Negative CO 2 emissions via enhanced silicate weathering in coastal environments

Hartmann

et al. 2017

Environ. Sci. Technol.

Self Cite

191

128

Enhanced weathering of (ultra)basic silicate rocks such as olivine-rich dunite has been proposed as a large-scale climate engineering approach. When implemented in coastal environments, olivine weathering is expected to increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marine olivine weathering and its effect on seawater–carbonate chemistry remain poorly understood. Here, we present results from batch reaction experiments, in which forsteritic olivine was subjected to rotational agitation in different seawater media for periods of days to months. Olivine dissolution caused a significant increase in alkalinity of the seawater with a consequent DIC increase due to CO2 invasion, thus confirming viability of the basic concept of enhanced silicate weathering. However, our experiments also identified several important challenges with respect to the detailed quantification of the CO2 sequestration efficiency under field conditions, which include nonstoichiometric dissolution, potential pore water saturation in the seabed, and the potential occurrence of secondary reactions. Before enhanced weathering of olivine in coastal environments can be considered an option for realizing negative CO2 emissions for climate mitigation purposes, these aspects need further experimental assessment.

Section: Discussionmentioning

confidence: 99%

Olivine Dissolution in Seawater: Implications for CO₂ Sequestration through Enhanced Weathering in Coastal Environments

Montserrat¹,

Hartmann

et al. 2017

Environ. Sci. Technol.

Self Cite

191

128

“…A number of studies investigate the potential of adding naturally occurring minerals directly to the land surface [ Hartmann et al , ; Hartmann and Kempe , ; Köhler et al , ; Manning , ; Manning et al , ; Moosdorf et al , ; Renforth , ; Schuiling and Krijgsman , ; Taylor et al , ; ten Berge et al , ), coastal environments ( Hangx and Spiers , ; Schuiling and de Boer , ; Montserrat et al , ; Meysman and Montserrat , ], and the open ocean [ Harvey , ; Köhler et al , ]. The feasibility of such approaches is still highly contested given the slower dissolution kinetics at ambient temperatures and pressures, and the solubility limits of naturally occurring minerals.…”

Section: Introductionmentioning

confidence: 99%

“…If ocean HCO 3 − and CO 3 2− were the sole repository of the carbon, then others argue that such an approach may be limited by the saturation state or environmental pH limits of the rain/river water [ Köhler et al , ]. It may be possible to use the constantly refreshed water of coastal environments, in which wave action could increase the attrition of mineral particles [ Schuiling and de Boer , ; Montserrat et al , ; Meysman and Montserrat , ]. However, the slightly alkaline pH of ocean water is likely to retard dissolution kinetics so that very small particles are needed [ Hangx and Spiers , ].…”

Section: Introductionmentioning

confidence: 99%

Assessing ocean alkalinity for carbon sequestration

Henderson

2017

Reviews of Geophysics

290

263

Over the coming century humanity may need to find reservoirs to store several trillions of tons of carbon dioxide (CO2) emitted from fossil fuel combustion, which would otherwise cause dangerous climate change if it were left in the atmosphere. Carbon storage in the ocean as bicarbonate ions (by increasing ocean alkalinity) has received very little attention. Yet recent work suggests sufficient capacity to sequester copious quantities of CO2. It may be possible to sequester hundreds of billions to trillions of tons of C without surpassing postindustrial average carbonate saturation states in the surface ocean. When globally distributed, the impact of elevated alkalinity is potentially small and may help ameliorate the effects of ocean acidification. However, the local impact around addition sites may be more acute but is specific to the mineral and technology. The alkalinity of the ocean increases naturally because of rock weathering in which >1.5 mol of carbon are removed from the atmosphere for every mole of magnesium or calcium dissolved from silicate minerals (e.g., wollastonite, olivine, and anorthite) and 0.5 mol for carbonate minerals (e.g., calcite and dolomite). These processes are responsible for naturally sequestering 0.5 billion tons of CO2 per year. Alkalinity is reduced in the ocean through carbonate mineral precipitation, which is almost exclusively formed from biological activity. Most of the previous work on the biological response to changes in carbonate chemistry have focused on acidifying conditions. More research is required to understand carbonate precipitation at elevated alkalinity to constrain the longevity of carbon storage. A range of technologies have been proposed to increase ocean alkalinity (accelerated weathering of limestone, enhanced weathering, electrochemical promoted weathering, and ocean liming), the cost of which may be comparable to alternative carbon sequestration proposals (e.g., $20–100 tCO2−1). There are still many unanswered technical, environmental, social, and ethical questions, but the scale of the carbon sequestration challenge warrants research to address these.

“…Coastal environments are a favourable site for alkalinity addition by providing geochemical and environmental benefits over open ocean AOA (Meysman and Montserrat 2017;Schuiling and de Boer 2010). An important feature of coastal ecosystems across the globe is red calcifying macroalgae (Corallinales; Akioka et al 1999).…”

Section: Introductionmentioning

confidence: 99%

The potential environmental response to increasing ocean alkalinity for negative emissions

Gore

Mitig Adapt Strateg Glob Change

Perkins

2018

The negative emissions technology, artificial ocean alkalinization (AOA), aims to store atmospheric carbon dioxide (CO 2 ) in the ocean by increasing total alkalinity (TA). Calcium carbonate saturation state (ΩCaCO 3 ) and pH would also increase meaning that AOA could alleviate sensitive regions and ecosystems from ocean acidification. However, AOA could raise pH and ΩCaCO 3 well above modern-day levels, and very little is known about the environmental and biological impact of this. After treating a red calcifying algae (Corallina spp.) to elevated TA seawater, carbonate production increased by 60% over a control. This has implication for carbon cycling in the past, but also constrains the environmental impact and efficiency of AOA. Carbonate production could reduce the efficiency of CO 2 removal. Increasing TA, however, did not significantly influence Corallina spp. primary productivity, respiration, or photophysiology. These results show that AOA may not be intrinsically detrimental for Corallina spp. and that AOA has the potential to lessen the impacts of ocean acidification. However, the experiment tested a single species within a controlled environment to constrain a specific unknown, the rate change of calcification, and additional work is required to understand the impact of AOA on other organisms, whole ecosystems, and the global carbon cycle.