Sodium and potassium analysis of individual coccoliths by secondary ion mass spectrometry

Abstract

Coccoliths are individual plates of calcium carbonate that comprise the shells of marine calcifying haptophyte algae. Their remains provide an excellent sedimentary archive for the reconstruction of past environmental parameters. Using nano-scale secondary ion mass spectrometry (NanoSIMS), we measured the Mg, Sr, Na and K contents in individual coccoliths of Emiliania huxleyi, now named Gephyrocapsa huxleyi, to explore their potential as a paleoproxy. For recent environmental samples from the Mediterranean and Black Sea as well as cultured specimens, all elements appeared to be homogeneously distributed within, but highly variable among, the individual coccoliths. Mg/Ca and Sr/Ca ratios covered a range of 0.06–83 mmol mol⁻¹ and 1.9–3.8 mmol mol⁻¹, respectively, and were in line with the previously determined values. Na/Ca ranged between 1.6–186 mmol mol⁻¹. K/Ca could not be calibrated, but the measured ³⁹K⁺/⁴⁴Ca⁺ ion count ratios varied between 0.03–2.7. Although the Na/Ca ratios significantly decreased with increasing total alkalinity and salinity in the Mediterranean samples, these trends were not observed in samples collected from cultures where the alkalinity and salinity varied separately. Similarly, K/Ca ratios showed no clear trends with total alkalinity or salinity of the culture medium. Calcification in coccolithophores is biologically controlled and this may mask the impact of environmental factors on the observed variation in the Na and K content of individual coccoliths of E. huxleyi.