Genetic and Physiological Influences on the Alkenone/Alkenoate Versus Growth Temperature Relationship in Emiliania huxleyi and Gephyrocapsa Oceanica

Selected warm and cold water strains of the coccolithophorid Emiliania huxleyi and the closely related species Gephyrocapsa oceanica were cultured under controlled temperature conditions to assess genetic and physiological variability in the alkenone/alkenoate vs. temperature relationship. Differences in the strains’ growth rates over the 6–30°C experimental temperature range were small but consistent with their cold or warm water origins. E. huxleyi and G. oceanica had similar alkenone/alkenoate biochemistry, justifying the extension of alkenone stratigraphy to sediments predating the appearance of E. huxleyi. These species could not be distinguished by C 38 /C 37 alkenone or alkenoate/alkenone ratios as previously suggested ( Volkman et al. 1995 ; Sawada et al. 1996 ) but given samples from a range of temperatures may be distinguished by a plot of the C 38 ethyl vs. C 38 methyl unsaturation ratios (U 38Et K and U 38Me K, respectively).