Posts Tagged 'mitigation'

Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities

Scientists increasingly agree that carbon dioxide removal will be needed, alongside deep emissions cuts, to stave off the worst impacts of climate change. A wide variety of technologies and strategies have been proposed to remove carbon dioxide from the atmosphere. To date, most research has focused on terrestrial-based approaches, but they often have large land requirements, and may present other risks and challenges. As such, there is growing interest in using the oceans, which have already absorbed more than a quarter of anthropogenic carbon dioxide emissions, and could become an even larger carbon sink in the future.

This paper explores two ocean-based carbon dioxide removal strategies—ocean alkalinity enhancement and seaweed cultivation. Ocean alkalinity enhancement involves adding alkalinity to ocean waters, either by discharging alkaline rocks or through an electrochemical process, which increases ocean pH levels and thereby enables greater uptake of carbon dioxide, as well as reducing the adverse impacts of ocean acidification. Seaweed cultivation involves the growing of kelp and other macroalgae to store carbon in biomass, which can then either be used to replace more greenhouse gas-intensive products or sequestered.

Continue reading ‘Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities’

Climate change mitigation effects: how do potential CO2 leaks from a sub-seabed storage site in the Norwegian Sea affect Astarte sp. bivalves?


  • Acidification and recovery were assessed with high-pressure bioassays.
  • No mortality was reported for Astarte sp. for a pH 7.0 scenario.
  • Normal growth of shell length was recorded after CO2 exposure and a recovery period.


Carbon capture and storage (CCS) is one of the most promising mitigation strategies for reducing the emissions of carbon dioxide (CO2) to the atmosphere and may substantially help to decelerate global warming. There is an increasing demand for CCS sites. Nevertheless, there is a lack of knowledge of the environmental risk associated with potential leakage of CO2 from the storage sites; and even more, what happens when the seepage stops. Can the environment return to the initial equilibrium? Potential effects on native macrofauna were studied under a scenario of a 50-day CO2 leakage, and the subsequent leak closure. To accomplish the objective, Trondheim Fjord sediments and clams were exposed to an acidified environment (pH 6.9) at 29 atm for 7 weeks followed by a 14-day recovery at normal seawater conditions (pH 8.0, 29 atm). Growth and survival of clams exposed to pressure (29 atm) and reduced pH (6.9) did not significantly differ from control clams kept at 1 atm in natural seawater. Furthermore, bioaccumulation of elements in the soft tissue of clams did not register significant variations for most of the analysed elements (Cd, Cr, Pb, and Ti), while other elements (As, Cu, Fe, Ni) had decreasing concentrations in tissues under acidified conditions in contrast to Na and Mg, which registered an uptake (Ku) of 111 and 9.92 μg g−1dw d−1, respectively. This Ku may be altered due to the stress induced by acidification; and the element concentration being released from sediments was not highly affected at that pH. Therefore, a 1 unit drop in pH at the seafloor for several weeks does not appear to pose a risk for the clams.

Continue reading ‘Climate change mitigation effects: how do potential CO2 leaks from a sub-seabed storage site in the Norwegian Sea affect Astarte sp. bivalves?’

Alkalinization scenarios in the Mediterranean Sea for efficient removal of atmospheric CO2 and the mitigation of ocean acidification

It is now widely recognised that in order to reach the target of limiting global warming below 2 °C above pre-industrial levels (as the objective of the Paris agreement) there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. Relatively few studies have assessed the mitigation capacity of ocean-based Negative Emission Technologies (NET) and the feasibility of their implementation on a larger scale to support efficient implementation strategies of CDR. This study investigates the case of marine alkalinisation, which has the additional potential of contrasting the ongoing acidification resulting from increased uptake of atmospheric CO2 by the seas. More specifically, we present an analysis of ocean alkalinisation applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealised spatially homogenous scenarios of alkalinisation as done in previous studies, we use a set of numerical simulations of alkalinisation based on current shipping routes to quantitatively assess the alkalinisation efficiency via a coupled physical-biogeochemical model over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinisation, and of neutralising the mean surface acidification trend of the baseline scenario without alkalinisation over the same time span. These levels are achieved via two different strategies: a first approach applying constant annual discharge of 200Mt Ca(OH)2 over the alkalinisation period and a second approach with gradually increasing discharge proportional to the surface pH trend of the baseline scenario reaching similar amounts of annual discharge by the end of the alkalinisation period. We demonstrate that via the latter approach it is possible to stabilise the mean surface pH at present day values and substantially increase the potential to counteract acidification relative to the alkalinity added while the carbon uptake efficiency is only marginally reduced. Nevertheless, significant local alterations of the surface pH persist, calling for an investigation of the physiological and ecological implications of the extent of these alterations to the carbonate system in the short to medium term in order to support a safe, sustainable application of this CDR implementation.

Continue reading ‘Alkalinization scenarios in the Mediterranean Sea for efficient removal of atmospheric CO2 and the mitigation of ocean acidification’

Seaweed farms provide refugia from ocean acidification

Seaweed farming has been proposed as a strategy for adaptation to ocean acidification, but evidence is largely lacking. Changes of pH and carbon system parameters in surface waters of three seaweed farms along a latitudinal range in China were compared, on the weeks preceding harvesting, with those of the surrounding seawaters. Results confirmed that seaweed farming is efficient in buffering acidification, with Saccharina japonica showing the highest capacity of 0.10 pH increase within the aquaculture area, followed by Gracilariopsis lemaneiformis (ΔpH = 0.04) and Porphyra haitanensis (ΔpH = 0.03). The ranges of pH variability within seaweed farms spanned 0.14-0.30 unit during the monitoring, showing intense fluctuations which may also help marine organisms adapt to enhanced pH temporal variations in the future ocean. Deficit in pCO2 in waters in seaweed farms relative to control waters averaged 58.7 ± 15.9 μatm, ranging from 27.3 to 113.9 μatm across farms. However, ΔpH did not significantly differ between day and night. Dissolved oxygen and Ωarag were also elevated in surface waters at all seaweed farms, which are benefit for the survival of calcifying organisms. Seaweed farming, which unlike natural seaweed forests, is scalable and is not dependent on suitable substrate or light availability, could serve as a low-cost adaptation strategy to ocean acidification and deoxygenation and provide important refugia from ocean acidification.

Continue reading ‘Seaweed farms provide refugia from ocean acidification’

Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states


  • Harmonized simulation of DO, pH, and Y2095 climate change impacts in the Salish Sea
  • A 52-fold increase in exposure and near-bed pelagic species to hypoxic waters in Y2095
  • Ocean acidification projections for Y2095 indicate ≈ 20 −114% increase in water column (ΩA) <1)
  • Primary productivity propagation to zooplankton projected for Y2095 with ≈ 13%−25% increases.
  • Eelgrass sensitive to stressors and potential for loss of eelgrass biomass in the future.


Future projections based on the IPCC high emissions scenario RCP8.5 have previously shown that the Pacific Northwest coastal waters will be subjected to altered ocean states in the upwelled shelf waters, resulting in higher primary productivity and increased regions of hypoxia and acidification in the inner estuarine waters such as the Salish Sea. However, corresponding effects on the lower trophic levels and submerged aquatic vegetation have not yet been quantified. Supported by new synoptic field data, explicit coupled simulation of algae, zooplankton, and eelgrass biomass was accomplished for the first time in the Salish Sea. We re-applied the improved model to evaluate future ecological response and examined potential algal species shift, but with the effects of zooplankton production, metabolism, and predation-prey interactions included. We also evaluated the role of eelgrass with respect to potential for improvements to dissolved oxygen and pH levels and as a mitigation measure against hypoxia and ocean acidification. The results re-confirm the possibility that there could be a substantial area-days increase (≈52-fold) in exposure of benthic and near-bed pelagic species to hypoxic waters in 2095. The projections for ocean acidification similarly indicate ≈ 20 -114% increase in exposure to lower pH corrosive waters with aragonite saturation state ΩA <1. Importantly, projected increase in primary productivity was shown to propagate to higher trophic levels, with ≈ 13% and 25% increases in micro and mesozooplankton biomass levels. However, the preliminary results also point to sensitivity of the eelgrass model to environmental stressor and potential loss eelgrass biomass in the future.

Continue reading ‘Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states’

Futureproofing the green-lipped mussel aquaculture industry against ocean acidification

Two mitigation strategies – waste shell and aeration – were tested in field experiments to see how effective they are at mitigating acidification around mussel farms. This report outlines the results and recommendations from this research. 

Primary results:

  • The inner Firth of Thames currently experiences the lowest seasonal pH of the sites monitored, with a daily minimum of 7.84 (7.79–7.96) in autumn, with short-term (15-minute) pH minima as low as 7.2. Time-series data in the inner and outer Firth of Thames, and also on a mussel farm in the western Firth, show episodic declines in carbonate saturation to the critical carbonate saturation state ΩAR = 1.0 at which solid aragonite (the form of carbonate in mussel shells) will start to dissolve. Consequently, mussels in the Firth of Thames experience episodic corrosive conditions.
  • The mean pH in the Marlborough Sounds region is projected to decrease by 0.15–0.4 by 2100 depending on future emission scenario. The corresponding decline of 0.5–1.25 in the saturation state of aragonite (ΩAR), results in the critical threshold of ΩAR =1 being reached by 2100 under the worst-case scenario. These projections are based only on future CO2 emission scenarios and do not consider other coastal sources of acidity in coastal waters which may also alter in the future.

Continue reading ‘Futureproofing the green-lipped mussel aquaculture industry against ocean acidification’

Benefits and gaps in area-based management tools for the ocean Sustainable Development Goal

Sustainable Development Goal (SDG) 14 provides a vision for the world’s oceans; however, the management interventions that are needed to achieve SDG 14 remain less clear. We assessed the potential contributions of seven key area-based management tools (such as fisheries closures) to SDG 14 targets. We conducted a rapid systematic review of 177 studies and an expert opinion survey to identify evidence of the ecological, social and economic outcomes from each type of tool. We used these data to assess the level of confidence in the outcomes delivered by each tool and qualitatively scored how each tool contributes to each target. We demonstrate that a combination of tools with diverse objectives and management approaches will be necessary to achieve all of the SDG 14 targets. We highlight that some tools, including fully and partially protected areas and locally managed marine areas, may make stronger contributions to SDG 14 compared with other tools. We identified gaps in the suitability of these tools to some targets, particularly targets related to pollution and acidification, as well as evidence gaps for social and economic outcomes. Our findings provide operational guidance to support progress toward SDG 14.

Continue reading ‘Benefits and gaps in area-based management tools for the ocean Sustainable Development Goal’

Hysteresis of the Earth system under positive and negative CO2 emissions

Carbon dioxide removal (CDR) from the atmosphere is part of all emission scenarios of the IPCC that limit global warming to below 1.5 degrees C. Here, we investigate hysteresis characteristics in 4x pre-industrial atmospheric CO2 concentration scenarios with exponentially increasing and decreasing CO2 using the Bern3D-LPX Earth system model of intermediate complexity. The equilibrium climate sensitivity (ECS) and the rate of CDR are systematically varied. Hysteresis is quantified as the difference in a variable between the up and down pathway at identical cumulative carbon emissions. Typically, hysteresis increases non-linearly with increasing ECS, while its dependency on the CDR rate varies across variables. Large hysteresis is found for global surface air temperature (Delta SAT), upper ocean heat content, ocean deoxygenation, and acidification. We find distinct spatial patterns of hysteresis: Delta SAT exhibits strong polar amplification, hysteresis in O-2 is both positive and negative depending on the interplay between changes in remineralization of organic matter and ventilation. Due to hysteresis, sustained negative emissions are required to return to and keep a CO2 and warming target, particularly for high climate sensitivities and the large overshoot scenario considered here. Our results suggest, that not emitting carbon in the first place is preferable over carbon dioxide removal, even if technologies would exist to efficiently remove CO2 from the atmosphere and store it away safely.

Continue reading ‘Hysteresis of the Earth system under positive and negative CO2 emissions’

CO2 reduction for C2+ in seawater using a graphitic frustrated Lewis pair catalyst

Ocean acidification due to the absorption of 40% of the world’s anthropogenic CO2 emissions severely affects the faltering marine ecosystem and the economy. However, there are few reports on reducing CO2 dissolved in seawater. Herein, we introduce an electrochemical CO2 reduction battery system for use in seawater with a graphitic frustrated Lewis pair catalytic cathode doped with boron and nitrogen (BN-GFLP). BN-GFLP converts CO2 dissolved in seawater to multi-carbon (C2+) products during the discharge process, thus increasing the pH of intentionally acidified seawater from 6.4 to 8.0 with more than 87% Faradaic efficiency. In computational chemistry and spectroscopy, BN-GFLP binds CO2 in a unique manner that enables exothermic C–C coupling pathway to deliver 95% selectivity for valuable C2+ products. Based on our results, we suggest a molecular design strategy for next-generation CO2 reduction catalysts for both green oceans and the atmosphere.

Continue reading ‘CO2 reduction for C2+ in seawater using a graphitic frustrated Lewis pair catalyst’

Drivers of biogeochemical variability in a central California kelp forest: implications for local amelioration of ocean acidification

Kelp forests are among the world’s most productive marine ecosystems, and they have the potential to locally ameliorate ocean acidification (OA). In order to understand the contribution of kelp metabolism to local biogeochemistry, we must first quantify the natural variability and the relative contributions of physical and biological drivers to biogeochemical changes in space and time. We deployed an extensive instrument array in Monterey Bay, CA, inside and outside of a kelp forest to assess the degree to which giant kelp (Macrocystis pyrifera) locally ameliorates present‐day acidic conditions which we expect to be exacerbated by OA. Temperature, pH, and O2 variability occurred at semidiurnal, diurnal (tidal and diel), and longer upwelling event periods. Mean conditions were driven by offshore wind forcing and the delivery of upwelled water via nearshore internal bores. While near surface pH and O2 were similar inside and outside the kelp forest, surface pH was elevated inside the kelp compared to outside, suggesting that the kelp canopy locally increased surface pH. We observed the greatest acidification stress deeper in the water column where pCO2 reached levels as high as 1300 μatm and aragonite undersaturation (ΩAr <1) occurred on several occasions. At this site, kelp canopy modification of seawater properties, and thus any ameliorating effect against acidification is greatest in a narrow band of surface water. The spatial disconnect between stress exposure at depth and reduction of acidification stress at the surface warrants further assessment of utilizing kelp forests as provisioners of local OA mitigation.

Continue reading ‘Drivers of biogeochemical variability in a central California kelp forest: implications for local amelioration of ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book