Babette Boeckel

New insights into deformation and fluid flow processes in the Nankai Trough accretionary prism: Results of Ocean Drilling Program Leg 190

Moore, G. F., Taira, A., Klaus, A., Becker, L., Boeckel, B., Cragg, B. A., Dean, A., Fergusson, C. L., Henry, P., Hirano, S., Hisamitsu, T. et al. (2001). New insights into deformation and fluid flow processes in the Nankai Trough accretionary prism: Results of Ocean Drilling Program Leg 190. Geochemistry, Geophysics, Geosystems, 2, Article No: 2001GC000166.

Coccolith contribution to South Atlantic carbonate sedimentation

In order to assess the significance of calcifying organisms for the carbonate budget it is necessary to have reliable estimates of the relative proportion of carbonate production of the different organism groups. In this chapter we firstly review the carbonate distribution patterns of both bulk coccoliths and planktic foraminifera, estimated by means of different carbonate calculation techniques. These studies clearly reveal a variable pattern of carbonate sedimentation and accumulation for planktic foraminifera and coccolithophores, respectively. Whilst coccolith carbonate dominates the oligotrophic gyres of the South Atlantic, carbonate produced by planktic foraminifera is more important in more fertile, mesotrophic to eutrophic areas, such as the equatorial divergence zone. Mass estimates of coccolith carbonate burial in surface sediments of the South Atlantic document coccoliths to be major carbonate contributors in most mid-Atlantic Ridge sediments, exceeding up to 70 wt.-%. In contrast to these oligotrophic areas, they are of lesser importance in sediments accumulating on the continental margins, where they account for only a fifth of the carbonate fraction.

Seasonal productivity dynamics in the pelagic central Benguela System inferred from the flux of carbonate and silicate organisms

Flux of bulk components, carbonate- and silicate-bearing skeleton organisms, and the d 15 N-isotopic signal were investigated on a 1-year time-series sediment trap deployed at the pelagic NU mooring site (Namibia Upwelling, ca. 29jS, 13jE) in the central Benguela System. The flux of bulk components mostly shows bimodal seasonality with major peaks in austral summer and winter, and moderate to low export in austral fall and spring. The calcium carbonate fraction dominates the export of particulates throughout the year, followed by lithogenic and biogenic opal. Planktonic foraminifera and coccolithophorids are major components of the carbonate fraction, while diatoms clearly dominate the biogenic opal fraction. Bulk d 15 N isotopic composition of particulate matter is positively correlated with the total mass flux during summer and fall, while negatively correlated during winter and spring. Seasonal changes in the intensity of the main oceanographic processes affecting the NU site are inferred from variations in bulk component flux, and in the flux and diversity patterns of individual species or group of species. Influence from the Namaqua (Hondeklip) upwelling cell through offshore migration of chlorophyll filaments is stronger in summer, while the winter flux maximum seems to reflect mainly in situ production, with less influence from the coastal and shelf upwelling areas. On a yearly basis, dominant microorganisms correspond well with the flora and fauna of tropical/ subtropical waters, with minor contribution of near-shore organisms. The simultaneous occurrence of species with different ecological affinities mirrors the fact that the mooring site was located in a transitional region with large hydrographic variability over short-time intervals. D 2002 Elsevier Science B.V. All rights reserved.

Spatial distribution of living coccolithophores in the southwestern Gulf of Mexico

The present study was conducted to provide information about the upper water column distribution of living coccolithophores in the subtropical Gulf of Mexico. In total, 52 plankton samples from 6 stations collected in March 2006 were analysed. Coccolithophore standing crops range from zero in deep-water samples (200 m) to about 23 000 to 46 500 coccospheres per litre at intermediate water depths. From 39 identified taxa, only nine species contribute significant cell numbers of more than 1000 cells 1–1 and comprise more than 5 % of the communities in at least one sample. Emiliania huxleyi was the most abundant species throughout the stations with concentrations of up to 22 700 cells l–1. At all stations, a vertical succession of coccolithophore species was found. Umbellosphaera tenuis (type IV), Discosphaera tubifera, Rhabdosphaera clavigera and, as a minor component, species of the genus Syracosphaera, were mainly restricted to surface waters (≤50 m), all adapted to lower nutrient levels. The assemblage in the deep photic zone (50–150 m water depth) was composed mainly of abundant Florisphaera profunda, Gladiolithus flabellatus and Algirosphaera robusta indicating a tolerance of lower light availability. Thus, the vertical distribution of all coccolithophorid taxa, except the placolith-bearing species, in particular E. huxleyi, was probably controlled by upper photic-zone water temperature and stratification of the water column.