Showing papers by "Wolfgang H Berger published in 1992"

Reading the Sedimentary Record of the Ocean’s Productivity

Abstract: The basic controls on ocean productivity are poorly understood both biologically and geologically. In fact, we do not know the global patterns of productivity very well, either with regard to the rates of primary production (that is, the amount of carbon fixed in the photic zone each year), or with regard to the types of primary production (that is, the kinds of organisms involved).

Evidence for a bathyal front at 2000‐M depth in the glacial Pacific, based on a depth transect on Ontong Java Plateau

Abstract: Data on oxygen and carbon isotope compositions of the benthic foraminifer Planulina wullerstorfi from 18 cores (17 box cores and one piston core) from Ontong Java Plateau provide proxy depth profiles for temperature, water mass, and nutrient content for the late Holocene, the last transition, and the last glacial. The δ18O profile during glacial time shows an increased gradient at a depth near 2000 m. The corresponding δ13C data suggest that a bathyal nutricline existed close to the same depth level. The δ13C values provide limits on the global change in carbon content of the glacial ocean, which may be estimated as distinctly less than 1 atmospheric carbon mass (1 ACM = 700 GtC). The greater CO2 content of glacial deep waters, which is reflected in the more negative δ13C values, may be at least in part due to a more sluggish renewal of (abyssal) deep waters. If so, the water of the deep Pacific was up to 400 years older than now. In turn, ventilation in the upper waters, above 2000 m, may have been more vigorous than today.

Neues vom Ontong-Java-Plateau (Westpazifik)

Abstract: For the investigation of climatic history for the last 65 million years, several holes were drilled in 1990 on the Ontong Java Plateau by the drilling vessel Joides Resolution, under the auspices of the international Ocean Drilling Program. The Ontong Java Plateau is the largest basalt plateau on earth, and was formed in the Middle Cretaceous. From the core material, seismic reflectors from the overlying sediments can be associated with specific, climate-related oceanic events. For the cyclic sediments of the last 2 million years, high-resolution isotope curves were generated which depict the two dominant Milankovitch cycles with periods of 100 000 and 41000 years.

The record of Ontong Java Plateau: Main results of ODP Leg 130

Abstract: The drilling campaign of ODP Leg 130 on Ontong Java Plateau resulted in the recovery of complete Neogene sections at several depths, providing materials for detailed biostratigraphic and paleoceanographic studies in the western equatorial Pacific. The acquisition of extensive logging records and high-resolution physical-property data allow detailed correlation from hole to hole and from site to site and provide the basis for a paleoceanographic interpretation of acoustic reflectors. We drilled 16 holes at 5 sites on the north-eastern flank of the plateau (Sites 803 through 807). All sites are close to the equator, at water depths ranging from 2,500 m to 3,900 m. Sites 803 and 807 penetrated into basement (26 m and 149 m, respectively). The K/T boundary was recovered at both of these sites. Neogene sedimentation rates decrease with depth, as expected, but this decrease is much greater than calculated from carbonate content, under the assumption that carbonate dissolution is the sole cause of the decrease. At any one site, sedimentation rates vary by a factor of more than two, with a striking maximum in the latest Miocene to early Pliocene, and strong minima in late early to early middle Miocene and in the Pleistocene. Many acoustic reflectors correlate between sites, within the limits of stratigraphic resolution. This suggests paleoceanographic events as a cause, generating changes in physical properties of sediments at the time of deposition. Many of the reflectors occur at carbonate reduction events (CRE's). Some apparently are the product of diagenetic enhancement of property changes, as, for example, within the ooze/chalk transition (which is diachronous). The interval corresponding to the Cretaceous/Tertiary (K/T) transition in the area is characterized by the presence of a deep CCD. The sequence at one site is calcareous; that at the other, is not. The fact that the two K/T sections recovered occur in sequences with major hiatuses suggests special conditions for preservation during the transition. We propose early cementation caused by high silicate concentrations in an ocean with greatly reduced productivity. The basalt cored at Sites 803 and 807 is predominantly aphyric to sparsely olivine or plagioclase phyric; the last flows are Albian to Aptian in age. At Site 807, pillow lavas buried sediments. One very thick flow (∼28 m) was penetrated here, possibly a flood basalt, indicative of massive outpourings on Ontong Java Plateau during the middle Cretaceous.