Calcification in the planktonic foraminifera Globigerina bulloides linked to phosphate concentrations in surface waters of the North Atlantic Ocean

Abstract

Abstract. Marine calcifiers, such as planktonic foraminifera, form a major component of the global carbon cycle, acting as both a source and sink of CO2. Understanding factors that affect calcification in these organisms is therefore critical in predicting how the oceans will respond to increased CO2 concentrations in the atmosphere. Here, size-normalised weights (SNWs) of the planktonic foraminifera Globigerina bulloides, collected from the surface waters of the North Atlantic, are compared with in situ carbonate ion concentrations ([CO32−]), optimum growth conditions (implied from G. bulloides abundances), and nutrient concentrations. Significant positive relationships suggest that phosphate concentration ([PO43−]) has the greatest effect on G. bulloides SNWs, with reduced test masses at higher concentrations (range: 0.04–0.31 μM). [CO32−] appears to have a minor effect over the range of values examined (148–181 μmol kg−1), and no evidence was found for increased SNWs under apparent optimum growth conditions. These findings point to the potential importance of phosphate concentration in determining calcification rates in foraminifera, a factor which has been overlooked by previous studies on these organisms. The confirmation of these results via carefully controlled culture studies is recommended in the future.