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Review
. 2017 Apr;13(4):20160905.
doi: 10.1098/rsbl.2016.0905.

Negative CO2 emissions via enhanced silicate weathering in coastal environments

Filip J R Meysman  1   2 , Francesc Montserrat  3
Affiliations
Review

Negative CO2 emissions via enhanced silicate weathering in coastal environments

Filip J R Meysman et al. Biol Lett. 2017 Apr.

Abstract

Negative emission technologies (NETs) target the removal of carbon dioxide (CO2) from the atmosphere, and are being actively investigated as a strategy to limit global warming to within the 1.5-2°C targets of the 2015 UN climate agreement. Enhanced silicate weathering (ESW) proposes to exploit the natural process of mineral weathering for the removal of CO2 from the atmosphere. Here, we discuss the potential of applying ESW in coastal environments as a climate change mitigation option. By deliberately introducing fast-weathering silicate minerals onto coastal sediments, alkalinity is released into the overlying waters, thus creating a coastal CO2 sink. Compared with other NETs, coastal ESW has the advantage that it counteracts ocean acidification, does not interfere with terrestrial land use and can be directly integrated into existing coastal management programmes with existing (dredging) technology. Yet presently, the concept is still at an early stage, and so two major research challenges relate to the efficiency and environmental impact of ESW. Dedicated experiments are needed (i) to more precisely determine the weathering rate under in situ conditions within the seabed and (ii) to evaluate the ecosystem impacts-both positive and negative-from the released weathering products.

Keywords: carbon dioxide removal; climate change; enhanced weathering; marine ecosystems; olivine.

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Conflict of interest statement

The authors have no competing interests.

Figures

Figure 1.
Figure 1.
Enhanced silicate weathering in coastal systems is a four-stage process. [1] Olivine dissolution takes place at the surface of the individual mineral particles, releasing reaction products (Mg2+, dissolved silicate, alkalinity and trace metals) into the interstitial pore solution. [2] An additional efflux of alkalinity is released from the sediment [3]. The alkalinity increase of the surface waters induces a CO2 transfer across the air–sea interface. [4] Dissolution products are exchanged with the open ocean over short time scales (0.1–1 yr) and exported to the deep sea over longer time scales (100–1000 yr). Two ESW application scenarios have been proposed: (a) spreading coarse particles into high-dynamic shelf environments where particles are crushed during bedload transport (‘shelf milling’) and (b) spreading finer olivine sand onto beaches and shallows, where dissolution is enhanced through biotic processes in the seabed (‘benthic weathering engine’). AT, total alkalinity; DIC, dissolved inorganic carbon; JA, alkalinity efflux from the sediment; Rdiss, dissolution rate of olivine.
Figure 2.
Figure 2.
The accumulation of reaction products (alkalinity, pH, silicate, nickel) from olivine dissolution within the coastal bottom water. The accumulation formula image (difference in concentration with and without ESW) is plotted as a function of the water residence time for four different average water depths. For reference, the black lines indicate typical values for the ambient concentration of dissolved silicon and nickel in temperate coastal waters.
See this image and copyright information in PMC

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