Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

Michael J Henehan,Gavin L Foster,Janet E Burke,Eleni Anagnostou,Madison Shankle,Claudia H S Alt,Joseph A Stewart,David Evans,Pincelli M Hull,Joseph Durrant,Thomas B Chalk

doi:10.5194/bg-14-3287-2017

Abstract

Abstract. The response of the marine carbon cycle to changes in atmospheric CO2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification in these organisms to environmental change is critical. Despite this, there remains little consensus as to whether, or to what extent, chemical and physical factors affect foraminiferal calcification. To address this, we directly test the effect of multiple controls on calcification in culture experiments and core-top measurements of Globigerinoides ruber. We find that two factors, body size and the carbonate system, strongly influence calcification intensity in life, but that exposure to corrosive bottom waters can overprint this signal post mortem. Using a simple model for the addition of calcite through ontogeny, we show that variable body size between and within datasets could complicate studies that examine environmental controls on foraminiferal shell weight. In addition, we suggest that size could ultimately play a role in determining whether calcification will increase or decrease with acidification. Our models highlight that knowledge of the specific morphological and physiological mechanisms driving ontogenetic change in calcification in different species will be critical in predicting the response of foraminiferal calcification to future change in atmospheric pCO2.

Highlights

Calcium carbonate (CaCO3) production and transport to the deep ocean is one of the most important sinks of carbon, acting across a range of geological timescales (Sigman et al, 2010; Berner and Raiswell, 1983)
We have developed a new metric, calcification intensity (CI; Eq 2), that accounts for both the size/mass of foraminifera upon collection, as well as the amount of mass added between culture experiments: mass area where mass is the difference in mass between the start and end of the culture and area is the difference in product of the major and minor axes between the start and end of the culture
From the perspective of foraminiferal cultures, these models predict a strong dependency of CI on foraminifer size on collection, and the number of chambers precipitated in culture

Summary

Introduction

Calcium carbonate (CaCO3) production and transport to the deep ocean (the so-called “carbonate pump”) is one of the most important sinks of carbon, acting across a range of geological timescales (Sigman et al, 2010; Berner and Raiswell, 1983). In the Cenozoic (0–66 Ma), biogenic CaCO3 production by foraminifera, coccolithophores and coral reef ecosystems comprises the vast majority of marine carbonate production (Ridgwell and Zeebe, 2005). The strength of this carbonate pump can be altered in three principal ways: (1) by changing the efficiency of inorganic and/or organic carbon export and burial, (2) by changing the absolute or relative abundance of calcifying and non-calcifying taxa, and (3) by changes in the calcification efficiency of marine calcifiers. All three factors are thought to be sensitive to environmental conditions Henehan et al.: Size-dependent response of calcification to acidification ence the extent to which foraminifera calcify their tests (i.e. their “calcification intensity”)

Methods

Results

Discussion

Conclusion