ALBERT

Beschreibung: The mineralogy of the lower Oligocene to Quaternary sediments of core CRP-2/2A drilled on the continental shelf of McMurdo Sound in Ross Sea, Antarctica, was examined by the X-ray diffraction method. Quartz, plagioclase feldspar and K-feldspar are the most important non-clay minerals. Pyroxene and amphibole occur in minor amounts throughout the core. The composition of the sediments points to an origin in the Transantarctic Mountains for the majority of the detrital components. There, the plutonic and metamorphic rocks of the basement, the sediments of the Beacon Supergroup and the volcanic rocks of the Ferrar Group could serve as possible source lithologies. The distribution of the detrital minerals reflects a long-term history of successive erosion and valley incision. During the deposition of the lower part of the core, the detrital minerals were probably mainly derived from the sediments of the Beacon Supergroup, as indicated by the high quartz but relatively low feldspar abundances. In the upper c. 350 m of the core, the influence of a source in the basement became stronger and results in lower quartz contents but increasing abundance of feldspar. Some diagenetic alteration of the sediments is indicated by the occurrence of zeolites below c. 320 mbsf and of opal-CT above c. 320 mbsf.

Beschreibung: Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct faunal assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some faunal exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively.

Beschreibung: The heavy mineral assemblages of the Lower Pliocene to Quaternary glacial sediments of the CIROS-2 drill site, situated near the mouth of Ferrar Glacier on the McMurdo Sound shelf, Antarctica, were analysed by optical means in order to reconstruct the source areas and dynamics of the late Cenozoic Antarctic ice masses. The assemblages are dominated by pyroxenes, amphiboles, altered minerals and opaque minerals. Within the pyroxene group, clinopyroxenes are most abundant; within the amphibole group, green and brown hornblendes are dominant. Other important heavy minerals present in minor amounts are zircon, titanite, epidote, garnet and apatite. The downcore distribution of the heavy minerals allows a subdivision of the sedimentary sequence into two major units, which can both be further subdivided into two subunits. The Pliocene interval between 166 and 110 mbsf is characterized by relatively high concentrations of apatite, zircon, titanite, garnet, epidote and green hornblende. This assemblage accounts for some 40–60% of the heavy minerals and points to a source to the west of the drill site, in the Transantarctic Mountains, where intrusive, metamorphic and sedimentary rocks cover large areas. The interval 166–137 mbsf (Lower Pliocene) contains additional brown hornblende and palagonite, indicative of a volcanic, probably hyaloclastitic source, which possibly has to be sought beneath the ice of the Ferrar Glacier. In contrast, the uppermost Pliocene and Quaternary interval between 110 mbsf and the top of the core is characterized by high concentrations of clinopyroxenes, altered minerals and opaque minerals. This record points to a main source area in the south or east, where large areas are occupied by basaltic rocks of the McMurdo Volcanic Group. A slight change in the composition of the pyroxene group occurs within this interval, at 48 mbsf. Thus, the heavy minerals in the sediments of core CIROS-2 document different source areas and therewith major changes in the ice dynamics. During the Pliocene the ice discharged through the Transantarctic Mountains into the McMurdo Sound. The source area shifted in the Quaternary to the south, to the region of the present-day Ross Ice Shelf.

Beschreibung: The organic and isotopic geochemical study of two sediment cores (KH-79-3, L-3, and KH-79-3, C-3) from the Oki Ridge in the Japan Sea has revealed that total organic carbon (TOC) mass accumulation rates are extremely high in the 12-11 ka (calendar age) interval and TOC in the sections in the 24-17 ka interval is depleted in 13C by 3.5 per mil relative to Holocene sediments. Alkenone sea surface temperature (SST) shows a decrease from 18° to 14°C from 17.5 to 11.6 ka and a sharp increase from 14° to 19°C from 11.6 to 11.1 ka. The SST changes are associated with the inflow of cold seawater with the vertical water mixing and the inflowof warm Tsushima Current into the Japan Sea. The d13C values for both 24-methylcholesta-5,22-dien-3?-ol (diatom marker) and dinosterol (dinoflagellate marker), are at their minimum from 24 to 17 ka, while those for long-chain alkenones are not. The theoretical considerations on d13C for biomarkers suggest low photosynthetic carbon demand of diatoms and dinoflagellates from 24 to 17 ka.

Beschreibung: A study of the C37 alkenone compositions in suspended particulate matter in the northwestern Mediterranean Sea has shown a correspondence between Uk'37 and sea surface temperature that significantly deviates from the general equation regularly observed in most marine world areas (Müller et al., 1998, doi:10.1016/S0016-7037(98)00097-0). However, the temperatures measured in the core top sediments using the general equation are in agreement with the annual average water column temperatures between 0-40 m depth. These discrepancies suggest that despite the rather constant correlation between UK'37 and seawater temperature throughout the world oceans, specific calibrations should be developed for each new area of application of the C37 alkenones for paleotemperature determination.

Beschreibung: New values for the astronomical parameters of the Earth's orbit and rotation (eccentricity, obliquity and precession) are proposed for paleoclimatic research related to the Late Miocene, the Pliocene and the Quaternary. They have been obtained from a numerical solution of the Lagrangian system of the planetary point masses and from an analytical solution of the Poisson equations of the Earth-Moon system. The analytical expansion developed in this paper allows the direct determination of the main frequencies with their phase and amplitude. Numerical and analytical comparisons with the former astronomical solution BER78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated. The corresponding insolation values have also been computed and compared to the former ones. This analysis leads to the conclusion that the new values are expected to be reliable over the last 5 Ma in the time domain and at least over the last 10 Ma in the frequency domain.

Beschreibung: The microstructures observed in the hydrogenetic ferromanganese crusts of neogene age sampled on the West African margin of the Central and Equatorial Atlantic are laminated. Three types of laminae were recognized. Several arguments, in particular TEM observations of ultra-thin sections, indicate that the laminae probably correspond to mineralized microbial films. The study of quaternary to recent ferromanganese coatings sampled in the Atlantic and in the Mediterranean Sea leads to the same conclusion. The mineralization of the biofilm is a step process. The sequestration of Fe and of variable amounts of Si preceeds the Mn scavenging. The type of lamina depends on the general hydrologic conditions of the bottom waters (currents activity, nutriments and Mn availability) but, also, on the microtopography of the sea water-lamina interface, probably because it introduces significant differences about Eh and Mn fluxes. Considering the low accretion rate of this type of deposit, it appears that the biofilm growth may be controled by a self-regulating process: the initial period of active production is followed by a long time interval of low production or of equilibrium between accumulation and removal of slime.

Beschreibung: The vertical distribution (0 to 100 m) and abundance of nanoflagellates were examined in the oligotrophic Aegean Sea (east Mediterranean) in early spring (south basin) and late summer (north and south basins) of 1997 in the framework of the MATER project (Mass Transfer and Ecosystem Response). Different trophic types of nanoflagellates (mixotrophic, heterotrophic, and phototrophic) were identified based on the possession of chloroplasts and the consumption of Fluorescently Labelled Minicells (FLM). Bacterial production (leucine method) was compared with bacterivory estimated from FLM consumption. We found that mixotrophic nanoflagellates played a small role as bacterivores relative to heterotrophic nanoflagellates and total bacterivory roughly balanced bacterial production. In early spring with cool (14.2°C) well-mixed water columns, flagellate concentrations were lowest, phototrophic flagellates were the dominant group and concentrations varied little with depth. Average concentrations of mixotrophs, heterotrophs and autotrophs were 0.07, 0.34, and 0.64 x 103 cells/ml, respectively. Bacterial production in the 0 to 100 m layer averaged about 0.74 µg C/l/d. Estimated nanoflagellate bacterivory from FLM ingestion accounted for 40% of bacterial production with mixotrophic nanoflagellates consuming 5% of bacterial production. In late summer, total nanoflagellate concentrations were higher. Average concentrations of mixotrophs, heterotrophs and autotrophs were 0.09, 1.14, and 0.66 x 103 cells/ml, respectively, in the southern basin and 0.09, 1.1, and 0.98 x 103 cells/ml, respectively, in the northern basin. In September, bacterial production for both basins roughly balanced estimated nanoflagellate consumption. Similar to the March estimates, mixotrophic nanoflagellates accounted for about 5% of nanoflagellate bacterivory. In a nutrient enrichment experiment in March, treatments including phosphorus resulted in increased bacterial production and reductions in identifiable mixotrophs.