LONG-CHAIN ALKENONES AND ALKYL ALKENOATES IN THE COASTAL AND PELAGIC SEDIMENTS OF THE NORTHWEST NORTH PACIFIC, WITH SPECIAL REFERENCE TO THE RECONSTRUCTION OF EMILIANIA-HUXLEYI AND GEPHYROCAPSA-OCEANICA RATIOS

Long-chain (n C-37-C-39) alkenones and (n C-37-C-38) alkyl alkenoates in marine sediments are derived mainly from two marine coccolithophori ds, Emiliania huxleyi and Gephyrocapsa oceanica. Laboratory cultured s trains of E. huxleyi (strain EH2) and G. oceanica (strain GO1), isolat ed from the Great Barrier Reef and Mutsu Bay in northern Japan (41 deg rees N, 141 degrees E), respectively, were cultured at 10 degrees C, 1 5 degrees C, 20 degrees C, 22 degrees C, 25 degrees C, 28 degrees C an d analyzed for C-37 to C-39 alkenones, C-36 methyl alkenoate (FAME) an d C-36 ethyl alkenoate (FAEE). Results obtained indicated significant differences in the alkenone and alkyl alkenoate profiles between these two algal species. The ratios of FAEE to C-37 alkenones (EE/K37) and C-38 alkenones (EE/K38) in G. oceanica were higher than those ill E. h uxleyi and, for both algal species, these ratios showed strong negativ e nonlinear exponential correlations when plotted against the unsatura tion index of C-37 alkenones (U-37(k)). Using fitted equations for the se relationships, the relative abundance of E. huxleyi and G. oceanica in the sediment samples from the northwest North Pacific and the coas tal and inland waters of Japan were estimated and compared with direct microscopic determinations. E. huxleyi comprised more than 80% of the sedimentary coccolith assemblage in the open ocean, whereas G. oceani ca was exclusively dominant in the inland waters. These results almost agreed with microscopic counts of these coccoliths occurring in the s ediment samples. In the light of these findings, we suggest that there is a possibility that the relative abundance of E. huxleyi and G. oce anica in sediments may be estimated using nonlinear exponential calibr ations based on EE/K37 to U-37(k) and EE/K38 to U-37(k) regressions. C opyright (C) 1996 Elsevier Science Ltd