Model‐Based Assessment of the CO₂ Sequestration Potential of Coastal Ocean Alkalinization

Abstract

The potential of coastal ocean alkalinization (COA), a carbon dioxide removal (CDR) climate engineering strategy that chemically increases ocean carbon uptake and storage, is investigated with an Earth system model of intermediate complexity. The CDR potential and possible environmental side effects are estimated for various COA deployment scenarios, assuming olivine as the alkalinity source in ice‐free coastal waters (about 8.6% of the global ocean's surface area), with dissolution rates being a function of grain size, ambient seawater temperature, and pH. Our results indicate that for a large‐enough olivine deployment of small‐enough grain sizes (10 µm), atmospheric CO2 could be reduced by more than 800 GtC by the year 2100. However, COA with coarse olivine grains (1000 µm) has little CO2 sequestration potential on this time scale. Ambitious CDR with fine olivine grains would increase coastal aragonite saturation Ω to levels well beyond those that are currently observed. When imposing upper limits for aragonite saturation levels (Ωlim) in the grid boxes subject to COA (Ωlim = 3.4 and 9 chosen as examples), COA still has the potential to reduce atmospheric CO2 by 265 GtC (Ωlim = 3.4) to 790 GtC (Ωlim = 9) and increase ocean carbon storage by 290 Gt (Ωlim = 3.4) to 913 Gt (Ωlim = 9) by year 2100.

Assessing carbon dioxide removal through global and regional ocean alkalinization under high and low emission pathways

“…This is consistent with Kohler et al (2013) who saw little difference in adding olivine along existing shipping tracks, versus uniformly adding it to the surface ocean. It is also consistent with regional addition studies of Ilyina et al (2013), Feng et al (2016), and Feng et al (2017 which demonstrated a global impact.…”

Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

“…Among the suggested reasons for such failures are excessive computational expenses along with sparse and noisy observational data (e.g., Lawson et al, 1996;Löptien and Dietze, 2015). In addition, or as a consequence, the discussion of the problem entails suggestions that the optimization problem is underdetermined (Matear, 1995) and that the underlying equations do not represent actual processes and conditions (Fasham et al, 1995;Fennel et al, 2001). In this study, we illustrate how deficiencies in the physical model component impact the estimation of the biogeochemical parameters (e.g., Sinha et al, 2010;Dietze and Löptien, 2013).…”

The potential environmental response to increasing ocean alkalinity for negative emissions

“…Ocean acidification has already influenced the marine environment by making it more difficult for some marine calcifiers to produce their calcium carbonate (CaCO 3 ) shells (Doney et al 2009). Artificially increasing ocean TA and the resulting increase in Ω CaCO3 would have the opposite effect, making it easier to calcify (Feng et al 2017). Therefore, AOA could potentially allow ecosystems previously affected by reduced calcification (due to ocean acidification) to return to pre-industrial calcification values (Albright et al 2016).…”

“…Although increasing ocean TA could be a way of alleviating ocean acidification, it could also increase ocean pH and Ω CaCO3 well above pre-industrial values, particularly in the regions where the alkaline minerals were added (Renforth and Henderson 2017;Feng et al 2017) (Fig. 1).…”