A data–model synthesis to explain variability in calcification observed during a CO<sub>2</sub> perturbation mesocosm experiment

Abstract

Abstract. The effect of ocean acidification on growth and calcification of the marine algae Emiliania huxleyi was investigated in a series of mesocosm experiments where enclosed water volumes that comprised a natural plankton community were exposed to different carbon dioxide (CO 2 ) concentrations. Calcification rates observed during those experiments were found to be highly variable, even among replicate mesocosms that were subject to similar CO 2 perturbations. Here, data from an ocean acidification mesocosm experiment are reanalysed with an optimality-based dynamical plankton model. According to our model approach, cellular calcite formation is sensitive to variations in CO 2 at the organism level. We investigate the temporal changes and variability in observations, with a focus on resolving observed differences in total alkalinity and particulate inorganic carbon (PIC). We explore how much of the variability in the data can be explained by variations of the initial conditions and by the level of CO 2 perturbation. Nine mesocosms of one experiment were sorted into three groups of high, medium, and low calcification rates and analysed separately. The spread of the three optimised ensemble model solutions captures most of the observed variability. Our results show that small variations in initial abundance of coccolithophores and the prevailing physiological acclimation states generate differences in calcification that are larger than those induced by ocean acidification. Accordingly, large deviations between optimal mass flux estimates of carbon and of nitrogen are identified even between mesocosms that were subject to similar ocean acidification conditions. With our model-based data analysis we document how an ocean acidification response signal in calcification can be disentangled from the observed variability in PIC.

Upwelled plankton community modulates surface bloom succession and nutrient availability in a natural plankton assemblage

“…Natural variability in composition or fitness in initial plankton assemblages can bring about significant variability in measured response variables that can be larger than those driven by the treatment itself (Krishna and Schartau (2017)). Yet it is surprising for such a strong driver of phytoplankton succession, like nitrate concentrations, that the deep water biology had such a measurable influence.…”

Upwelled plankton community modulates surface bloom succession and nutrient availability in a natural plankton assemblage

“…Natural variability in composition or fitness in initial plankton assemblages can bring about significant variability in measured response variables that can be larger than those driven by the experimental treatment itself (Krishna and Schartau, 2017). Yet it is surprising for such a strong driver of phytoplankton succession, like nitrate concentrations, that the deep water biology had such a measurable influence.…”

Reanalysis of vertical mixing in mesocosm experiments: PeECE III and KOSMOS 2013

“…Therefore, they provide unique insights into possible responses of planktonic ecosystems to anthropogenic pressures that cannot be obtained from laboratory studies. Past mesocosm experiments investigated, for example, the effects of decreasing pH (Riebesell et al, 2008(Riebesell et al, , 2013Gazeau et al, 2016;Engel et al, 2014;Galgani et al, 2014;Archer et al, 2018), nutrient increase (Schwier et al, 2017;Micheli, 1999), and warming (Lewandowska et al, 2014;Sommer et al, 2015;Wohlers et al, 2009). Ocean acidification has been found to have a significant impact on organic matter stoichiometry (Riebesell et al, 2007;Schulz et al, 2008), plankton community composition (Bach et al, 2016;Riebesell et al, 2017;Boxhammer et al, 2018), primary production, and carbon export (Egge et al, 2009;Riebesell et al, 2007).…”