Oceanography | Vol. 38, No. 3
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pH and therefore a potential mitiga-
tion of OA (Doney et al., 2024; “NaOH
addition,” “Na2CO3 addition,” and
“NaHCO3 addition” lines in Figure 2;
see also Figure 3). To date, modeling
studies have suggested large uncer-
tainty in the OA mitigation potential of
OAE (Butenschön et al., 2021; Palmiéri
and Yool, 2024). On a local scale, OAE
might prove to be beneficial for miti-
gating the impact of OA, especially in
environments with less water exchange
(Khangaonkar et al., 2024). However,
this approach greatly depends on the
spatial and temporal scales and evolu-
tion of the perturbed alkalinity (Suitner
et al., 2024). A recent study suggests
that connecting OAE efficiency, air-sea
gas exchange, and ocean circulation
could be a useful tool for considering
local implications for OA (Zhou et al.,
2025). Once equilibrated, the only ben-
efit to OA is an offset from further acid-
ification from continued CO2 uptake
(i.e., more CO2 can go into the ocean
without causing further OA), rather
than a reversal (i.e., removing CO2 and
increasing pH back to historic levels)
(Mongin et al., 2021). Interestingly, if
OAE improves the seawater chemistry
for shell-building organisms through
raising calcium carbonate satura-
tion states, increased net calcification
rates (one of the key ecological pro-
cesses impacted by OA) would con-
sume alkalinity and increase seawater
pCO2, thus potentially negating any
carbon removal efforts at local (habitat)
scales (Renforth and Henderson, 2017).
The type of alkalinity used, and the
method and rate of OAE addition, will
all determine OAE’s ability to mitigate
OA (Figure 2). Furthermore, if OAE is
carried out incorrectly (i.e., adding too
much alkalinity too rapidly), it could
increase the carbonate mineral satu-
ration state and stimulate precipita-
tion (Renforth and Henderson, 2017),
thereby consuming alkalinity and
increasing pCO2 levels. In this scenario,
OAE could exacerbate OA by reducing
seawater’s buffering capacity. Although
FIGURE 3. Schematic of the air-sea equilibrium and carbonate chemistry of seawater before, during,
and after mCDR interventions, highlighting potential connections to ocean acidification (OA) as indi-
cated by the dark red annotations. “OA↓” indicates mitigation of OA (elevated pH), “OA =” indicates no
change in OA, “OA=/↓” indicates no change/possible mitigation of OA (elevating pH), and “OA↓?” indi-
cates possible exacerbation of OA (lower pH). For the biological mCDR column, long-term storage is
dependent on the vertical partitioning of the biological carbon pump, and where the organic matter
finally ends up. It is highly likely that the organic matter remineralizes back to CO2 in the deep ocean,
then potentially exacerbates OA. For the other two columns, long-term storage is likely to be stable in
DIC form (OAE) or in geological storage (DOCCS), where there is low likelihood of leakage back into the
marine system as CO2 (which could then exacerbate OA).