The effects of ocean acidification (OA) are expected to be manifest over a broad range of spatial and temporal scales throughout the world ocean as the pH drops from the pre-industrial value of 8.2 to 7.8 by the year 2100. Calcifying plankton (like other biocalcifiers such as corals and shellfish) are expected to be strongly affected by OA because of their need for saturating carbonate conditions, which enables precipitation of calcium carbonate. Within the calcifying plankton, coccolithophores precipitate the smallest calcium carbonate particles (coccoliths), which are some of the strongest light-scattering particles in the sea. Thus, anything that will affect coccolithophore calcification (including OA) will likely affect the optical properties of the sea. Here, we describe the optical properties of coccolithophores and interpret some historical observations within the context of OA. Then, we discuss technologies that are available to measure optical properties of coccolithophores, and also how we could exploit coccolithophore optical properties to measure impacts of OA at different scales. We end with a discussion of the consequences (both optical and biogeochemical) of a “decalcified” surface ocean.

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