Comparison of living and surface sediment coccolithophore assemblages in the Pacific sector of the Southern Ocean

This study examined recent coccolith surface sediment assemblages across the Pacific sector of the Southern Ocean (from Punta Arenas, Chile to Wellington, New Zealand). Twenty five stations located within 44.4°S to 65.4°S and 80.1°W to 174.5°E were selected in order to assess if and how the surface sediment assemblages reflect the present-day coccolithophore community and surface-water océanographie conditions. The highest numbers of coccoliths in the surface sediments are reached near the East Pacific Rise and close to the Subtropical Front, at the New Zealand Margin (>6×10⁹ coccoliths/g of sediment). The dominant taxa are Emiliania huxleyi (including types A, B, B/C and C), Calcidiscus leptoporus, Gephyrocapsa spp. (including G muellerae, G oceanica and G ericsonii), Umbellosphaera tenuis and Coccolithus braarudii. Despite the recognition of species morphotypes being hampered by carbonate dissolution at some locations, we observed that numbers generally decrease southward until almost a monospecific and sporadic record of E. huxleyi (types B/C and C) and C. leptoporus south of the Polar Front occurs. The recent coccolithophore distribution was compared to already published living coccolithophore distributions (i.e., water column samples collected at the same specific locations) showing a fairly similar pattern. Combining the numbers of cells/1 and coccoliths/g of sediment, different coccolithophore assemblages were established coincident with areas bounded by the major surface océanographie fronts, i.e. the Subantarctic Zone and the Polar Front Zone.