Abstract
Ocean Alkalinity Enhancement (OAE) is a proposed strategy for reducing atmospheric carbon dioxide (CO2) for the purpose of mitigating climate change. It involves altering the carbon chemistry of the surface ocean, which is difficult to predict the consequences of on a large scale. Early research suggests local and seasonal variability in the response of primary producers to OAE. To investigate how this may apply to phytoplankton communities in one local environment, a microcosm experiment was conducted using nine 55 L tanks of water collected from the surface of Otago Harbour. Three were treated with sodium hydroxide, simulating conditions produced shortly after OAE, and another three were treated with sodium hydroxide and sodium hydrogen carbonate to simulate OAE after equilibration with the atmosphere. All were incubated at 15° C for 20 days and various chemical and biological parameters were monitored. Most parameters showed little or no difference between treatment groups, but some (biogenic silica, dissolved silicate, chlorophyll a) suggested a possible reduction in diatom biomass under OAE conditions. These results are promising for the viability of OAE and indicate potential areas of focus for future research.