The absolute abundance of calcareous nannofossils ranged from 3.0 × 107 to 46.4 × 107 individuals per gram of sediment, with an average value of 12.3 × 107 individuals per gram of sediment (Fig. 1). Higher abundances of calcareous nannofossils were observed at 20-17 ka, 15-12 ka, and 11-6.5 ka, whereas the lower values occurred at 23-21 ka and 6-0 ka. Sharp peaks of nannofossil abundance were observed at 10 ka during Termination IB after the Younger Dryas cooling event (Fig. 1).
The coccolith assemblage during the last 27 k.y. was dominated by Gephyrocapsa muellerae, Florisphaera profunda, Emiliania huxleyi, Gephyrocapsa spp. (small size), and Gephyrocapsa oceanica (Table 1).
G. muellerae, regarded to prefer cool surface-water conditions (Samtleben et al., 1995), was highest in abundance between 22 and 16 ka, reaching 70% of the total coccolith assemblages (Fig. 2). The second abundance peak of this species was observed between 12 and 9 ka, followed by a gradual decrease towards the Holocene. Weaver and Pujol (1998) have reported that the abundance of G. muellerae increased in cold episodes before Termination IA and IB in the Alboran Sea. In Hole 1017E, G. muellerae has maxima values in the last glacial maximum and in the Younger Dryas.
F. profunda, generally abundant in the lower photic zone of tropical to temperate regions with a temperature range of 10°-28°C (Okada and McIntyre, 1979), increased in abundance during relatively warm intervals (Fig. 2). The peak values of this species were observed from 16 to 10.5 ka and 6 to 1 ka, and became rare between 18 and 17 ka and at 9 ka.
Highest abundance of Gephyrocapsa spp. (small size) occurred between 9 and 6 ka after Termination IB. The dominance of small Gephyrocapsa together with E. huxleyi are associated with periods of higher primary productivity or upwelling (Okada and Wells, 1997; Lototskaya et al., 1998). In Hole 1017E, therefore, it is presumed that upwelling took place during 9-6 ka.
A sharp increase in G. oceanica, which is generally abundant along ocean margins and in warm regions, was observed at 15.5 ka. E. huxleyi was abundant to common throughout the studied period but did not show a clear trend. Coccolithus pelagicus, which inhabits the cold water region, had a high peak between 24 and 23 ka and was diminished after 23 ka. Calcidiscus leptoporus and Helicosphaera carteri gradually increased their abundances toward the Holocene from 15 ka. Umbellosphaera irregularis, resident of warm surface waters, was present sporadically after ~18 ka (Samples 167-1017E-1H-1, 0-3 cm, through 1H-3, 54-57 cm) and scarcely between 27 and 18 ka (Samples 167-1017E-1H-3, 60-63 cm, through 1H-CC, 18-21 cm).
Species diversity expressed in Shannon-Weaver's information function varied between 1.1 and 2.2 (Fig. 3). The lowest value was recorded at 18 ka, and the higher values were observed between 15 and 0 ka. Generally, the species diversity increases when the abundance of G. muellerae decreased (correlation coefficient R2 = 0.78).