“Viability of Greenhouse Gas Removal via Artificial Addition of Volcanic Ash to the Ocean”, 2020-12-01 (; similar):
Mitigating human contributions to climate change is a highly debated topic, as it becomes evident that many nations do not adhere to optional reductions in global emission. Substantial research is taking place into negative carbon technologies that actively reduce the amount of atmospheric carbon dioxide (CO2) via greenhouse gas removal (GGR). Various GGR methods have been proposed, from reforestation to ocean fertilisation.
This article discusses advantages of an approach based on enhanced input of tephra [volcanic ash] to the ocean, to increase the drawdown of atmospheric CO2. Natural addition of tephra to the ocean results in preservation of enhanced organic matter in sediment. Hence, augmenting its delivery should raise the level of sequestration.
Calculations indicate that offshore tephra addition could sequester 2,750 tonnes of CO2 per 50,000 tonnes of ash delivered (a typical bulk carrier’s capacity). The cost is estimated as ~$55 per tonne of CO2 sequestered and is an order of magnitude cheaper than many proposed GGR technologies. Further advantages include: tephra addition is simply an augmentation of a natural Earth process, it is a low technology approach that requires few developments, and it may sequester carbon for thousands of years.
Hence, offshore tephra addition warrants further investigation to assess its viability.
[Keywords: greenhouse gas removal, geoengineering, offshore tephra addition, volcanic ash, diagenesis, climate change]
…Tephra releases nutrients, such as dissolved Iron (Fe), to surface waters when it falls into the oceans, and may thus stimulate biological productivity where availability of nutrients limits phytoplankton growth ( et al 2011). This process has been studied extensively (see and et al 2010 for reviews). For example, phytoplankton blooms occurred when the eruption of Kasatochi volcano deposited tephra in the nutrient-poor NE Pacific Ocean ( et al 2010; et al 2011), in the vicinity of the Mariana Islands following the 2003 Anatahan eruption ( et al 2011), after the eruption of Miyakejima in 2000 ( et al 2004), and potentially in the Southern Pacific after the eruption of Pinatubo in 1991 (1993). Other research suggested that the deposition of subduction zone-related ash may play a role in controlling productivity ( et al 2007). In each case, the increased productivity sequestered CO2 from the ocean-atmosphere. The 2008 eruption of Kasatochi, for example, led to the export of ~0.01 Pg carbon from the upper ocean ( et al 2010). Carbon was removed from the upper oceans when phytoplankton (and their consumers) settled out of the upper ocean and into the deep ocean (the ‘biological pump’; 2006). In addition to accelerating the rate of the biological pump (Figure 2), tephra deposition in the surface oceans also likely enhances the transport of organic carbon (Corg) from surface oceans into deeper water, because plankton debris may become physically associated with the negatively buoyant particles (eg. et al 2011). This process leads to the incorporation of dense, Fe-rich dust (and by analogy tephra) in algal colonies, ballasting the tephra and enhancing sinking rates ( et al 2017).
…Quarrying of recent tephra (optimal for this proposed method) provides aggregate for cement works and road surfaces, but supplies are not limiting. Large recent deposits of basaltic tephra are located at active volcanoes across the globe (Figure 3). In addition, bentonite clay (diagenetically altered tephra) mining is well-established (2009), so novel, energy-intensive, extraction techniques are not required. Most tephra extraction occurs in open pits using bucket loaders. It would only require sorting of the unconsolidated tephra to grain size <63 μm, the fraction containing most Fe-rich minerals
…The only processing of the tephra before its use would be light crushing and sorting. Spreading tephra over the ocean would require infrastructure, including loading terminals and adapted ships (ie. with mechanisms for tephra release), but land transport costs would be low because most volcanoes are located close to the oceans (Figure 3). Marine vessels require an energy source, but the use of redundant coal barges could reduce CO2 emissions. Freshly deposited tephra is unconsolidated and can be removed and loaded into transport using conventional excavators and trucks.