A deep-sea core from the eastern equatorial Atlantic (Meteor core 16772, 1 degrees 21'S, 11 degrees 58'W) revealed strong primary productivity variations (70-230 gC/m (super 2) /year) based on the relative abundance (%) of the deep living coccolithophore Florisphaera profunda with productivity maxima following temperature minima during the last 200,000 years. The response of the coccolithophore flora was investigated by relative and absolute abundance records of coccoliths. The wind strength and the resulting equatorial upwelling intensity are thought to comprise the most important control of coccolith abundance and species composition, which reflects the different abundance of coccolithophores living in the upper or lower photic zone. Relative abundances of the different species varies widely throughout the core. Although a wide range of species were present in the different samples, three different taxa dominated the assemblage. The lower photic zone species F. profunda was the most abundant, with a mean relative abundance of 49.4% throughout the core. The upper photic zone flora were divided into three groups. Emiliania huxleyi together with small Gephyrocapsa (<3mu m) was the second most abundant species group (mean 20.8%). Gephyrocapsa oceanica was the third most important species in the core and had a mean relative abundance of 16.8%. All other species together represented a mean of 13%. Highest absolute abundance of coccoliths (number/gram sediment) occurs in sediments deposited during periods of high SST, mainly in warm isotope stages 1 and 5. The accumulation rates of coccoliths (number/cm (super 2) /ky) show peaks in isotope stages 1 and 5, but also in some parts of cool isotope stages 4 and 6. High relative and absolute abundance of F. profunda were found in warm isotope stages, which suggests that a deep nutricline existed and that primary productivity was low. Absolute and relative abundance records of E. huxleyi and small Gephyrocapsa (<3mu m) mainly showed higher values in sediments from warm periods. The other upper photic zone coccolith species were generally more abundant during periods of low SST, particularly in isotope stages 2, 4, and 6, which were times of high primary productivity and a shallow nutricline. This suggest that E. huxleyi and small Gephyrocapsa probably were able to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone. In summary, the composition of the coccolith flora can be explained by the nutricline depth level with three different assemblages being recognized, a deep photic zone assemblage consisting of F. profunda, a middle-upper photic zone assemblage of E. huxleyi and small Gephyrocapsa and an upper photic zone assemblage consisting of all other species.

Dimethylsulfide (DMS) released from phytoplankton produces cloud condensation nuclei in the marine troposphere, thereby providing a climate-regulating mechanism by increasing cloud albedo. A 200-k.y.-long sedimentary record from the equatorial Atlantic of DMS-producing phytoplankton suggests that DMS production increased during the glacial stages, thus potentially working to further cool the glacial world. Important factors limiting the operation of this possible feedback mechanism for planetary cooling may be the strength of trade winds and the availability of fine, iron-rich dust needed to fertilize growth of DMS producers.

The global extinctions linked to the Cretaceous-Tertiary (K-T) boundary severely affected marine pelagic organisms. The K-T boundary intervals at Deep Sea Drilling Project (DSDP) Site 527 (Leg 74) in the South Atlantic Ocean and Site 465 (Leg 62) in the Pacific Ocean were studied for changes in calcareous nannofossil assemblages from the late Maastrichtian to the early Paleocene. The sections analysed cover 180 kyr of the terminal Cretaceous and 200 kyr of the earliest Tertiary. Absolute and relative abundances of calcareous nannoplankton were calculated for both the entire flora and for individual species. No decrease in the number of species occurs towards the K-T boundary; relative and absolute abundances of different species are fairly stable throughout the terminal 180 kyr of the Cretaceous. At the K-T boundary the calcareous nannoflora shows a drastic and instantaneous decrease in absolute abundance. Typical Cretaceous species became extinct at the K-T boundary, but are present in the lowermost Tertiary as a result of bioturbation and reworking of the sediments. Very few species survived the K-T boundary. The species that occur sporadically in extremely low numbers in the Cretaceous, exhibit stable relative and absolute abundances through the lower Tertiary. Evolving Tertiary species appeared at the boundary and vary only moderately in absolute abundance through the lowermost Paleocene. The productivity of calcareous nannoplankton is determined here as the nannofossil accumulation rate (NFAR), which is suggested as an estimate of surface-water primary productivity. The terminal Cretaceous NFAR values were high and stable. At the K-T boundary the calcareous nannoflora suffered a 70-150-fold decrease in NFAR, indicating a catastrophic event. The Tertiary NFAR values remained low and fairly constant through the first 200 kyr. The productivity of calcareous nanno- plankton in the earliest Tertiary was dominated by the calcareous dinoflagellateThoracosphaerasp.

Seven Deep Sea Drilling Project (DSDP) sites, were examined in order to determine the chronology of the late Maastrichtian calcareous nannofossil Micula prinsii Zone. Six sites span the terminal Cretaceous palaeolatitudinal interval between 36°S and 37°N in the Atlantic ocean, and one site was from a palaeolatitude of 16°N in the Pacific Ocean. The M. prinsii Zone is often used to demonstrate the presence of terminal Cretaceous sediments. The chronology of the M. prinsii Zone is based on abundance counts and the base of this zone is correlated to the magnetic polarity stratigraphy. Micula prinsii first appeared near the base of subchron C29R. The estimated first appearance of M. prinsii is 0.25 ± 0.02 m.y. before the Cretaceous-Tertiary (K-T) boundary in the South Atlantic, 0.22 ± 0.02 m.y. before the K-T boundary in the North Atlantic and 0.19 ± 0.01 m.y. before the K-T boundary in the North Pacific. The M. prinsii Zone extends up to the K-T boundary, where its index species is among the Cretaceous calcareous nannofossil stock that became extinct. This zone is an important tool for verification of the completeness of terminal Maastrichtian sequences from low to middle latitudes.