Sensitivity of coccolithophores to carbonate chemistry and ocean acidification

Abstract

About one-third of the carbon dioxide (CO(2)) released into the atmosphere as a result of human activity has been absorbed by the oceans, where it partitions into the constituent ions of carbonic acid. This leads to ocean acidification, one of the major threats to marine ecosystems and particularly to calcifying organisms such as corals, foraminifera and coccolithophores. Coccolithophores are abundant phytoplankton that are responsible for a large part of modern oceanic carbonate production. Culture experiments investigating the physiological response of coccolithophore calcification to increased CO(2) have yielded contradictory results between and even within species. Here we quantified the calcite mass of dominant coccolithophores in the present ocean and over the past forty thousand years, and found a marked pattern of decreasing calcification with increasing partial pressure of CO(2) and concomitant decreasing concentrations of CO(3)(2-). Our analyses revealed that differentially calcified species and morphotypes are distributed in the ocean according to carbonate chemistry. A substantial impact on the marine carbon cycle might be expected upon extrapolation of this correlation to predicted ocean acidification in the future. However, our discovery of a heavily calcified Emiliania huxleyi morphotype in modern waters with low pH highlights the complexity of assemblage-level responses to environmental forcing factors.

Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and p CO 2

“…calcium and inorganic carbon transport, H þ transport and carbonic anhydrases) have been identified via gene expression studies comparing calcifying and non-calcifying E. huxleyi cells [25][26][27][28][29], or in short-term experiments where calcification was regulated by limitation of ions needed for calcification (i.e. Ca 2þ , HCO 3 2 /CO 3 22 [26,30,31]). …”

“…When CO 2 dissolves in seawater, carbonic acid forms, lowering the pH and altering the absolute and relative abundances of dissolved carbonate species; this process is known as 'ocean acidification' (OA) [2]. OA affects photosynthesis and calcification of marine organisms such as coccolithophores [3][4][5], unicellular microalgae that surround themselves with scales of calcium carbonate (coccoliths). In turn, photosynthesis and calcification affect air-sea CO 2 exchange and carbon export to the deep sea [6].…”

Reconsidering the role of carbonate ion concentration in calcification by marine organisms

“…1) at the site of calcification does not have to be taken from the seawater CO 2− 3 pool but could equally well originate from the seawater CO 2 or HCO − 3 reservoir and be transformed to CO 2− 3 shortly before reacting with Ca 2+ . Despite the unknown seawater DIC source for CaCO 3 precipitation, or the CO 2− 3 -dependent CaCO 3 are often considered a priori as the key carbonate system parameters determining calcification rates or the fitness of calcifying organisms in the oceans (Kleypas et al, 1999;Beaufort et al, 2011). This assumption is reasonable under corrosive conditions (i.e., CaCO 3 < 1) where ] controls the dissolution of CaCO 3 (Eq.…”

Balancing of Ocean Acidification by Superoxide Redox Chemistry?

“…In warm, sunlit surface seawater the photochemical and biological processes that are involved in the degradation of DOM and POM can be strongly enhanced, leading to increased production of CO 2 and of anionic species that decrease the alkalinity of seawater. 2 The third possible issue is connected with atmospheric acid rain, most notably involving HNO 3 and H 2 SO 4 that can directly lower the seawater pH. 2 All such processes are usually limited to the coastal areas that are most affected by eutrophication phenomena, while acid rains are not expected to have a comparatively important impact on the pH of the open ocean.…”