Showing papers by "Wolfgang H Berger published in 1998"

Silica depletion in the thermocline of the glacial North Pacific: corollaries and implications

Abstract: Over much of the tropical ocean, late Quaternary productivity patterns show maxima associated with glacial periods, minima during warm times. Also, biogenic opal deposition tends to parallel the accumulation rates of organic carbon and related productivity proxies. This pattern is found in the eastern equatorial Pacific, for example. However, in the western equatorial Pacific, while productivity is normally high during glacials, opal deposition is reduced. In Santa Barbara Basin, both organic matter supply and opal supply are reduced during the last glacial period, showing a reversed productivity pattern. Silicate/phosphate ratios at 100 m depth in Pacific waters and elsewhere suggest that present circulation greatly favors silicate enrichment of the thermocline in the North Pacific, presumably through large-scale deep upwelling, which prevents segregation of silicate from phosphate through partial recycling in the uppermost water column. If so, it appears that the opal supply to Santa Barbara Basin may indicate the nutrient content of the North Pacific thermocline. We suggest that during the last glacial period the nutrient content of the thermocline was low, and large-scale deep upwelling was absent. The records of organic matter supply and laminations show patterns that call for additional factors, presumably changing wind strength, changing shelf exposure, and local feedback effects.

Ocean drilling program leg 175 preliminary report benguela current

Abstract: This informal report was prepared from the shipboard files by the scientists who participated in the cruise. The report was assembled under time constraints and is not considered to be a formal publication which incorporates final works or conclusions of the participating scientists. The material contained herein is privileged proprietary information and cannot be used for publication or quotation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the participating agencies, ABSTRACT During Leg 175, thirteen sites were occupied off the western coast of Africa (Congo, Angola, Namibia, and South Africa), and 40 holes were drilled using advanced hydraulic piston coring and the extended core barrel method. The goal is to reconstruct the late Neogene history of the Benguela Current and the associated upwelling regimes between 5° and 32°S. The area investigated contains one of the greatest upwelling regions of the world, intermediate in intensity between the systems off Peru and California. The Angola-Benguela Current system with its associated upwelling regions ("ABC-system") is characterized by organic-rich sediments that contain an outstanding record of productivity history, which can be read on a very fine scale. In addition, this environment provides an excellent setting for natural experiments in diagenesis. The individual transects selected for drilling within the ABC-system reflect a compromise among geographic coverage, accessibility, quality of sedimentary record, and time constraints. Variations in productivity are generated in different ways, within different geographic settings (off the Congo, near the Angola Dome, at Walvis Ridge, in the upwelling cells south of the ridge). One of the major goals is to document fluctuations in productivity in these different settings in relationship to large-scale climate change within the late Neogene, including the onset of glacial cycles in the Northern Hemisphere. Another major goal is to tie the fluctuations in oceanic conditions to the corresponding changes in climate on the adjacent continent. Most of the sites drilled have high sedimentation rates (ca. 100 m/m.y.), which offers an opportunity to develop detailed paleoceanographic records, with a resolution near 1000 yr. Sediments are largely diatomaceous and carbonate-rich clays with variable (and occasionally very high) organic carbon contents. Analysis of these sediments will greatly extend and refine results concerning paleoceanography and paleoclimate of the late Neogene that were provided by Deep Sea Drilling Project Sites 362 and 532. contain the …