Technical note: A comparison of methods for estimating coccolith mass

Abstract

Abstract. The fossil record of coccolithophores dates back approximately 225 million years and the production of their calcite platelets (coccoliths) contributes to the global carbon cycle over short and geological time scales. Variations in coccolithophore parameters (e.g., community composition, morphology, size and coccolith mass) have been used as paleoproxy to understand past oceanographic conditions. Coccolith mass has been frequently estimated with different methods with electron microscopy the most applied. Here, we compared the electron microscopy (EM) method with the Coulter Multisizer (CM) (i.e., electric field disturbance) and Bidirectional Circular Polarization (BCP) methods to estimate coccolith masses in controlled laboratory experiments with two ecotypes of Emiliania huxleyi. Average coccolith mass estimates were in good agreement with literature data. However, mass estimates from CM were slightly overestimated compared to EM and BCP estimates and a correction factor (cf = 0.8) is suggested to compensate for this discrepancy. The relative change in coccolith mass triggered by morphotype specific structures and environmental parameters (i.e., seawater carbonate chemistry) was suitably captured by each of the three techniques.