Control of ambient pH on growth and stable isotopes in phytoplanktonic calcifying algae

Abstract

The present work examines the relationship between pH-induced changes in growth and stable isotopic composition of coccolith calcite in two coccolithophore species with a geological perspective. These species (Gephyrocapsa oceanica and Coccolithus pelagicus) with differing physiologies and vital effects possess a growth optimum corresponding to average pH of surface seawater in the geological period during their first known occurrence. The "ancestral" C. pelagicus has much wider pH tolerance in terms of growth rates than the more recently evolved G. oceanica. Diminished growth rates are explained by the challenge of proton translocation into the extracellular environment at low pH and enhanced aqueous CO 2 limitation at high pH. Reducing the cell dynamics in this way leads to a lower degree of oxygen isotopic disequilibrium in G. oceanica. In contrast, the slower growing species C. pelagicus, which typically precipitates near-equilibrium calcite, does not show any modulation of oxygen isotope signals with changing pH. Overall, carbon and oxygen isotope compositions are best explained by the degree of utilization of the internal dissolved inorganic carbon (DIC) pool and the dynamics of isotopic reequilibration inside the cell. Thus, the "carbonate ion effect" may not apply to coccolithophores. This difference with foraminifera can be traced to different modes of DIC incorporation into these two distinct biomineralizing organisms. From a geological perspective, these findings have implications for refining the use of oxygen isotopes to infer more reliable sea surface temperatures (SSTs) from fossil carbonates and contribute to a better understanding of how climate-relevant parameters are recorded in the sedimentary archive.

Environmental controls on the growth, photosynthetic and calcification rates of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi

“…Specifically, due to the presence of a H 1 permeable pathway located on the E. huxleyi plasma membrane, the intracellular pH of E. huxleyi may decrease linearly with decreasing extracellular pH and increasing HCO 2 3 concentration in the medium (Suffrian et al 2011), i.e., increasing pCO 2 in our study. Therefore, intracellular acidification may require more energy to counteract cytosol acidification by neutralizing the H 1 generated from calcification (Nimer and Merrett 1993;Hermoso 2015), leading to the decreased calcification observed in the present study, especially at the highest pCO 2 .…”

Assessing ocean alkalinity for carbon sequestration

“…In these experiments there was little change in particulate inorganic carbon production (for Gephyrocapsa oceanica and C. pelagicus at pCO 2 = 1 800 ppmv, and Ω calcite = 13), whereas variations in organic carbon fixation were detected. However, Hermoso [] demonstrated a parabolic relationship between pH (and Ω) and growth rate for the same species. The results in Bach et al [] for Emiliania huxleyi are highly relevant to ocean alkalinity addition.…”

“…For instance, Barker and Elderfield [2002] ]), which Figure 10. Indicative Ω calcite ranges of culture experiments investigating calcification rate [Bach et al, 2011;Broecker et al, 2001;Comeau et al, 2009;Gattuso et al, 1998;Hermoso, 2015;Hoppe et al, 2011;Iglesias-Rodriguez et al, 2008;Langdon et al, 2000;Langdon and Atkinson, 2005;Langer et al, 2006;Leclercq et al, 2000;Maier et al, 2011;Rickaby et al, 2010;Ries et al, 2009;Rokitta et al, 2012].…”

Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

“…In sequences postdating the Late Miocene, large isotope vital effects have been reported in coccoliths (21). This was attributed to the consequence of relatively low pCO 2 concentrations, as DIC/CO 2 aq limitation is thought to be the main cause of the vital effects in these biominerals (20,21,(23)(24)(25)(26)(27). In contrast, studies of laboratory cultures and downcore sediments indicate that the vital effect in coccoliths (regardless of taxonomy) was limited and invariant when pCO 2 concentrations in the atmosphere were above ∼500 ppm, as was the case during the time period investigated (28, 29) (see SI Materials and Methods for further explanations on the relation…”