Ocean fertilization does not increase the acidity of surface waters.

Ocean fertilization temporarily lowers ocean acidity in the crucial upper waters. However, as soon as the CO2 concentration is lowered there, more will “flux” in from the atmosphere. This is the mechanism that explains how ocean fertilization could lower atmospheric CO2.

The pH of the oceans is alkaline. It ranges from 7.8-8.5; and has been so for hundreds of millions of years. CO2 acts like an acid when it dissolves in water. Henry’s Law of Partial Pressures explains why increasing CO2 emissions in the atmosphere will cause an increase concentration of CO2 in the oceans. This has been called “ocean acidification.” Even this slight increase in acidity can have a profound effect on corals and other organisms that make skeletal material out of calcium carbonate, which is harder to produce as acidity increases.

When people speak of ocean acidity, they are generally speaking about a lower pH in the upper 100 meters, where the majority of marine organisms (including microorganisms such as coral and phytoplankton) live. Many of these organisms cannot tolerate the higher ph levels caused by excessive CO2. Our burning of fossil fuels is responsible for the excess CO2 in the upper ocean.

As fertilization stimulates phytoplankton growth, CO2 is removed from surface waters by photosynthesis to form the organic material of their cells-thereby lowering acidity. However, this improvement is short-lived. According to Henry’s Law of Partial Pressures, the atmosphere must continuously re-equilabrate with the ocean, allowing more of the atmospheric CO2 causing global warming to enter the surface waters. This process happens over approximately 6 months, and is the reason why ocean fertilization has the effect of lowering atmospheric CO2.

A portion of the biomass created at the surface eventually dies and sinks as dead plankton organisms or as fecal pellets from larger zooplankton grazers. This process takes the carbon to the deep ocean, where the majority becomes ‘remineralized’ across a range of depths-beginning the long process of breaking the organic material back down into basic nutrients. This process is known to oceanographers as the “Biological Pump.” Over more than one billion years, the biological pump has contributed to the accumulation of approximately 85% of all mobile carbon in the deep ocean.

Whereas there are only 750 GtC (billions of tonnes of carbon) in the atmosphere, there are nearly 40,000 GtC in the deep ocean. Over the last 100 years, we have raised atmospheric concentrations by 35% from 280ppm (pre-industrial) to 380ppm (present-day), or approximately 260 GtC

If this same 260 GtC were moved to the deep ocean, it would increase the carbon concentration there by less than 1%. Ocean acidity from increased carbon at depth is not a concern.

Eventually, whether we assist or not, natural processes will move the large majority of the present excess atmospheric CO2 into the deep ocean — we are proposing to help that process happen more quickly.