed systems.
Continue reading ‘Assessing the impacts of simulated ocean alkalinity enhancement on viability and growth of cultures of near-shore species of phytoplankton’Posts Tagged 'mitigation'
Assessing the impacts of simulated ocean alkalinity enhancement on viability and growth of cultures of near-shore species of phytoplankton
Published 27 April 2023 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, growth, laboratory, mitigation, modeling, North Atlantic, otherprocess, photosynthesis, phytoplankton
Adaptive governance of coral reefs: cases of Florida and the Caribbean
Published 25 April 2023 Science ClosedTags: biological response, BRcommunity, corals, mitigation, policy
Coral reefs are one of the most imperiled yet one of the most valuable ecosystems on the planet, providing food, medicine, and property protection to hundreds of millions of coastal people all over the world. Coral reefs are being lost at an unprecedented rate throughout their range. In the Florida Reef Tract alone, 98% of hard coral has died due to heat waves, disease, and poor water quality, making modern reefs almost unrecognizable. Given the stress that coral reefs are facing due to human and natural causes, there are two key knowledge gaps that are essential to address: the significance of the losses of culturally important benefits that coral reefs provide to people, and the ways that people are adapting to the rapid loss of coral reefs. This dissertation aims to address both gaps.
Continue reading ‘Adaptive governance of coral reefs: cases of Florida and the Caribbean’Ocean acidification as a governance challenge in the Mediterranean Sea: impacts from aquaculture and fisheries
Published 25 April 2023 Science ClosedTags: chemistry, field, fisheries, Mediterranean, mitigation, modeling, policy, regionalmodeling, review
Despite the progress in the international and regional governance efforts at the level of climate change, ocean acidification (OA) remains a global problem with profoundly negative environmental, social, and economical consequences. This requires extensive mitigation and adaptation effective strategies that are hindered by current shortcomings of governance. This multidisciplinary chapter investigates the risks of ocean acidification (OA) for aquaculture and fisheries in the Mediterranean Sea and its sub-basins and the role of regional adaptive governance to tackle the problem. The identified risks are based on the biological sensitivities of the most important aquaculture species and biogenic habitats and their exposure to the current and future predicted (2100) RCP 8.5 conditions. To link OA exposure and biological sensitivity, we produced spatially resolved and depth-related pH and aragonite saturation state exposure maps and overlaid these with the existing aquaculture industry in the coastal waters of the Mediterranean basin to demonstrate potential risk for the aquaculture in the future. We also identified fisheries’ vulnerability through the indirect effects of OA on highly sensitive biogenic habitats that serve as nursery and spawning areas, showing that some of the biogenic habitats are already affected locally under existing OA conditions and will be more severely impacted across the entire Mediterranean basin under 2100 scenarios. This provided a regional vulnerability assessment of OA hotspots, risks and gaps that created the baseline for discussing the importance of adaptive governance and recommendations for future OA mitigation/adaptation strategies. By understanding the risks under future OA scenarios and reinforcing the adaptability of the governance system at the science-policy interface, best informed, “situated” management response capability can be optimised to sustain ecosystem services.
Continue reading ‘Ocean acidification as a governance challenge in the Mediterranean Sea: impacts from aquaculture and fisheries’Aquaculture mapping in the context of climate change
Published 24 April 2023 Science ClosedTags: fisheries, mitigation, North Pacific, policy, socio-economy
The development of aquaculture is facing unprecedented pressures from climate change, resource constraints, environmental pollution, energy consumption, and other factors. For coping with these challenges and for ensuring sustainable development of aquaculture, spatial planning in aquaculture activities become more and more important. An ecosystem-based approach for aquaculture mapping is needed to strategically and comprehensively balance the location, aquaculture type, and stakeholders’ interests. In this chapter, we aim to describe the definition, key steps, and methods of aquaculture zoning, especially in the context of climate change (e.g., global warming, ocean acidification, hypoxia/anoxia, sea level rising, and extreme events). We also provide two case studies of aquaculture mapping in China.
Continue reading ‘Aquaculture mapping in the context of climate change’What conservation strategies support the adaptive capacity of coastal ecosystems in three island states facing a changing climate in Micronesia?
Published 20 April 2023 Science ClosedTags: biological response, BRcommunity, corals, mitigation, review, socio-economy, South Pacific
Coastal ecosystems, such as coral reefs, mangroves, and seagrass beds, are highly vulnerable to the impacts of climate change. The degradation and loss of these ecosystems, stemming from the increased impacts of climate change-related drivers, threaten the well-being of island communities in Micronesia, as they are very reliant on and connected with these coastal ecosystems. Supporting the adaptive capacity of ecosystems through climate adaptive conservation, and thus better equipping them to recover from and adapt to the potential impacts, in turn reduces the vulnerability of the social-ecological system. This thesis identified five main climate change-related drivers that impact coastal systems across three selected states in Micronesia. First, based on a conceptual social-ecological systems (SES) framework, a literature review and analysis were conducted to identify and select three ecosystem adaptive capacity (AC) elements: Heterogeneity, connectivity, and ecosystem functioning. Building on that, second, a literature review aided the identification of climate adaptive conservation strategies and related actions that can support the adaptive capacity of ecosystems. Following a qualitative content analysis, eight climate adaptive conservation strategies and 26 activities were selected and categorized. Third, the extent of (1) the strategy effectiveness, (2) their integration in conservation policy and planning documents, and (3) their implementation on a national scale were evaluated through a semi-quantitative expert consultation in each of the selected states, exemplified with coral reefs.
The findings from this research showed that while the climate adaptive strategies and activities were considered effective in supporting the adaptive capacity of coral reefs in Micronesia, the extent of their implementation ranked low. Strategies, such as “Addressing non-climatic drivers” were considered highly effective, however their implementation fell comparably short. Contrary, targeting heterogeneity was considered of least importance. Thus, as their regional implementation ranked low, the ability of the strategies to support coral adaptive capacity was limited for all three countries. Particularly, the upscaling and mainstreaming of these strategies was considered crucial by the experts. Therefore, this research proposed to prioritize addressing non-climatic drivers, supporting coral reef restoration, and recommended to integrate communities in the design of climate adaptive conservation. Further to apply actionable co-produced science to advance the evidence base and applicability of the strategies in supporting ecosystem AC.
Continue reading ‘What conservation strategies support the adaptive capacity of coastal ecosystems in three island states facing a changing climate in Micronesia?’Resilience of a giant clam subsistence fishery in Kiribati to climate change
Published 20 April 2023 Science ClosedTags: fisheries, mitigation, North Pacific, policy, socio-economy
Changes in sea surface temperature have historically impacted the habitat of giant clams in Kiribati. In many islands of Kiribati, the four species of giant clam have largely withstood these environmental changes, through adaptive responses to anthropogenic pressures. The Kiribati giant clam fishery is a data-limited multi-species fishery, so in adopting and applying a comprehensive resilience framework to highlight attributes conferring and limiting resilience across the ecological, governance, and socio-economic aspects of the fishery we used knowledge co-production and the precautionary principle approach to better inform place-based attempts to operationalise resilience measures. We found that the resilience of the fishery to marine heatwaves and ocean acidification, as highlighted by local stakeholders, will depend on the ability of fisheries stakeholders to act collectively, with flexibility, to implement adaptive governance. Climate change, coupled with human impacts, have reduced ecological resilience in the urbanised island of South Tarawa, in contrast to the more remote or sparsely populated islands. In South Tarawa, governance and social processes are less flexible, leading to declines in the local subsistence clam fishery. Conversely, on several remote outer islands, where the social-ecological system has shown promise in combating these anthropogenic influences (e.g., through adaptive community-based fisheries management), the ecological resilience has improved, and the subsistence clam fishery has persisted. Our case study demonstrates the importance of a participatory approach and local knowledge when assessing climate resilience and identifies pathways of resilience in other small-scale fisheries, especially when data are limited.
Continue reading ‘Resilience of a giant clam subsistence fishery in Kiribati to climate change’A biogeochemical model of mineral-based ocean alkalinity enhancement: impacts on the biological pump and ocean carbon uptake
Published 14 April 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, methods, mitigation, modeling
Minimizing anthropogenic climate disruption in the coming century will likely require carbon dioxide removal (CDR) from Earth’s atmosphere in addition to deep and rapid cuts to greenhouse gas emissions. Ocean alkalinity enhancement — the modification of surface ocean chemistry to drive marine uptake of atmospheric CO2 — is seen as a potentially significant component of ocean-based CDR portfolios. However, there has been limited mechanistic exploration of the large-scale CDR potential of mineral-based ocean alkalinity enhancement, potential bottlenecks in alkalinity release, and the biophysical impacts of alkaline mineral feedstocks on marine ecology and the marine biological carbon pump. Here we a series of biogeochemical models to evaluate the gross CDR potential and environmental impacts of ocean alkalinity enhancement using solid mineral feedstocks. We find that natural alkalinity sources — basalt and olivine — lead to very low CDR efficiency while strongly perturbing marine food quality and fecal pellet production by marine zooplankton. Artificial alkalinity sources — the synthetic metal oxides MgO and CaO — are potentially capable of significant CDR with reduced environmental impact, but their deployment at scale faces major challenges associated with substrate limitation and process CO2 emissions during feedstock production. Taken together, our results highlight distinct challenges for ocean alkalinity enhancement as a CDR strategy and indicate that mineral-based ocean alkalinity enhancement should be pursued with caution.
Continue reading ‘A biogeochemical model of mineral-based ocean alkalinity enhancement: impacts on the biological pump and ocean carbon uptake’Simulated carbon cycle and Earth system response to atmospheric CO2 removal
Published 12 April 2023 Science ClosedTags: chemistry, globalmodeling, mitigation, modeling
To project possible future climate change, it is important to understand Earth system response to CO2 removal, a potential key method to limit global warming. Previous studies examined some aspects of Earth system response to different scenarios of CO2 removal, but lacked a systematic analysis of the carbon cycle and climate system response in a consistent modeling framework. We expanded previous studies by using an Earth system model to examine the response of land and ocean carbon cycle, as well as a set of climate variables to idealized scenarios of atmospheric CO2 removal with different removal rates. In the scenarios considered, atmospheric CO2 increases at a rate of 1% per year to four times of its preindustrial level, and then decreases at a rate of 0.5%, 1%, and 2% per year to the preindustrial level. Simulation results show that a reduction of atmospheric CO2 induces CO2 release from both the ocean and terrestrial biosphere, and to keep atmospheric CO2 at a lower level requires the removal of anthropogenic CO2 not only from the atmosphere, but from the ocean and land carbon reservoirs as well. The response of many variables of the Earth system, including temperature, ocean heat content, sea level, deep ocean acidity, and permafrost area and carbon, lags the decrease in atmospheric CO2 ranging from a few years to many centuries. A few centuries after atmospheric CO2 returns to the preindustrial level, sea level is still substantially higher than the preindustrial level, and permafrost continues losing CO2 to the atmosphere. Our study demonstrates that to offset previous positive CO2 emissions by atmospheric CO2 removal does not mean to offset climate consequence of positive CO2 emissions. Rapid and deep reduction in CO2 emissions is key to prevent and limit increasing risks from further warming. Our study provides new insights into the carbon cycle and climate system response to CO2 removal, which would help to assess future climate change and the associated impacts.
Continue reading ‘Simulated carbon cycle and Earth system response to atmospheric CO2 removal’Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification
Published 11 April 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, mitigation, modeling
Carbon dioxide removal and solar radiation modification (SRM) are two classes of proposed climate intervention methods. A thorough understanding of climate system response to these methods calls for a good understanding of the carbon cycle response. In this study, we used an Earth system model to examine the response of global climate and carbon cycle to artificial ocean alkalinization (AOA), a method of CO2 removal, and reduction in solar irradiance that represents the overall effect of solar radiation modification. In our simulations, AOA is applied uniformly over the global ice-free ocean under the RCP8.5 scenario to bring down atmospheric CO2 to the level of RCP4.5, and SRM is applied uniformly over the globe under the RCP8.5 scenario to bring down global mean surface temperature to the level of RCP4.5. Our simulations show that with the same goal of temperature stabilization, AOA and SRM cause fundamentally different perturbations of the ocean and land carbon cycle. By the end of the 21st century, relative to the simulation of RCP8.5, AOA-induced changes in ocean carbonate chemistry enhances global oceanic CO2 uptake by 983 PgC and increases global mean surface ocean pH by 0.42. Meanwhile, AOA reduces land CO2 uptake by 79 PgC and reduces atmospheric CO2 concentration by 426 × 10−6. By contrast, relative to the simulation of RCP8.5, SRM has a minor effect on the oceanic CO2 uptake and ocean acidification. SRM-induced cooling enhances land CO2 uptake by 140 PgC and reduces atmospheric CO2 concentration by 63 × 10−6. A sudden termination of SRM causes a rate of temperature change that is much larger than that of RCP8.5. A sudden termination of AOA causes a rate of temperature change that is comparable to that of RCP8.5 and a rate of ocean acidification that is much larger than that of RCP8.5.
Continue reading ‘Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification’Are we ready for ocean acidification? A framework for assessing and advancing policy readiness
Published 29 March 2023 Science ClosedTags: education, mitigation, policy
Effective climate policy that addresses carbon dioxide emissions is essential to minimizing and addressing the impacts of ocean acidification (OA). Here we present a framework to assess the readiness of OA policy, using coral reefs as a focal system. Six dimensions encompass comprehensive preparation by ecosystems and societies for the impacts of OA and other anthropogenic hazards: (1) climate protection measures, (2) OA literacy, (3) area-based management, (4) research and development, (5) adaptive capacity of dependent sectors, and (6) policy coherence. We define standardized indicators, identify leading countries, and evaluate the case study of Australia, the country with the largest coral reef system. The framework provides a rubric for a government unit to self- assess strengths and weaknesses in policy preparedness and to prioritize future endeavors.
Continue reading ‘Are we ready for ocean acidification? A framework for assessing and advancing policy readiness’Assessing synergies and trade-offs of diverging Paris-compliant mitigation strategies with long-term SDG objectives
Published 24 March 2023 Science ClosedTags: mitigation, policy
Highlights
- The Paris Agreement and the Sustainable Development Goals (SDGs) are interlinked.
- Mitigation strategies chosen will affect how SDGs interact.
- Technological and nature-based mitigation pathways increase resource consumption.
- Mitigation strategies relying on behavioural changes limit potential SDG trade-offs.
- Anticipating interdependences supports the design of SDG and Paris-compatible policies.
Abstract
The Sustainable Development Goals (SDGs) and the Paris Agreement are the two transformative agendas, which set the benchmarks for nations to address urgent social, economic and environmental challenges. Aside from setting long-term goals, the pathways followed by nations will involve a series of synergies and trade-offs both between and within these agendas. Since it will not be possible to optimise across the 17 SDGs while simultaneously transitioning to low-carbon societies, it will be necessary to implement policies to address the most critical aspects of the agendas and understand the implications for the other dimensions. Here, we rely on a modelling exercise to analyse the long-term implications of a variety of Paris-compliant mitigation strategies suggested in the recent scientific literature on multiple dimensions of the SDG Agenda. The strategies included rely on technological solutions such as renewable energy deployment or carbon capture and storage, nature-based solutions such as afforestation and behavioural changes in the demand side. Results for a selection of energy-environment SDGs suggest that some mitigation pathways could have negative implications on food and water prices, forest cover and increase pressure on water resources depending on the strategy followed, while renewable energy shares, household energy costs, ambient air pollution and yield impacts could be improved simultaneously while reducing greenhouse gas emissions. Overall, results indicate that promoting changes in the demand side could be beneficial to limit potential trade-offs.
Continue reading ‘Assessing synergies and trade-offs of diverging Paris-compliant mitigation strategies with long-term SDG objectives’Ocean acidification as a governance challenge in the Mediterranean Sea: impacts from aquaculture and fisheries
Published 21 March 2023 Science ClosedTags: fisheries, mitigation, policy, review
Despite the progress in the international and regional governance efforts at the level of climate change, ocean acidification (OA) remains a global problem with profoundly negative environmental, social, and economical consequences. This requires extensive mitigation and adaptation effective strategies that are hindered by current shortcomings of governance. This multidisciplinary chapter investigates the risks of ocean acidification (OA) for aquaculture and fisheries in the Mediterranean Sea and its sub-basins and the role of regional adaptive governance to tackle the problem. The identified risks are based on the biological sensitivities of the most important aquaculture species and biogenic habitats and their exposure to the current and future predicted (2100) RCP 8.5 conditions. To link OA exposure and biological sensitivity, we produced spatially resolved and depth-related pH and aragonite saturation state exposure maps and overlaid these with the existing aquaculture industry in the coastal waters of the Mediterranean basin to demonstrate potential risk for the aquaculture in the future. We also identified fisheries’ vulnerability through the indirect effects of OA on highly sensitive biogenic habitats that serve as nursery and spawning areas, showing that some of the biogenic habitats are already affected locally under existing OA conditions and will be more severely impacted across the entire Mediterranean basin under 2100 scenarios. This provided a regional vulnerability assessment of OA hotspots, risks and gaps that created the baseline for discussing the importance of adaptive governance and recommendations for future OA mitigation/adaptation strategies. By understanding the risks under future OA scenarios and reinforcing the adaptability of the governance system at the science-policy interface, best informed, “situated” management response capability can be optimised to sustain ecosystem services.
Continue reading ‘Ocean acidification as a governance challenge in the Mediterranean Sea: impacts from aquaculture and fisheries’Restoration and coral adaptation delay, but do not prevent, climate-driven reef framework erosion of an inshore site in the Florida Keys
Published 9 February 2023 Science ClosedTags: chemistry, dissolution, mitigation, modeling, multiple factors, North Atlantic, regionalmodeling, temperature
For reef framework to persist, calcium carbonate production by corals and other calcifiers needs to outpace loss due to physical, chemical, and biological erosion. This balance is both delicate and dynamic and is currently threatened by the effects of ocean warming and acidification. Although the protection and recovery of ecosystem functions are at the center of most restoration and conservation programs, decision makers are limited by the lack of predictive tools to forecast habitat persistence under different emission scenarios. To address this, we developed a modelling approach, based on carbonate budgets, that ties species-specific responses to site-specific global change using the latest generation of climate models projections (CMIP6). We applied this model to Cheeca Rocks, an outlier in the Florida Keys in terms of high coral cover, and explored the outcomes of restoration targets scheduled in the coming 20 years at this site by the Mission: Iconic Reefs restoration initiative. Additionally, we examined the potential effects of coral thermal adaptation by increasing the bleaching threshold by 0.25, 0.5, 1 and 2˚C. Regardless of coral adaptative capacity or restoration, net carbonate production at Cheeca Rocks declines heavily once the threshold for the onset of annual severe bleaching is reached. The switch from net accretion to net erosion, however, is significantly delayed by mitigation and adaptation. The maintenance of framework accretion until 2100 and beyond is possible under a decreased emission scenario coupled with thermal adaptation above 0.5˚C. Although restoration initiatives increase reef accretion estimates, Cheeca Rocks will only be able to keep pace with future sea-level rise in a world where anthropogenic CO2 emissions are reduced. Present results, however, attest to the potential of restoration interventions combined with increases in coral thermal tolerance to delay the onset of mass bleaching mortalities, possibly in time for a low-carbon economy to be implemented and complementary mitigation measures to become effective.
Continue reading ‘Restoration and coral adaptation delay, but do not prevent, climate-driven reef framework erosion of an inshore site in the Florida Keys’Effect of seagrass cover loss on seawater carbonate chemistry: implications for the potential of seagrass meadows to mitigate ocean acidification
Published 7 February 2023 Science ClosedTags: abundance, algae, biological response, chemistry, laboratory, mesocosms, mitigation, otherprocess
Seagrass meadows are important marine ecosystems for mitigating ocean acidification because of their ability to raise the pH of seawater during the day. This ability may decrease as a result of the loss of these meadows, which is primarily caused by human activities and climate change. Here, we test the effect of seagrass cover loss on seawater carbonate chemistry to understand how the loss of seagrass meadows affects their ability to mitigate ocean acidification. pH, dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), and aragonite saturation state (ΩAr) were measured in experimental tidal pools with varying proportions of seagrass coverage: 0% (mimicking a complete loss of seagrass meadows); 1%–29% (mimicking the greatest loss of seagrass meadows); 30%–59% (mimicking a moderate loss of seagrass meadows); and 60%–100% (mimicking the lowest loss of seagrass meadows). It was found that as seagrass cover decreased, pH and ΩAr levels in seawater decreased proportionally during the day, while pCO2 and DIC increased. Additionally, correlation analysis showed a strong significant positive correlation between the seagrass cover and pH (rs = 0.9096, p < 0.0001) and ΩAr (rs = 0.9031, p < 0.0001), as well as a strong significant negative correlation between the seagrass cover and pCO2 (rs = −0.9068, p < 0.0001) and DIC (rs = −0.8947, p < 0.0001). These results imply that the 7% annual global loss in seagrass meadows may limit seagrass meadows’ ability to raise the pH of their surrounding seawater during the day, reducing their potential to mitigate ocean acidification. The study recommends that management strategies that minimize anthropogenic activities that cause seagrass loss be implemented in order for seagrass meadows to continue mitigating ocean acidification within their ecosystem and nearby ecosystems.
Continue reading ‘Effect of seagrass cover loss on seawater carbonate chemistry: implications for the potential of seagrass meadows to mitigate ocean acidification’Oregon shellfish farmers: perceptions of stressors, adaptive strategies, and policy linkages
Published 3 February 2023 Science ClosedTags: fisheries, mitigation, policy, socio-economy
Highlights
- Interviews were conducted with fifteen (79%) of oyster farmers in Oregon.
- Farmers are most impacted by environmental, economic, and regulatory stressors.
- Shellfish farmers had matching adaptive strategies to address these stressors.
- Flexible aquaculture policies can help support these strategies.
Abstract
In the United States, domestic oyster aquaculture production is insufficient to meet national demand, thus creating a reliance on international oyster imports for consumption. West coast shellfish farmers are threatened by climate change, including ocean acidification as well as socioeconomic challenges such as labor availability. To expand and enhance United States oyster production, and support domestic food security and livelihoods, a better understanding of the limitations that oyster farmers’ experience, and corresponding pathways forward for adaptation is needed. Through semi-structured interviews conducted with commercial Oregon shellfish farmers, we assess the environmental, economic, social and regulatory stressors impacting oyster growing operations, and the corresponding adaptive strategies employed or envisioned by aquaculture farmers. We find farmers are most impacted by environmental stressors (nuisance species that interact with oysters or oyster habitat negatively), followed by regulatory and economic stressors (permitting and regulations and labor availability). Farmers perceived ocean acidification as a risk, but primarily at the oyster larva stage rather than the juvenile or adult grow-out stage. Examples of farmer-identified adaptive strategies included streamlining permitting and regulations, incentivizing employee retention, and having flexibility in culture type to avoid nuisance species and other environmental stressors. An increase in targeted outreach related to aquaculture policies and engagement with industry, scientists, managers, and policy-makers could facilitate policies that support these and other adaptive strategies.
Continue reading ‘Oregon shellfish farmers: perceptions of stressors, adaptive strategies, and policy linkages’Limits and CO2 equilibration of near-coast alkalinity enhancement
Published 18 January 2023 Science ClosedTags: chemistry, globalmodeling, mitigation, modeling
Ocean alkalinity enhancement (OAE) has recently gained attention as a potential method for carbon dioxide removal (CDR) at gigatonne (Gt) scale, with near-coast OAE operations being economically favorable due to proximity to mineral and energy sources. In this paper we study critical questions which determine the scale and viability of OAE. Which coastal locations are able to sustain a large flux of alkalinity at minimal pH and ΩArag (aragonite saturation) changes? What is the interference distance between adjacent OAE projects? How much CO2 is absorbed per unit of alkalinity added? How quickly does the induced CO2 deficiency equilibrate with the atmosphere? Choosing relatively conservative constraints on ΔpH or ΔOmega, we examine the limits of OAE using the ECCO LLC270 (0.3∘) global circulation model. We find that the sustainable OAE rate varies over 1–2 orders of magnitude between different coasts and exhibits complex patterns and non-local dependencies which vary from region to region. In general, OAE in areas of strong coastal currents enables the largest fluxes and depending on the direction of these currents, neighboring OAE sites can exhibit dependencies as far as 400 km or more. At these steady state fluxes most regional stretches of coastline are able to accommodate on the order of 10s to 100s of megatonnes of negative emissions within 300 km of the coast. We conclude that near-coastal OAE has the potential to scale globally to several Gt CO2 yr−1 of drawdown with conservative pH constraints, if the effort is spread over the majority of available coastlines. Depending on the location, we find a diverse set of equilibration kinetics, determined by the interplay of gas exchange and surface residence time. Most locations reach an uptake efficiency plateau of 0.6–0.8 mol CO2 per mol of alkalinity after 3–4 years, after which there is only slow additional CO2 uptake. Regions of significant downwelling (e.g., around Iceland) should be avoided by OAE deployments, as in such locations up to half of the CDR potential of OAE can be lost to bottom waters. The most ideal locations, reaching a molar uptake ratio of around 0.8, include North Madagascar, California, Brazil, Peru and locations close to the Southern Ocean such as Tasmania, Kerguelen and Patagonia, where the gas exchange appears to occur faster than the surface residence time. However, some locations (e.g., Hawaii) take significantly longer to equilibrate (up to 8–10 years) but can still eventually achieve high uptake ratios.
Continue reading ‘Limits and CO2 equilibration of near-coast alkalinity enhancement’Ocean acidification and aquacultured seaweeds: progress and knowledge gaps
Published 17 January 2023 Science ClosedTags: algae, biological response, mitigation, photosynthesis, physiology, review
This systematic review aimed to synthesise the existing studies regarding the effects of ocean acidification (OA) on seaweed aquaculture. Ocean acidification scenarios may increase the productivity of aquacultured seaweeds, but this depends on species-specific tolerance ranges. Conversely, seaweed productivity may be reduced, with ensuing economic losses. We specifically addressed questions on: how aquacultured seaweeds acclimatise with an increase in oceanic CO2; the effects of OA on photosynthetic rates and nutrient uptake; and the knowledge gaps in mitigation measures for seaweed farming in OA environments. Articles were searched by using Google Scholar, followed by Scopus and Web of Science databases, limiting the publications from 2001 to 2022. Our review revealed that, among all the OA-related studies on macroalgae, only a relatively small proportion (n < 85) have examined the physiological responses of aquacultured seaweeds. However, it is generally agreed that these seaweeds cannot acclimatise when critical biological systems are compromised. The existing knowledge gaps regarding mitigation approaches are unbalanced and have overly focused on monitoring and cultivation methods. Future work should emphasise effective and implementable actions against OA while linking the physiological changes of aquacultured seaweeds with production costs and profits.
Continue reading ‘Ocean acidification and aquacultured seaweeds: progress and knowledge gaps’Climate change amelioration by marine producers: does dominance predict impact?
Published 13 January 2023 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, mitigation, multiple factors, North Pacific, otherprocess, phanerogams, photosynthesis, temperature
Climate change threatens biodiversity worldwide, and assessing how those changes will impact communities will be critical for conservation. Dominant primary producers can alter local-scale environmental conditions, reducing temperature via shading and mitigating ocean acidification via photosynthesis, which could buffer communities from the impacts of climate change. We conducted two experiments on the coast of southeastern Alaska to assess the effects of a common seaweed species, Neorhodomela oregona, on temperature and pH in field tide pools and tide pool mesocosms. We found that N. oregona was numerically dominant in this system, covering >60% of habitable space in the pools and accounting for >40% of live cover. However, while N. oregona had a density-dependent effect on pH in isolated mesocosms, we did not find a consistent effect of N. oregona on either pH or water temperature in tide pools in the field. These results suggest that the amelioration of climate change impacts in immersed marine ecosystems by primary producers is not universal and likely depends on species’ functional attributes, including photosynthetic rate and physical structure, in addition to abundance or dominance.
Continue reading ‘Climate change amelioration by marine producers: does dominance predict impact?’Chapter 10 – Carbonate chemistry, carbon cycle, and its sequestration in aquatic system
Published 12 January 2023 Science ClosedTags: chemistry, field, mitigation, review
Carbon is the universal currency used by biota to store and expend energy. Oceans act as a reservoir for almost 30% of the atmospheric carbon dioxide. The oceans store carbon in three forms: dissolved inorganic carbon (CO2 , HCO3−, and CO32−), dissolved organic carbon (both small and large organic molecules), and particulate organic carbon (live organisms or fragments of dead plants and animals). They also store it in the form of black carbon (BC). Carbon keeps on exchanging between the aquatic and terrestrial ecosystems via atmosphere. Inorganic carbon is absorbed and released at the interface of the ocean’s surface and surrounding air, through the process of diffusion. This exchange of inorganic carbon takes place only in the form of CO 2, which forms carbonate when dissolved in seawater. The formation of carbonate allows oceans to take up and store a much larger amount of carbon than would be possible if dissolved CO2 remained in that form. Carbon is also cycled through the ocean by the biological processes of photosynthesis, respiration, and decomposition of aquatic plants. The changes in the chemistry of the ocean due to acidification have a great impact on marine life as well as corals and foraminifera. Since the concentration of carbon dioxide has increased rapidly in the last few decades, it becomes crucial for us to fully understand the carbonate processes and the various source and sink of carbon in the aquatic system in order to mitigate the negative effects of global warming and climate change.
Continue reading ‘Chapter 10 – Carbonate chemistry, carbon cycle, and its sequestration in aquatic system’Simulated impact of ocean alkalinity enhancement on atmospheric CO2 removal in the Bering Sea
Published 11 January 2023 Science ClosedTags: chemistry, field, mitigation, modeling, North Pacific, regionalmodeling
Abstract
Ocean alkalinity enhancement (OAE) has the potential to mitigate ocean acidification (OA) and induce atmospheric carbon dioxide (CO2) removal (CDR). We evaluate the CDR and OA mitigation impacts of a sustained point-source OAE of 1.67 × 1010 mol total alkalinity (TA) yr−1 (equivalent to 667,950 metric tons NaOH yr−1) in Unimak Pass, Alaska. We find the alkalinity elevation initially mitigates OA by decreasing pCO2 and increasing aragonite saturation state and pH. Then, enhanced air-to-sea CO2 exchange follows with an approximate e-folding time scale of 5 weeks. Meaningful modeled OA mitigation with reductions of >10 μatm pCO2 (or just under 0.02 pH units) extends 100–100,000 km2 around the TA addition site. The CDR efficiency (i.e., the experimental seawater dissolved inorganic carbon (DIC) increase divided by the maximum DIC increase expected from the added TA) after the first 3 years is 0.96 ± 0.01, reflecting essentially complete air-sea CO2 adjustment to the additional TA. This high efficiency is potentially a unique feature of the Bering Sea related to the shallow depths and mixed layer depths. The ratio of DIC increase to the TA added is also high (≥0.85) due to the high dissolved carbon content of seawater in the Bering Sea. The air-sea gas exchange adjustment requires 3.6 months to become (>95%) complete, so the signal in dissolved carbon concentrations will likely be undetectable amid natural variability after dilution by ocean mixing. We therefore argue that modeling, on a range of scales, will need to play a major role in assessing the impacts of OAE interventions.
Key Points
- We used regional ocean model to simulate single point-source ocean alkalinity enhancement in the Bering Sea
- The steady state carbon dioxide removal efficiency was near one in years 3+ of the simulation
- The meaningful modeled ocean acidification mitigation is confined to the region near the alkalinity addition
Plain Language Summary
The Intergovernmental Panel on Climate Change suggests that carbon dioxide (CO2) removal (CDR) approaches will be required to stabilize the global temperature increase at 1.5–2°C. In this study, we simulated the climate mitigation impacts of adding alkalinity (equivalent to 667,950 metric ton NaOH yr−1) in Unimak Pass on the southern boundary of the Bering Sea. We found that adding alkalinity can accelerate the ocean CO2 uptake and storage and mitigate ocean acidification near the alkalinity addition. It takes about 3.6 months for the Ocean alkalinity enhancement impacted area to take up the extra CO2. The naturally cold and carbon rich water in the Bering Sea and the tendency of Bering Sea surface waters to linger near the ocean surface without mixing into the subsurface ocean both lead to high CDR efficiencies (>96%) from alkalinity additions in the Bering Sea. However, even with high efficiency, it would take >8,000 alkalinity additions of the kind we simulated to be operating by the year 2100 to meet the target to stabilize global temperatures within the targeted range.
Continue reading ‘Simulated impact of ocean alkalinity enhancement on atmospheric CO2 removal in the Bering Sea’
