Abstract
Temperature, light and carbonate chemistry speciation all influence the growth, calcification and photosynthetic carbon fixation rates of coccolithophores to a similar degree. There have been multiple attempts to project the responses of coccolithophores to changes in carbonate chemistry, but the interaction with light and temperature remains elusive. Here we devise a simple conceptual model to derive a fit equation for coccolithophorid growth, photosynthetic carbon fixation and calcification rates in response to simultaneous changes in carbonate chemistry speciation, temperature and light conditions. The fit equation is able to account for up to 88% of the variability in measured metabolic rates. Equation projections indicate that temperature, light and carbonate chemistry speciation all have different modulating effects on both optimal growth conditions and the sensitivity of responses to extreme environmental conditions. Calculations suggest that a single extreme environmental condition (CO2, temperature, light) will reduce maximum rates regardless of how optimal the other environmental conditions may be. Thus, while the response of coccolithophores to ocean change depends on multiple variables, the one which is least optimal will have the most impact on overall rates. Finally, responses to ocean change are usually reported in terms of cellular rates. However, changes in cellular rates can be a poor predictor for assessing changes in production at the community level. We therefore introduce a new metric, the calcium carbonate production potential (CCPP), which combines the independent effects of changes in growth rate and cellular calcium carbonate content to assess how environmental changes will impact coccolith production. Direct comparison of CO2 impacts on cellular CaCO3 production rates and CCPP shows that while the former is still at 45% of its pre-industrial capacity at 1000 uatm, the latter is reduced to 10%.
Highlights
Coccolithophores are an abundant, ubiquitous component of marine phytoplankton assemblages (McIntyre and Bé, 1967; Charalampopoulou, 2011; Okada and Honjo, unpublished manuscript)
Equation (8) with its coefficients was able to explain up to 88% of the variability in measured metabolic rates across a relatively broad range of carbonate chemistry (25–3,500 μatm), light (50–800 μmol photons m−2s−1) and temperature (15–25◦C) conditions
Equation (8) was able to describe the effects of substrate limitation and stimulation and hydrogen ion (H+) inhibition on metabolic rates (Figure 5)
Summary
Coccolithophores are an abundant, ubiquitous component of marine phytoplankton assemblages (McIntyre and Bé, 1967; Charalampopoulou, 2011; Okada and Honjo, unpublished manuscript). Coccolithophores have been influencing the Earth’s biogeochemical element cycling for over 200 million years (Ridgwell, 2005; de Vargas et al, 2007). These organisms can contribute up to 20% of the total carbon production (calcification plus photosynthesis) in some ecosystems (Poulton et al, 2007, 2010), and up to 50% to the calcium carbonate (CaCO3) content found in Holocene marine sediments (Broecker and Clark, 2009). It is hypothesized that DMSP production by coccolithophore blooms, in particular Emiliania huxleyi, may influence the Earth’s albedo (Holligan et al, 1993a). Changes in coccolithophore abundance and productivity have the potential to significantly impact both the marine and global carbon cycles (Zondervan et al, 2001; Riebesell et al, 2009)
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