Indian Ocean

Tropical Indian Ocean planktonic and benthic foraminifera have 13C/12C ratios which change abruptly within Magnetic Epoch 6 about 6.2 million years ago. All species analyzed in the Late Miocene section of DSDP Site 238 show a shift towards lighter values of delta13C by about 0.8?. The oxygen isotope signal indicates that the pre-shift period is climatically quiet while the post-shift period has strong fluctuations.

Two water samples and two sediment samples taken in 1965 by the R. V. "Meteor" in the area of the hot salt brine of the Atlantis II-Deep were chemically investigated, and in addition the sediment samples were subjected to X-ray and optical analysis. The investigation of the sulfur-isotope-ratios showed the same values for all water samples. This information combined with the Ca-sulfate solubility data leads us to conclude that, for the most part, the sulfate content of the salt brine resulted from mixing along the boundary with the normal seawater.

Sediments from a 3.40 m core out of the Persian Gulf were investigated for their content of straight chain paraffins and fatty acids. The samples range in age between 2000 and 9000 years (C-14-age of organic C). They contain 100-300 ppm of extractable fatcompounds and 20-70 ppm of hydrocarbons. There is no connection between the original distribution of the homologous series of n-fatty acids and n-paraffins. However, there is evidence that part of the n-fatty acids was reduced to n-paraffins, although the sediment itself does not look as if it were deposited under reducing conditions.

Bolboforma were recovered from all sites of Ocean Drilling Program (ODP) Leg 120 to the Central Kerguelen Plateau in the southern Indian Ocean. Eight Paleogene taxa, ranging from middle Eocene through early Oligocene, and nine Neogene taxa, ranging from late middle Miocene through earliest Pliocene, were recognized. A Bolboforma zonation recently proposed for the middle Paleogene of the Leg 114 sites from the southern Atlantic Ocean is applicable to the Leg 120 material from the southern Indian Ocean. The age of zonal boundaries is consistent within a resolution of +/- 1 m.y.

Changes in ancient oceanic current patterns have been strongly influenced by plate tectonics, particularly by the opening or closing of gateways between different oceans. Such modifications of oceanic circulation have important consequences on climate. We studied the Nd seawater isotopic composition of Indian and Pacific Ocean cores using Nd isotopes, which are good paleo-oceanographic tracers. We focused on the past 25 Ma which are marked by the closure of the Indonesian gateway as well as the Mediterranean connection.

An Oligocene-basal Miocene (Zones P19-P22/N4) oxygen and carbon isotope stratigraphy is presented based on mixed benthic foraminiferal faunas and different species of planktic foraminifers from Eastem Indian Ocean ODP Hole 758A. Lack of covariance in planktic and benthic delta18O ratios indicates that many Oligocene sea level fluctuations, including the major fall at 30 Ma, are not of glacio-eustatic origin. Delta18O values suggest that test morphology is a poor indicator of preferred depth habitat of Oligocene planktic foraminifers.

Stable and radiogenic isotopic and sedimentological data from sub-Antarctic deep sea sediment cores reveal a temporal link between changes in seawater 87Sr/86Sr ratios and major episodes of late Eocene-early Oligocene climate change. The 87Sr/86Sr records show two major inflections, one at 38-39 Ma near the middle/late Eocene boundary, followed by another at 33.4 Ma.

The scope of this research was to find out, how important is the presence of brackish water for the formation of the characteristical littoral subsoil fauna in the interstitial spaces of beaches. There is little precipitation in the Red Sea area and therefore little influence of freshwater on the beach. Moreover, the sandy beach of Sarso Island (Farasan Archipelago) is bordered landwards and underneath by solid limestone, preventing subsoil fresh water, if there is any, from penetrating into the beach region.

During Ocean Drilling Program Leg 120, an almost complete Paleogene sediment section on the Kerguelen Plateau in the southern Indian Ocean was recovered. The biostratigraphy of radiolarians from these sediments at Sites 748 and 749 is studied. A biostratigraphic framework established in low and middle latitudes is not applicable because of the absence of most zonal marker species. Biogenic opal is present only in middle Eocene to Oligocene sediments, and three new zones-Lychnocanoma conica, Axoprunum (?) irregularis, and Eucyrtidium spinosum zones-are proposed.

Layered Fe-Mn crusts from the off-axis region of the first segment of the Central Indian Ridge north of the Rodrigues Triple Junction were studied geochemically and mineralogically. Vernadite (delta-MnO2) is the main mineral oxide phase. 230Thxs and Co concentrations suggest high growth rates of up to 29 mm/Myr and a maximum age of the basal crust layer of 1 Ma. Whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation, Co, Pb, Ni and Ti concentrations are strikingly lower.