Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?

It is increasingly apparent that adequately mitigating anthropogenic
climate interference will require ocean carbon dioxide removal (CDR)
strategies. Ocean alkalinity enhancement (OAE) is an abiotic ocean CDR
approach that aims to increase the ocean’s CO2 uptake capacity through the
dispersal of pulverized mineral or dissolved alkali into the surface
ocean.  However, OAE’s effect on marine biota is largely
unexplored. Here we investigate the impacts of moderate (~700 umol kg-1)
and high (~2700 umol kg-1) limestone-inspired alkalinity additions on two
biogeochemically and ecologically important phytoplankton functional group
representatives: Emiliania huxleyi (calcium carbonate producer) and
Chaetoceros sp. (silica producer). The growth rate and elemental ratios of
both taxa showed a neutral response to limestone-inspired alkalinization.
While our results are encouraging, we also observed abiotic mineral
precipitation, which removed nutrients and alkalinity from solution. Our
findings offer the first evaluation of biogeochemical and physiological
responses to OAE and provide evidence supporting the need for continued
research into how OAE strategies impact marine ecosystems.