Papers by Babette Boeckel
The present study was conducted to provide information about the upper water column distribution ... more 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 deepwater 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.
Micropaleontology
The scanning ElectronMicroscope (SEM) and the PetrographicMicroscope (Light Microscope, LM) are d... more The scanning ElectronMicroscope (SEM) and the PetrographicMicroscope (Light Microscope, LM) are devices which both are used in routine analysis of coccolithophore assemblages, but comparisons and/or combinations of quantitative data from both sources are difficult. In this paper a comparison is made between the results obtainedwith the Flores and Sierro settling technique (1997) for LMand the Andruleit filtration technique (1996) for SEM, considering their advantages and drawbacks. Twenty-six surface sediment samples from the SouthAtlantic and Southeast Pacificwere studied.All the taxa distinguished were reduced to fourteen groups accounting for 100%. The biogeographical patterns of coccolithophorid species and species groups determined using both techniques are highly comparable, although the trends in relative and absolute numbers are not always identical. In particular, the numbers of coccoliths per gram of sediment are higher in the case of the filtration technique/SEM-technique...
Flux of bulk components, carbonate- and silicate-bearing skeleton organisms, and the d15N-isotopi... more Flux of bulk components, carbonate- and silicate-bearing skeleton organisms, and the d15N-isotopic signal were investigated on a 1-year time-series sediment trap deployed at the pelagic NU mooring site (Namibia Upwelling, ca. 29°S, 13°E) 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 d15N 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.
ODP Preliminary Report, 2000
Ocean Drilling Program Legs 190 and 196 were a two-part program to study deformation and fluid fl... more Ocean Drilling Program Legs 190 and 196 were a two-part program to study deformation and fluid flow in the central Nankai Trough off Shikoku Island. During Leg 190 two reference sites were drilled outboard of the trench (Sites 1173 and 1178), one site into the protothrust zone (Site 1174), two sites into a trench slope basin above a major outof-sequence thrust (Sites 1175, 1176), and one site into an older portion of the accretionary prism. During Leg 196, Sites 1173 and 808 (drilled through the frontal thrust during Leg 131) were revisited, employing logging while drilling and installing two Advanced Circulation Obviation Retrofit Kits (ACORKs). Our reference sites defined the stratigraphic framework and physical properties baseline of the accreting/ subducting Shikoku Basin sedimentary section. The proto-thrust and frontal thrust sites documented the dewatering and deformation processes at the toe of the accretionary prism. Porosity comparisons between Sites 1173 and 808 suggest that elevated fluid pressures occur beneath the décollement at Site 808. Initial measurements from the ACORK at Site 808 indicate a pressure pulse apparently from the décollement. Negative chloride anomalies at Sites 1174 and 808 could be due to fluid flow from deeper in the prism, but active smectite dehydration could also be responsible for the anomalies. Resistivity imaging of the frontal thrust shows borehole breakouts with principal stress orientations consistent with core-scale structures and plate convergence
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Papers by Babette Boeckel