Optimum growth conditions as opposed to calcite saturation as a control on the calcification rate and shell-weight of marine foraminifera

Processes that impact negatively on CaCO3 production and calcification rates, such as a lowering of the carbonate saturation state of the surface ocean in response to higher atmospheric CO2 levels, can have disastrous consequences for marine ecosystems. This study, however, shows that on a global basis planktonic foraminiferal calcification rates (as inferred from shell-weight) are not related to calcite saturation state, as has been inferred from culture experiments and across a short latitudinal core-top transect. Rather, foraminiferal calcification is apparently a function of the same complex interplay of environmental parameters as assemblage abundance patterns. Highest foraminiferal shell-weights are observed within the optimum ecological niche of each planktonic species and no simple relationship with calcite saturation, temperature or surface nutrient levels exists. The implications of calcification-saturation relationships in calcifying marine ecosystems should therefore be evaluated in a broader context than has been the case in recent studies.