Long-term biogeochemical impacts of liming the ocean

Fossil fuel CO2 emissions result in large-scale long-term
perturbations in seawater chemistry. Oceans take up atmospheric CO2, and several
geo-engineering approaches have been suggested to mitigate impacts of CO2
emissions and resulting ocean acidification that are based on this property. One of
them is to enhance weathering processes to remove atmospheric CO2. This method
involves dissolving rocks (i.e. limestone) or adding strong bases (i.e. calcium
hydroxide) in the upper ocean and is termed as liming the oceans. The net effect of this
approach is to increase ocean alkalinity, thereby increasing the oceanic capacity to
store anthropogenic CO2. Another effect of adding alkalinity would be to drive seawater
to higher pH values and thus counteract the ongoing ocean acidification. However,
whereas adding bases only alter alkalinity of seawater, dissolution of carbonates
perturb both, alkalinity and dissolved inorganic carbon budgets. Thus, on longer time
scales, these two methods will likely have different biogeochemical effects in the ocean.
Here we test enduring implications of the two approaches for marine carbon cycle using
the global ocean biogeochemical model HAMOCC. In our model scenarios we add
alkalinity in the amounts proportional to fossil fuel emissions. We compare the longterm
effectiveness of the two geo-engineering approaches to decrease atmospheric
CO2.