Giving Geo-Engineering Another Go: Dumping Limestone into the Oceans to Fight Acidification

limestone layers

Image courtesy of pierreyves0 via flickr

Unlike iron fertilization, whose intended aim is to stimulate large phytoplankton blooms in the hopes of increasing atmospheric carbon dioxide draw-down, the main objective of the University of Toronto's Danny Harvey seems far simpler (hewing closely to basic chemistry principles): to neutralize increased ocean acidity by adding a base, limestone. To do so, he proposed dumping huge quantities of powdered limestone -- around 4b tons every year -- into the oceans; his findings were just published in the Journal of Geophysical Research (h/t Discovery News' Jessica Marshall). A self-regulating carbonate buffering system normally helps keep the ocean's pH constant -- around 8.1 -- by maintaining an equilibrium between the four forms of dissolved carbon dioxide: the gas itself, carbonate ions, bicarbonate ions and carbonic acid. This delicate balance allows the oceans to absorb large amounts of carbon dioxide without much variation in seawater chemistry.

However, the rapid build-up in carbon dioxide levels over the last few decades now threatens to overwhelm the system, with some scientists projecting that pH levels could drop 0.5 units by 2100 -- wiping out most of the world's coral reefs and adversely affecting the majority of marine organisms.

Adding limestone (or calcium carbonate) would have the dual effect of mitigating the process of ocean acidification and increasing carbon sequestration, Harvey discovered, though the latter would predominate. The reason is that the limestone, by bolstering the carbonate buffering system, allows the surface waters to take up more carbon dioxide. As more is drawn down, however, the neutralizing effect of the calcium carbonate begins to diminish -- resulting in an overall slight decrease in acidity.

This process would take a long time: According to Harvey, it could take several decades (and many hundreds of billions of tons of limestone) before the limestone accomplishes its objective -- and that's assuming everything goes according to his predictions. Adding the limestone to regions of active upwelling could eventually lead to the sequestration of an additional 0.3b tons of carbon a year, he claims.

Even assuming its ecological side effects are relatively benign (a big "if"), the scheme has little chance of being implemented, says Ken Caldeira of Stanford University's Carnegie Institution, who described Harvey's plan as "unrealistic" and a mere "theoretical possibility."

Via ::Discovery News: Ocean Science Experiment Could Fight Acidification (news website)

See also: ::A Novel Strategy to Counter Ocean Acidification, ::Some (Phytoplankton) Like it Acidic