A spoonful of limestone

In the last blog I mentioned the fact that SRM measures won't have the desired effects of reduced the amount of ocean acidification which is currently increasing.

The acidity of the ocean is currently increasing due to the fact that as more CO₂ is taken up by the oceans the buffering capacity of the oceans decreases making the oceans more acidic. 

In 2008, Harvey conducted a study that investigated the feasibility of enhancing the absorption of CO2 from the atmosphere by adding calcium carbonate (CaCO3) powder to the ocean. 

Rau and Caldeira (1999), Caldeira and Rau (2000), and Rau et al. (2007) first suggested this idea. They suggested reacting captured fossil fuel CO2 with limestone in reaction chambers on land before releasing it into the ocean, rather than directly injecting captured CO2 into the deep ocean, as in the conventional ocean carbon sequestration concept (IPCC, 2005). However their scheme avoids the impacts on ocean acidity and the eventual outgassing of about 15% of the injected CO2 that would occur with conventional oceanic carbon sequestration but would require large infrastructure efforts.

However Harvey's method would have the desired outcome of partially reversing the acidification of the ocean and the resultant decrease in calcite supersaturation resulting from the absorption of anthropogenic CO2. 

He states that CaCO3 could be added to the surface layer in regions where the depth of the boundary between supersaturated and unsaturated water is relatively shallow (250–500 m) and where the upwelling velocity is large.

The CaCO3 would dissolve within a few 100 m depth below the saturation horizon, and the dissolution products would enter the mixed layer within a few years to decades, facilitating further absorption of CO2 from the atmosphere based upon a study done by Broecker and Takahashi in 1978. 

This absorption of CO2 would largely offset the increase in mixed layer pH and carbonate supersaturation resulting from the upwelling of dissolved limestone powder (Wunsch and Heimbach, 2000).

Harvey later goes on to conclude that Geographically optimal application of 4 billion t of CaCO3 a-1 (0.48 Gt C a-1) could induce absorption of atmospheric CO2 at a rate of 600 Mt CO2 a-1 after 50 years, 900 Mt CO2 a-1 after 100 years, and 1050 Mt CO2 a-1 after 200 years. 

Those statistics prove promising however there are large caveats which can be placed on a scheme like this which I will discuss later.

Thanks again,

Sam.