Controls on shell thickness in modern planktonic foraminifera

Abstract:

Planktonic foraminifera calcification response to ocean acidification can be studied using shell parameters such as shell size, mass and thickness (derived from shell area density). Shell thickness changes in planktonic foraminifera have previously been linked to variations in carbonate ion concentration, light intensity, temperature and nutrient availability, providing a proxy for past changes in seawater properties. While culture studies are invaluable in assessing the main controls on shell calcification in certain species, open ocean studies are needed to understand the impact of multi-stressor environments on shell parameters of multiple species and their potential as palaeo-proxies.

In this study, we present data on shell thickness of four depth-stratified species of modern planktonic foraminifera (Globoratalia truncatulinoides, Globoratalia inflata, Orbulina universa, Globigerinoides ruber-pink) from bi-weekly time-series sediment trap samples in the Sargasso Sea (Ocean Flux Program). We also use species flux, geochemical data and measured hydrographic data from Bermuda Atlantic time series to understand the seasonal and interannual changes in shell thickness due to changes in seawater properties.

We show that short-lived environmental perturbations such as cyclonic eddies affect local hydrographic conditions and can dramatically influence species fluxes and shell thicknesses. Our results suggest that a combined morphometric and geochemical approach to fossil planktonic foraminifera would allow a better understanding of calcification response to past environmental change.