ALBERT

Beschreibung: General Subject of research: Detailed study of the shallow water hydrothermal system around Kolbeinsey and Grimsey islands

Beschreibung: Test specimens of methane hydrate were grown under static conditions by combining cold, pressurized CH4 gas with H2O ice grains, then warming the system to promote the reaction CH4 (g) + 6H2O (s???l) ??? CH4??6H2O. Hydrate formation evidently occurs at the nascent ice/liquid water interface, and complete reaction was achieved by warming the system above 271.5 K and up to 289 K, at 25-30 MPa, for approximately 8 hours. The resulting material is pure methane hydrate with controlled grain size and random texture. Fabrication conditions placed the H2O ice well above its melting temperature before reaction completed, yet samples and run records showed no evidence for bulk melting of the ice grains. Control experiments using Ne, a non-hydrate-forming gas, verified that under otherwise identical conditions, the pressure reduction and latent heat associated with ice melting is easily detectable in our fabrication apparatus. These results suggest that under hydrate-forming conditions, H2O ice can persist metastably at temperatures well above its melting point. Methane hydrate samples were then tested in constant-strain-rate deformation experiments at T= 140-200 K, Pc= 50-100 MPa, and ????= 10-4-10-6 s-1. Measurements in both the brittle and ductile fields showed that methane hydrate has measurably different strength than H2O ice, and work hardens to a higher degree compared to other ices as well as to most metals and ceramics at high homologous temperatures. This work hardening may be related to a changing stoichiometry under pressure during plastic deformation; x-ray analyses showed that methane hydrate undergoes a process of solid-state disproportionation or exsolution during deformation at conditions well within its conventional stability field.

Beschreibung: Grain‐size‐dependent flow mechanisms tend to be favored over dislocation creep at low differential stresses and can potentially influence the rheology of low‐stress, low‐strain rate environments such as those of planetary interiors. We experimentally investigated the effect of reduced grain size on the solid‐state flow of water ice I, a principal component of the asthenospheres of many icy moons of the outer solar system, using techniques new to studies of this deformation regime. We fabricated fully dense ice samples of approximate grain size 2±1 μm by transforming “standard” ice I samples of 250±50 μm grain size to the higher‐pressure phase ice II, deforming them in the ice II field, and then rapidly releasing the pressure deep into the ice I stability field. At T≤200 K, slow growth and rapid nucleation of ice I combine to produce a fine grain size. Constant‐strain rate deformation tests conducted on these samples show that deformation rates are less stress sensitive than for standard ice and that the fine‐grained material is markedly weaker than standard ice, particularly during the transient approach to steady state deformation. Scanning electron microscope examination of the deformed fine‐grained ice samples revealed an unusual microstructure dominated by platelike grains that grew normal to the compression direction, with c axes preferentially oriented parallel to compression. In samples tested at T≥220 K the elongation of the grains is so pronounced that the samples appear finely banded, with aspect ratios of grains approaching 50:1. The anisotropic growth of these crystallographically oriented neoblasts likely contributes to progressive work hardening observed during the transient stage of deformation. We have also documented remarkably similar microstructural development and weak mechanical behavior in fine‐grained ice samples partially transformed and deformed in the ice II field.

Beschreibung: In the nodule field of the Peru Basin, situated south of the zone of high bioproductivity, a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments. Maximum abundance (50 kg m−2) of diagenetic nodules is found near the calcite compensation depth (CCD), currently at 4250 m. There, the accretion rate of nodules is much higher (100 mm Ma−1) than on ridges (5 mm Ma−1). Highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary. There, distinct diagenetic growth conditions prevail and layers of dense laminated Mn oxide of very pure todorokite are formed. The layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments. The frequency of such movements is much higher than that of climatic changes. Two types of nodule burial occur in the Peru Basin. Large nodules are less easily moved by organisms and become buried. Consequently, buried nodules generally are larger than surface nodules. This type of burial predominates in basins. At ridges where smaller nodules prevail, burial is mainly controlled by statistical selection where some nodules are not moved up by organisms.

Beschreibung: Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ΣREEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ΣREE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.

Beschreibung: Many natural sands have a structure that is imparted to them during their geological life and that significantly modifies their pre-failure behaviour when compared with that of the reconstituted material. Unlike clays, for which emphosis has been given to both the bonding and fabric components of structure, for sands structure has generally been simply identified with bonding, whereas the effects of fabric have often been overlooked. An understanding of the way in which these components of structure influence the yielding and stiffness of these materials is required to formulate costitutive models that can adequately predict their response. The paper examines the pre-failure behaviour of two structured sands in triaxial compression performed over a wide range of pressures. Since yielding occurred at small strains, laboratoty techniques were developed to produce reliable and accurate determinations of stiffness ranging from 1 microstrain to failure. The influence of structure on the shear stiffness was investigated by comparing the behaviour of intact and reconstituted soils after accounting for differences in state. To explain how bond degradation developed, the study focused in particular on the shear behaviour between yielding and failure. The bond degradation resulted in a progressive transformation of the structured soil into a frictional material, giving rise to changes in the yield stress and shear stiffness that contrasted with the strain-hardening behaviour of the unbonded sands. As bonding degraded, the variation of the shear stiffness with state was seen to depend on which structural feature was predominant.

Beschreibung: A study of the echo peak amplitudes from known nodule areas is initiated to observe the acoustic response for varying nodule abundances and number densities. A statistical study of the peak amplitudes from different nodule areas confirms that the coefficient of variation is the highest for medium nodule abundance and number density. Echo fluctuation study based on the Rician probability density function (PDF) establishes that the non‐nodule sediment bottom contributes to less scattering, i.e., it is a microtopographic type, whereas scattering is dominant in the nodule‐bearing areas. The spectral studies are conducted on depth data of different areas. This study ensures that the signal scattering in the nodule bottom area is due to the nodules lying on the seabed rather than the large / small‐scale topographic variations. The study based on Poisson PDF for nodule area confirms this fact again. Agreement between the nodule distribution and the Poisson distribution parameter is clearly seen. Such a relation is not observed in the case of Rician density functions.

Beschreibung: Coelacanths Latimeria chalumnae are the only living representatives of crossopterygian fish close to the roots of our own vertebrate history and therefore occupy a unique position among living fossils. L. chalumnae has become a synonym for long evolutionary age, timeless existence, tenacity, immortality and links to old roots, appearing in language, poetry, fiction and many art forms. It is a symbol of a new national identity in the Comoro Archipelago, Western Indian Ocean. I consider here the intrinsic and extrinsic value of coelacanths and the role of these fish in biodiversity conservation. The fate of coelacanths lies in our hands. It will be a measure of the success or failure of eco-ethics in ecology.

Beschreibung: A method for attaching acoustic transmitters externally to deep-water fishes in situ is described. Tags, each comprising a transmitter connected to a dart, were fired at fish from a pneumatic gun held by the manipulator arm of a submersible. The method was applied successfully for tagging coelacanths and may have application for use with other species of fishes living at depths to about 1000 m. The usefulness of direct observation for monitoring the effects of tags on fish is evaluated in relation to the effects of the tagging method on coelacanths.

Beschreibung: Plastic debris accumulates in the marine environment following its use in agricultural, industrial and social activities. Its ultimate fate is accomodation in sediments where it may persist for times up to centuries or longer. There appears to be an increasing flux of materials with time and an increased areal coverage of the benthos. Impacts upon bottom organisms can take many forms. Systematic monitoring tactics for the extent of seafloor coverage by plastics are yet to be incorporated into national programs.

Beschreibung: Benthic foraminifera and surface sediments were analyzed from 23 box-core and core-top samples from 250 to 3600 m depth at the southern Portuguese continental margin between 37 and 38 °N. This area is affected by the MOW which flows northwards along the slope between 600 and 1500 m waterdepth. Sediment structures, grain-size distribution and clay mineral assemblages of surface sediments indicate active winnowing in the upper part of the MOW, and deposition of the fine fraction near its lower boundary. R-mode cluster analyses of foraminiferal census data from the 〉 250 μm fraction revealed four associations. The ‘Shelf Edge Association’ occurs on glauconitic shelf and upper slope sands down to 268 m. The ‘Upper Slope Association’ is recognized between 498 and 1300 m where sand-silt-clays to clayey silts are encountered. The ‘Lower Slope Association’ is found between 1405 and 2985 m and differs markedly from assemblages below 3000 m (‘Deep Water Association’) where the near-surface sediments are soft hemipelagic clays. The ‘Boundary Layer Association’ shows no significant depth limits but abundance maxima both in the density interface above the MOW and in the interval of decreasing turbulence below it. The boundaries of the ‘Shelf Edge’ and ‘Upper Slope Association’ correspond to these hydrographic boundary layers whereas the boundary between ‘Lower Slope’ and ‘Deep Water Assemblage’ is related to threshold values of nutrient flux to the benthic community. Examination of hard-substrates reveals 27 different species of epibenthic foraminifera. Six of these, the ‘Epibenthos Group’, were found attached to elevated substrates only within the MOW. Above the MOW, elevated substrates were inhabited by different species, whilst below the MOW they were not used by any epibenthic foraminifers. Evidently, the hydrodynamic environment of the MOW current provides an ecological niche which is efficiently used by opportunistic suspension feeders. The ‘Epibenthos Group’ is more abundant in the middle part of the study area between 37 °20′ and 37 °40′N where the sand content of surface sediments is also higher. Both indicate an enhanced sediment-water interaction in this area which results from an obstruction of the MOW flow by the ‘Principes d'Avis’ basement spur.

Beschreibung: Derivation and application to Central Alps of 3-D seismic crustal structure modeling by use of a large number of criss-crossing controlled-source seismology profiles.

Beschreibung: During the ARCTIC '91 expedition aboard RV Polarstern (ARK VIII/3) to the Central Arctic Ocean, a box corer sample on the Gakkel Ridge at 87 degrees N and 60 degrees E yielded a layer of sand-sized, dark brown volcanic glass shards at the surface of the sediment core. These shards have been investigated by petrographic, mineralogical, geochemical and radiogenic isotope methods. The nearly vesicle-free and aphyric glass shards bear only minute microphenocrysts of magnesiochromite and olivine (Fo(88-89)). Most glasses are fresh, although some show signs of incipient low-temperature alteration. From their shapes and sizes, the glass shards most likely formed by spalling of glassy rinds of a nearby volcanic outcrop. Geochemically, the glasses are relatively unfractionated tholeiites with E-MORB trace element compositions. Thus, they are quite similar to the previously investigated ARK IV/3-11-370-5 basalts from 86 degrees N. The Nd and Sr isotopic ratios of PS 2167-2 glasses are significantly lower than for ARK IV/3-11-370-5 basalts and suggest an isotopically heterogeneous mantle source of Gakkel Ridge MORE between 86 degrees and 87 degrees N. The positive Delta-8/4 Pb value (similar to 16) and high Sr-87/Sr-86 ratio (0.70270), found for PS 2167-2 glasses are similar to that of ARK IV/3-11-370-5 basalts and show the influence of the DUPAL isotopic anomaly in the high Arctic mantle. These results argue against the presence of an 'anti-DUPAL anomaly' in the mantle below the North Pole region and simple models of whole-mantle convection.

Beschreibung: A theoretical model of CO2aq-dependent phytoplankton carbon isotope fractionation (єp) and abundance (δ13Corg) is compared to observed isotopic trends with temperature and [CO2aq] in the ocean. It is shown that the model's δ13Corg response to surface ocean temperature and to [CO2aq] can simulate observed trends when the other independent model variables (phytoplankton cell growth rate, cell size, cell membrane CO2 permeability, and enzymatic isotope fractionation) are held at realistic, constant values. The possible contribution made by each of these variables to the residual scatter in δ13Corg about its trends with temperature and [CO2aq] is quantified, thus estimating a maximum isotopic sensitivity to changes in each of these variables. The model response to growth rate and especially cell size, however, appears to be unrealistically high. This may occur because the net isotopic effects of such factors may be attenuated through dependent and isotopically offsetting variations among variables. The model's indicated sensitivity to such factors as CO2 permeability, enzymatic fractionation, cell size, and cell surface area/volume provides mechanisms whereby changes in species composition can play a significant role in affecting observed variations in oceanic δ13Corg. Overall, the model is consistent with earlier suggestions that marine δ13Corg and єp variability can be explained by carbon isotope fractionation evoked by CO2aq-dependent phytoplankton. This has important implications for interpreting carbon isotopic variability encountered in plankton and their organic constituents in the present-day ocean and in the marine sedimentary record.

Beschreibung: The partial pressure of CO2 (pCO2) was measured during the 1995 South-West Monsoon in the Arabian Sea. The Arabian Sea was characterized throughout by a moderate supersaturation of 12–30 µatm. The stable atmospheric pCO2 level was around 345 µatm. An extreme supersaturation was found in areas of coastal upwelling off the Omani coast with pCO2 peak values in surface waters of 750 µatm. Such two-fold saturation (218%) is rarely found elsewhere in open ocean environments. We also encountered cold upwelled water 300 nm off the Omani coast in the region of Ekman pumping, which was also characterized by a strongly elevated seawater pCO2 of up to 525 µatm. Due to the strong monsoonal wind forcing the Arabian Sea as a whole and the areas of upwelling in particular represent a significant source of atmospheric CO2 with flux densities from around 2 mmol m−2 d−1 in the open ocean to 119 mmol m−2 d−1 in coastal upwelling. Local air masses passing the area of coastal upwelling showed increasing CO2 concentrations, which are consistent with such strong emissions.

Beschreibung: The ability to monitor the heat content of oceans over long distances is becoming increasingly important for understanding the role of oceans in climate change, for determining the variability of the state of the oceans, for operational ocean observing systems, and for studying large-scale ocean processes such as water-mass formation. Although the properties of the upper layers of the ocean can be routinely measured on large scales by satellite remote sensing (providing altimetric and infrared data) and with expendable probes dropped from commercial vessels, the deep interior of the ocean is more difficult to monitor. Ocean acoustic tomography1 is a promising technique for such applications, as it has the potential to provide systematic, instantaneous and repeated measurements of the ocean interior over large parts of an ocean basin. Here we demonstrate the capability of this technique for measuring the heat content across an entire (albeit small) ocean basin—the western Mediterranean Sea.

Beschreibung: Water samples from surface and bottom waters of two bights of the Baltic Sea were analysed for dissolved and/or particulate concentrations of Al, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb and Zn, in addition to the main oceanographic variables, at 27 stations during six cruises between February 1990 and July 1992. The metal values show distinct regional differences, with maximum concentrations at the near-shore stations, The levels of total Hg exhibit a significant negative relationship with salinity. In surface layers, seasonal differences due to biogenic uptake of elements could not be detected for any of the dissolved metals. In bottom waters, however, summer-time concentrations of a number of metals are in clear excess of winter levels either due to diffusion of metals (Go, Fe, Mn) from the sediments under low-oxygen or anaerobic conditions, or due to mineralization processes (Cd, Zn) of recently sedimented biogenic particulates. With the exception of Fe and Pb, the particulate fractions are of minor importance, with slight variabilities between the seasons only. The K-D values (ratio between metal concentrations in the particulate and dissolved fractions) decrease by more than two orders of magnitude in the order Fe-Pb-Mn-Co-Zn-Cd-Cu-Ni. Finally, the results are discussed with regard to a trace metal monitoring programme in the area.

Beschreibung: The output of the global eddy‐resolving ¼° ocean model of Semtner/Chervin (run by the Naval Postgraduate School, Monterey, California) has been used to study the oceanic temperature and heat flux in the Indian Ocean. The meridional heat flux in the northern Indian Ocean is at the low end of the observed values. A vertical overturning cell in the upper 500 m is the main contributor to the annual mean meridional heat flux across 5°S, whereas the horizontal gyre circulation, confined to the upper 500 m, dominates north of the equator. The change of monsoon winds is manifested in a reversal of the meridional circulation throughout the whole water column. The most notable result is a strong linear relationship of the meridional temperature flux and the zonal wind stress component north of 20°S. The model's Pacific‐Indian Ocean throughflow across the section at 120°E accounts for −8.8±5.1 Sv (1 Sv≡106 m3 s−1). A strong interannual variability during the model run of 3 years shows a maximum range of 12 Sv in January/February and a minimum during March through June. The inflow from the Pacific into the Indian Ocean results in a total annual mean temperature flux of −0.9 PW (1 PW≡1015 W). In the model the temperature flux from the Pacific through the Indian Ocean to the south dominates in comparison with the input of solar heat from the northern Indian Ocean.

Beschreibung: Plate collision cuases expulsion of fluids and gases and material turnover in the deep ocean along the global subduction zones. Such cold vents are characterized by mineral precipitates and characteristic assemblages of macro organisms. The latter harbor symbiotic bacteria which utilize the chemically-reduced constituents (CH4 and H2S) of the expelled fluids as their energy and supply their host with food. The interaction between tectonically-induced fluid flow and pumping activity of the vent fauna sets up a shallow recirculation system whose magnitude can be estimated from direct measurements by an in situ vent sampling device (VESP) in connection with tracer studies. The dewatering rates based on the biogeochemical estimates agree surprisingly well with those derived from geophysical estimates.

Beschreibung: From geostrophic calculations the exchange of deep water from the Somali into the Arabian Basin through the Owen Fracture Zone has been estimated to be about 2 Sv, with a seasonal modulation of the same magnitude. After leaving the Fracture Zone, the flow bifurcates into a northern and a southern branch, each closely following the slope of the Carlsberg Ridge. The weaker vertical gradients of the hydrographic properties in the deep Arabian Basin are consistent with enhanced vertical mixing at the rugged topography over the Carlsberg Ridge.

Beschreibung: The gene coding for the anion-specific porin of the halophilic eubacterium Ectothiorhodospira (Ect.) vacuolata was cloned and sequenced, the first such gene so analyzed from a purple sulfur bacterium. It encodes a precursor protein consisting of 374 amino acid (aa)-residues including a signal peptide of 22-aa residues. Comparison with aa sequences of porins from several other members of the Proteobacteria revealed little homology. Only two regions showed local homology with the previously sequenced porins of Neisseria species, Comamonas acidovorans, Bordetella pertussis, Alcaligenes eutrophus, and Burkholderia cepacia. Genomic Southern blot hybridization studies were carried out with a probe derived from the 5′ end of the gene coding for the porin of Ect. vacuolata. Two related species, Ect. haloalkaliphila and Ect. shaposhnikovii, exhibited a clear signal, while the extremely halophilic bacterium Halorhodospira (Hlr.) halophila (formerly Ect. halophila) did not show any cross-hybridization even at low stringency. This result is in good accordance with a recently proposed reassignment within the family Ectothiorhodospiraceae, which included the separation of the extremely halophilic species into the new genus Halorhodospira.

Beschreibung: Rubrik "Neues aus dem Geologenarchiv (1997)"

Beschreibung: (collected results from the GEOMAR Bungalow Working Group)

Beschreibung: Stable carbon and oxygen isotopes of the polar planktic foraminifera Neogloboquadrina pachyderma sinistral from sediment cores of the Norwegian Sea reveal several anomalous 13C and δ18O depletions in the surface water during the last glacial to interglacial transition and during the later Holocene. The depletions that are observed between the Last Glacial Maximum (LGM) and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs, which consequently resulted in a stratification of the uppermost surface water layer and a non-equilibrium between the water below and the atmosphere. At ~8.5 ka (14C BP) this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice-rafted detritus. After this time, the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers. However, this post-deglacial evolution towards a modern-type oceanographic environment was interupted by a hitherto undescribed isotopic event (~7–8 ka) which, on a regional scale, is only identified in eastern Norwegian Sea surface water. This event may be associated with the final pulse of glacier meltwater release from Fennoscandia, which affected the onset of intensified coastal surface water circulation off Norway during a time of regional sea-level rise. All these data indicate that surface water changes are an integral part of deglacial processes in general. Yet, the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later Holocene when from a climatic point of view relativelystable conditions prevailed.

Beschreibung: The Russian icebreaker KAPITAN DRANITSYN carried out the TRANSDRIFT III expedition to the Laptev Sea (October 1 to 30., 1995), the largest ice factory in the Arctic Ocean and source region of the Transpolar Drift. In this shelf region, ice free for only three months a year, a comprehensive interdisciplinary working program concerning the causes and effects of annual freeze-up was performed. Unlike our previous expeditions to the Laptev Sea, which focused On oceanographical, hydrochemical, ecological, and sedimentological processes during the brief ice-free period in summer, this expedition studied these processes during the extreme physical change through the onset of ice formation in autumn. This is the first study of its kind under these conditions, and gave important clues to the rapid (14 to 40 days) freeze-up, which has significant year-round effects for the Laptev Sea and global environment. Freeze-up began one month later than usual (a 40 year record) close to the Novosibirskie Islands in low salinity surface waters due to heat stored in an intermediate water layer between 10 and 25 m water depth. Later, huge tracts of turbid, dirty ice were found off the Lena Delta where an unusually high phytoplankton concentration for this time of year occurred. The origin of these anomalies, and whether they are anomalies at all, and their relationship to global environment in real time are the focus of continuing research.

Beschreibung: Large oceanic changes occurred during the last transition from glacial to interglacial conditions (Termination I), which significantly affected pelagic and benthic environments. This study presents results of a quantitative investigation of benthic foraminifera at four sites distributed along a north-south transect across the northern North Atlantic with a high temporal resolution (k 200 years). Benthic foraminifera are examined in samples (1-2 cm sampling intervals) from four long sediment cores located in the southern Fram Strait, the Greenland-Iceland-Norwegian Sea (GIN Sea), and the Rockall Plateau. The most prominent species of benthic foraminifera include Oridorsalis nnlbolzatlls, Cibicidoides wl~ellerstoufi,C assidulina spp. group, P!jrgo rotalaria, Globocassidrrliiza sllbg-lobosa and tubes of agglutinated taxa. In each core, the climatic amelioration at Termination I is recorded to have occurred in two steps. A first INDAR maximum (INDividuals Accumulation Rate = ind/cm2 ky; GIN Sea: average 3,000-6,000 ind/cm2 ky, Rockall Plateau: average 150 ind/cm2 ky) is followed by a period of lower values. A second maximum reveals slightly lower values than the older maximum. Interglacial INDAR values average 700 ind/cm2 ky for the GIN Sea and 200 ind/cm2 ky on the Rockall Plateau. This is roughly twice that of typical glacial values. Meltwater events, identified by stable isotope data and sea-surface temperature reconstructions based on planktic foraminiferal transfer functions, are marked by an increase in endobenthic and opportunistic species. A decrease of reconstructed sea-surface temperatures appears synchronous with the relative INDAR minimum that occurs between the two INDAR maxima. The results indicate a close coupling of sea-surface processes to the benthic realm ("pelagic-benthic coupling") with a longitudinally variable strength. The climate signal at the Rockall Plateau revealed by the fossil benthic foraminifera shows a lower amplitude than that of the GIN Sea. The second, younger INDAR maximum is characterized by an increased abundance of epibenthic species at all core locations, suggesting extended lateral bottom currents. In comparison with various palaeo-climatological data sets, the variability of fossil benthic foraminiferal abundances in the GIN Sea show a distinct coherence with changes of atmospheric temperatures, sea-surface temperatures and the postglacial sea level rise. The variability of the benthic foraminiferal fauna is principally in phase with climate change events.

Beschreibung: From two cores of the central Arctic Ocean and the Southern Ocean (Weddell Sea) a new morphotype of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) (Ehrenberg) with "sausage" shaped final chambers (i.e. "Wurstkammer") is described. A comparison of these morphotypes in the two polar regions shows significant differences in shape and frequency during the last 70,000 years in the central Arctic Ocean and during the last 140,000 years in the Weddell Sea. In the central Arctic Ocean the frequency of wurstkammer specinlens call be correlated to that of the so-called kummerform specimens during the last 70,000 years; this correlation cannot be seen in a core from the Weddell Sea. The wurstkammer and kummerform specimens are interpreted as being end-members of a morphological progressional line. The abnormal chamber growth is probably an adaption to various environmental stress conditions found in the two polar regions during the last 70,000 in the Arctic and 140,000 years in the Antarctic, but the reasons for this abnormality are not yet fully understood.

Beschreibung: The Russian icebreaker KAPITAN DRANITSYN carried out the TRANSDRIFT III expedition to the Laptev Sea (October 1 to 30., 1995), the largest ice factory in the Arctic Ocean and source region of the Transpolar Drift. In this shelf region, ice free for only three months a year, a comprehensive interdisciplinary working program concerning the causes and effects of annual freeze-up was performed. Unlike our previous expeditions to the Laptev Sea, which focused On oceanographical, hydrochemical, ecological, and sedimentological processes during the brief ice-free period in summer, this expedition studied these processes during the extreme physical change through the onset of ice formation in autumn. This is the first study of its kind under these conditions, and gave important clues to the rapid (14 to 40 days) freeze-up, which has significant year-round effects for the Laptev Sea and global environment. Freeze-up began one month later than usual (a 40 year record) close to the Novosibirskie Islands in low salinity surface waters due to heat stored in an intermediate water layer between 10 and 25 m water depth. Later, huge tracts of turbid, dirty ice were found off the Lena Delta where an unusually high phytoplankton concentration for this time of year occurred. The origin of these anomalies, and whether they are anomalies at all, and their relationship to global environment in real time are the focus of continuing research.

Beschreibung: In vivo expression technology (IVET) has been used to identify 〉100 Salmonella typhimurium genes that are specifically expressed during infection of BALB/c mice and/or murine cultured macrophages. Induction of these genes is shown to be required for survival in the animal under conditions of the IVET selection. One class of in vivo induced (ivi) genes, iviVI-A and iviVI-B, constitute an operon that resides in a region of the Salmonella genome with low G+C content and presumably has been acquired by horizontal transfer, These ipi genes encode predicted proteins that are similar to adhesins and invasins from prokaryotic and eukaryotic pathogens (Escherichia coli [tia], Plasmodium falciparum [PfEMP1]) and have coopted the PhoPQ regulatory circuitry of Salmonella virulence genes. Examination of the in vivo induction profile indicates (i) many ivi genes encode regulatory functions (e.g., phoPQ and pmrAB) that serve to enhance the sensitivity and amplitude of virulence gene expression (e.g., spvB); (ii) the biochemical function of many metabolic genes may not represent their sole contribution to virulence; (iii) the host ecology can be inferred from the biochemical functions of ipi genes; and (iv) nutrient limitation plays a dual signaling role in pathogenesis: to induce metabolic functions that complement host nutritional deficiencies and to induce virulence functions required for immediate survival and spread to subsequent host sites

Beschreibung: THE celebrated French sense of smell, nurtured down the centuries on the fruity bouquets of fine wines, is now being applied to a less palatable subject: air pollution. Scientists are training volunteers in Grand Couronne, a village outside Rouen in northern France, to recognise the different smells given off by a local rapeseed oil factory that is accused of fouling the village’s air. They hope the results will help the factory to eliminate the offending chemicals from its emissions. Residents of Grand Couronne have been complaining of a sulphurous stench ever since the Saipol factory was built in 1993. But their objections were too subjective and unquantifiable for the factory to know what action to take. The new technique is designed to identify precisely those molecules responsible for the smell. The 17 volunteers are being trained over four months to distinguish the smells of 45 different molecules. They ...

Beschreibung: Abundance, biofacies and ATP content of benthic foraminifera (〉63 μm) were studied in the Northeast Water (NEW) Polynya (77–81°N, 5–17°W) over the ice-free summer, 1993, to investigate how a polynya system might influence the underlying benthic community. In the living assemblage, distinguished by Rose Bengal staining, over 60 taxa could be identified. The biofacies identified was similar to that of other Arctic shelf habitats. Foraminifera were counted in 3 size fractions (63–125 μm, 125–250 μm and 〉250 μm), with 65% of the foraminifera occurring in the smallest size fraction (63–125 μm). Total abundances (〉63 μm) in the uppermost 1 cm averaged approximately 200 ind/10 cm3 and declined down-core, as did the number of species. Abundances and species composition correlated positively with sediment chlorophyll and ATP content, with maxima occurring in the shallower northern regions of the polynya, suggesting a general dependence on food. Foraminera biomass was estimated to be 0.1-0.3 g Corg/m2. Abundances, biomass and ATP content were comparable to ice-free, deep-sea regions in the Norwegian Sea. Temporal changes observed over a 2 month period at one location were difficult to distinguish from spatial and analytical variability. Contrary to expectations, growth was unpronounced at the community and at a species level, implying either a delayed response of the benthic foraminiferal community to food inputs from the overlying water column or the presence of biological limitations other than food, such as predation.

Beschreibung: Calcareous benthic foraminifera from four cores from the southern flank of the Skagerrak (NE North Sea) were investigated in order to estimate the response of this fossil group to climate fluctuations during the upper part of the Holocene. Q-mode factor analyses were carried out for the most abundant taxa. The results reveal C. laeuigata, H. baltllica, M. barleeanus, G. turgida, B. mal;yirintn, and U. yeregrirtn as most conm~on/importantta xa. In the upper part of all cores B. skagerrakensis shows a significant increase and dominates the foraminifer fauna in cores from greater water depth. The data suggest no direct relation between the fluctuations of foraminifer assemblages and climate change. However, climate forced fluctuations in the strength of the water-circulation caused considerable changes in the foraminifer assemblages. Three major assemblages were used for environmental analysis: H. baltlticn dominated assemblages were identified as indicators for stagnant conditions. They characterize the oldest core sections, most probably the Holocene climate optimum. Cassidl~linala euigata assemblages seem to indicate increasing current strength, a process that is often associated with deteriorating climatic conditions. Briznlirtn skaCqcrrnkensis appears to have a certain relation to unstable water masses, and probably a tolerance for increasing polution of the North Sea since the advent of modern industrialization.

Beschreibung: The present investigation was initiated to report on species compositions and dynamics in the Norwegian-Greenland Sea during low production phases in spring and early summer. Thus, the distribution patterns of living coccolithophores during June to July, 1990, February and May, 1991, and March to April, 1995 were investigated. In general, the seasonal development of the phytoplankton started after the yearly dark period and coccolithophores increased in abundance when the water column was more stratified and both temperatures and insolation increased. Cell densities reached a maximum of 207x10~c occospheres/l in the southeastern part of the studied area. However, these high cell densities probably resulted from ,,old" populations, drifted to the Norwegian-Greenland Sea from the North Atlantic. Some of the collected samples did not contain any coccolithophores. In total, 15 coccolithophore species were identified. The diversity was generally higher in the eastern part of the Norwegian-Greenland Sea and to the west the coccolithophore communities often were monospecific. Emiliania huxleyi is the dominant species, but Calciopappus caudatus and Algirosphaera robusta also considerably contribute to the communities. High cell densities of C. caudatus were interpreted as the result of a bloom or more probably close to bloom conditions during the general low productive period. In addition, many of the E. huxleyi coccolith from the surface waters of the southeastern Norwegian-Greenland Sea were heavily corroded. These specimens may have drifted within the Atlantic water for a longer time.

Beschreibung: At a subtidal, soft-bottom site in the western Baltic Sea, mussel (Mytilus edulis) patches co-occur with high predator abundances. Sea star (Asterias rubens) biomasses, in particular, exceed reported values considered sufficient for restricting mussels to the intertidal zone. To determine how mussels can persist in the face of intense predation, we decomposed patch space occupancy into the relative contributions of newly arriving individuals (recruitment) and of increases in body size of the individuals already present in the patch over 13 mo. Sea stars, as major predators, were only able to control 77% of the potential per capita recruitment rate of 91 individuals/yr in 2 m depth. The remaining recruitment rate of 21 individuals/yr was sufficient to allow patches to occupy 1.6 times more space per year. Transplantation of patches to 6 m depth, where recruitment is negligible, revealed that sea stars were also ineffective in controlling mussel coverage through consumption of larger mussels (〉1 yr, 〉30 mm shell length). In deeper water, space occupancy of patches through increases in mussel body size was able to balance predation mortality, demonstrating that mussels attained a relative refuge in size at only 33 mm shell length. Based on the measured shell growth rates, mussels attain this size after ≈15 mo. In situ observations of Asterias feeding activity, the ratios between necessary predator sizes to attack prey of a given size, and predator size distributions suggest that sea stars were on average too small to feed effectively on adult (〉1 yr) mussels. Probably, Asterias cannot respond to abundant prey and increase its maximal body size at the site because salinities are at its lower tolerable limit (12–18 g/kg). Thus, bottom-up factors such as high prey productivity in concert with subtle size-based ineffectiveness of the predator population allow otherwise unstable predator–prey populations of a generalist predator and its preferred prey to coexist. Although mussel predators were unable to decimate mussels to local extinction, a release of experimental mussel patches from predation with strong recruitment (2 m depth) resulted in an approximately sevenfold yearly areal increase in shallow treatments, which would lead to a 100% mussel cover at the site within 1 yr. Given that mussels can dominate both rocky substratum and soft sediment, we also studied the effect of substratum quality in factorial combination with presence/absence of predation and water depth on mussel abundance. Attachment to stable substratum did not affect recruitment to the patches or patch space occupancy, but it completely prevented patch dislodgment and subsequent drift. In contrast to rocky shores, mussel patch dislodgment may represent the major mode of patch dispersal and new patch formation in soft-bottom environments as demonstrated by a drift collector fence.

Beschreibung: The present literature on biologically mediated fluxes from the benthic nepheloid layer (BNL) across the sediment-water interface into the sediment and vice versa is reviewed. The processes involved are categorised according to direct bioresuspension and biodeposition, i.e. direct interception of the animal with particles, and those effects, which are indirectly created by benthic organisms, e.g., changes of physical properties in the sediments, constructions like tubes and pits and the corresponding changes in hydrodynamic conditions. It is concluded that benthic organisms significantly increase the flux of particles across the interface and that the physically created fluxes are easily modified by a factor of 2 and more.

Beschreibung: The sedimentary system involves processes that weather rocks and reduce them to soluble and fine-grained particulate components that can be transported. deposited, and transformed back into rock. !Jost of the processes can be observed today, but the present is an unusual episode in our planet's history. We live in a brief warm interglacial epi sode in an interval usually characterized by large mid-and high-latitude icc sheets and a much lower sea level. To complicate matters further, few measurements of process rates were made before the significant impacts of agriculture and the industrial revolution altered them. Consequently, the rates at which different processes operate over most of geologic time arc not well known. The objective of modeling sedimentary systems is to simplify these processes so that they can be described in mathematical terms. Successful models predict the results of weathering. erosion, transport, depositional and diagenetic processes and allow us to determine process rates from ancient deposits. Modeling can also suggest the kinds of geologic information that can be used for its validation.

Beschreibung: The Japan Deep Sea Impact Experiment (JET) created a near Seafloor sediment plume in an attempt to reproduce conditions during manganese nodule mining in the Clarion-Clipperton zones in 1994. An image analysis technique of seafloor photos is developed for quantification of resedimentation of the plume. Colour differences between the nodules, black, and the sediments, light ocher, are used in the technique. A laboratory water tank test for calibration of the resedimentation is introduced. The colour changes, from black to light ocher of the nodules, in deep-sea photos observed after the resedimentation are analyzed by the technique. An example contour map of thickness of the resedimentation is presented.

Beschreibung: Two living forms of Globigerinella siphonifera (d'Orbigny), presently identified as Type I and Type II, can easily be distinguished and collected by SCUBA divers because of differences in appearance, arrangement of the rhizopodial network, and the presence or absence of commensals. Additional biological differences are apparent from laboratory culture experiments; Type I individuals survive significantly longer than Type II under conditions of darkness and starvation and have significantly slower chamber formation rates. Stable isotopic analyses of Types I and II also reveal notable differences, with Type I consistently yielding more negative S'^O and 8"C values. Results of Mg/ Ca ratio analyses indicate that Type II specimens precipitated their shells in slightly cooler (deeper) surface waters than Type I specimens. These observations and results from DNA sequencing unequivocally demonstrate that G. siphonifera Types I and II should be regarded as biological sister species. Contrarily, biometric analysis of the empty shells reveals few significant differences between G. siphonifera Types I and II. Of all the features measured from X-ray and SEM images of serially dissected specimens, only shell porosity yields readily discernible differences, with Type I adult chambers averaging 10-20% porosity and Type II adult chambers averaging 4-7% porosity. Statistically significant differences between Type I and II populations are revealed in maximum test diameter (Type I is typically larger) and coiling (Type I is typically more evolute), but these differences do not justify species level distinction of Types I and II using traditional paleontological species concepts. On the basis of the above evidence, and since all specimens were collected at the same location at ~ 3-8 m water depth, we conclude that G. siphonifera Types I and II are living examples of cryptic speciation, whereby biological speciation has occurred in the absence of discernable change in shell morphology. However, it is not clear when or where this speciation took place. Preliminary study of deep-sea cores from the Caribbean and Pacific sides of the Isthmus of Panama reveals a predominance of specimens with Type II porosity values, with rare occurrence of specimens yielding Type I porosity values. Systematic downcore measurement of shell porosity and tightness of coiling needs to be extended back to the middle Miocene, when G. siphonifera first appeared, to determine the timing of the Type I and II morphological divergence. Postulated mechanisms for reproductive isolation and speciation of Types I and II include alloparapatric, depth parapatric, and sympatric speciation. These models could be tested if further analysis of fossil G. siphonifera shells allows determination of the timing of speciation, the preferred depth distribution, and the history of geographic distribution of Types I and II.

Beschreibung: Troll Field represents the largest petroleum discovery within the entire North Sea area in oil equivalents, with 74% of the accumulated petroleum present as dry gas and 26% as a heavy biodegraded oil leg. The field is divided into several provinces based on the distribution of gas and oil, and the gas and oil have been suggested to be cogenetic. The migration and filling model presented in this paper suggests that the oil and gas represent two different migration phases and that gas migration and filling predate oil emplacement. Two different oil populations have been characterized and mapped in Troll field applying conventional geochemical techniques. We suggest that the two oil populations migrated into the structure through two different migration systems. Oil and gas were subsequently biodegraded within the reservoir. The two oil populations have been found in neighboring oil and gas discoveries, and an oil-oil correlation with these discoveries has been used to determine the location of field filling points and regional migration routes. When oil biodegradation terminated, fresh oil continued to migrate into the reservoir and mixed with the residue of the biodegraded oil. The field was tilted downward to the west in the Neogene, and oil and gas remigrated within the field with a possible spillage of gas. Tilting resulted in a dominantly upward movement of the oil phase whereas gas migrated laterally. Residual oils in the water zone have been used to reconstruct the paleoconfiguration of the field that controlled the current distribution of oil populations within Troll Field.

Beschreibung: The late Quaternary sedimentary history of the continental margin off Portugal was reconstructed from sediment gravity cores. Hemipelagic sedimentation (lithofacies A) was dominant during glacial times. It was interrupted periodically by deposition of shelf- and upper-slope-derived silty and sandy terrigenous material by dilute turbidity currents (lithofacies B and C), ice-rafted debris during distinct periods of breakdown of North Atlantic ice sheets (Heinrich events, lithofacies D) and large amounts of pteropods (lithofacies F). Settling of biogenic particulate material (lithofacies E) prevailed during the Holocene, when sea level and sea surface temperatures were high and terrigenous shelf-input was low. Downslope transport was dominant on the northern part of the Portuguese margin, culminating in frequent turbidity current transport between 35 and 70 ka. This may be due to a humid climate and a high fluvial input. Pteropod muds are confined to cores south of 41°N. Prominent peaks in pteropod concentration were radiocarbon dated at 17.8 and 24.6 ka. Layers rich in ice-rafted debris (IRD) were found along the entire margin. The base of these layers have been dated at 13.6–15.9 14C ka, 21.0–22.0 14C ka, 33.8 14C ka and ±64.5 ka, which correspond well with the ages of Heinrich events 1, 2, 4 and 6 in the central North Atlantic. Heinrich events 0 (10.5 ka), 3 (27 ka) and 5 (50 ka) rarely influenced sedimentation on the Portuguese slope. A mineralogical study of the IRD within Heinrich layers suggests that most icebergs were derived from the Laurentide Ice Sheet in the Hudson Strait and Hudson Bay area through the Labrador Current and the Canary Current and flowed in a southward direction along the margin. IRD from European ice sheets may have been mixed in during Heinrich event 6. On their way along the margin the icebergs lost much of their sediment load due to melting of the ice in a progressively warmer climate. The southernmost latitude studied (37°N) may be close to the southeastern extension of iceberg transport during Heinrich events.

Beschreibung: Polar and subpolar planktic foraminifera and the stable oxygen and carbon isotopes of Neogloboqllndrina pachyderma (s) from the Nordic seas are analyzed for the time period since oxygen isotope Stage 12, with special emphasis on interglacial time slices Stages 11,5e (Eeinian), and 1 (Holocene). A comparison of relative ("/I,) and absolute test concentratioi~sf rom two different size fractions reveals a complex downcore pattern for the morphogroup N. pnclzyderma. Ratios of small-sized N. pacllyderr?ln (s) to N. ~vrclzyderrrla (d) vary between Stage 11, the Eemian and the Holocene, due to changes ill test concentrations of N. pachydernla (s) only. As revealed in the downcore records, both coiling varieties of N, paclzydcri7zn are somehow related to each other, but the use of percent data as surface water mass proxy appears to be limited. The most doininant subpolar species, Elrborotalitn qtlinqt~eloba and Globigerinn bulloides, mainly occurred during the Holocene, the Eemian, and Stage 11. Both species are inversely related to N. pnch!jder17za (s) in that their abundai~ces steadily increased during all three interglacials. During these times, C. blllloill~s remained always restricted to the eastern area of the Nordic seas with dominant Atlantic water masses. In contrast T. qutnqllelobn exhibited a much wider distributional pattern. From stable isotopes and faunal variability it is inferred that the entire Nordic seas was covered by sea-ice during the cold seasons in Stage 11 resulting in both, highest test concentrations of N. pnchyderma (s) and highest 613C values observed tluoughout the past 450 ky. For the last two interglacials, oxygen isotope values and test coi~centrationsof T. q~li~zquelobinad icate that warmer surface waters must have prevailed in the western Iceland Sea in the Eeinian compared with any time during the Holocene time interval.

Beschreibung: Agglutinated foraminifers from 4 box cores spanning the past ca. 140 years (maximum) taken from the southern flank of the Skagerrak (NE North Sea) were studied. Fourtyseven species were identified, among them Liebusella goesi, Eggerelloides spp., Rhabdammina discreta, and Haplophragmoides bradyi are the most common. The two more westerly locations reveal significantly higher amounts of agglutinated foraminifers, which may be caused by a better supply of suitable food provided by east headed bottom currents. Extremely high sedimentation rates and a higher degree of pollution suggest environmental stress that may be one reason for lower amounts of agglutinated foraminifers at the two more easterly stations close to the Skagerrak deep. Increasing numbers of specimens within the present century suggests a combination of instability of the tests and ecological controls.

Beschreibung: Ocean Drilling Program (ODP) Leg 156 revisited the northern Barbados Ridge, where the previous Deep Sea Drilling Program Leg 78A and ODP Leg 110 studied the frontal part of this accretionary prism. Drilling and logging-while-drilling at Sites 947, 948, and 949 successfully identified major thrust faults and the décollement, which was the target of several downhole experiments. Two of the eight holes drilled were equipped with borehole observatories that will monitor temperature, pressure, and fluid flow over the next years. Coring at Hole 948C recovered 180 m of sediment, centered around the décollement, which was positively identified based on structural information. The aim of this study is the evaluation of the possible correlation of preferred orientation of acoustic properties and the direction of maximum compressive strain in the frontal part of the accretionary prism. For this purpose, shipboard P-wave velocities from Holes 948C and 949B were reoriented. This information was then used to compare the directional properties of accreted and subducted sediments. In Hole 948C, lowest transverse velocities (Tmin ) were observed to be consistently oriented perpendicular to the maximum horizontal compressive stress, believed to be parallel to the convergence vector. In the underthrust domain of Hole 948C, several preferred orientations for Tmin were detected, but no correlation with the geotectonic reference frame could be identified. Acoustic anisotropy does not show a comparable pattern in Hole 948C. It is concluded that the observed directional dependence of P-wave velocity in the accreted sediment domain in Hole 948B is the result of moderate to steeply inclined bedding, although this conclusion can not adequately be tested due to the lack of corrected structural data.

Beschreibung: Low-gradient flow tests and one-dimensional consolidation tests were performed on four samples from Ocean Drilling Program (ODP) Leg 156, northern Barbados Ridge, Hole 949B, to provide direct as well as indirect measures of permeability and stress history. All samples tested show a significant degree of underconsolidation, with overconsolidation ratio (OCR) values decreasing with depth from 0.4 to 0.2 to 0.1. These low ratios were used to approximate the excess pore pressures within the accreted sediment and the décollement. The largest estimated excess pore-pressure values lie within the interpreted décollement zone at Site 949 and range from 1600 to 1900 kPa. Combining results from this study with previous data from Leg 110, two generalized functions of void ratio vs. hydraulic conductivity for high and low permeability sediments are developed that are characteristic for sediments of low and high smectite content. By applying these functions to the Site 671 (ODP Leg 110) porosity profile, it is possible to demonstrate the occurrence of a zone of low permeability immediately above the décollement. This is consistent with the concept that low permeability sediments will develop higher excess pore pressures, and therefore, are more susceptible to shear failure.

Beschreibung: Benthic foraminiferal assemblage patterns in Core PS 1246-2 from the Iceland Plateau are examined as they relate to annual productivity and seasonal productivity changes during the Late Pleistocene glacial (23,000-11,000 yrs B.P.), Younger Dryas cool period (11,000-10,000 yrs B.P.) and Holocene (10,000-2,900 yrs B.P.). Abundance fluctuations of Cibicidoides wuellerstorji, a suspension-feeder, are used as the proxy for annual productivity, while fluctuations of the phytodetritus-exploiting species Epistoininclln r ~ i p r a E, ponides tlinzid~illisa nd GloDocossidlrliiia strbglobosa are used as the indicators of seasonal productivity. These records show seasonal productivity began to increase around 22,500 yrs B.P. and experienced three subsequent peaks in the glacial, while annual productivity increased around 16,000 yrs B.P. and shows only one peak in the glacial. The Younger Dryas shows a decrease in both seasonal and annual productivity records. Seasonal productivity in the early Holocene is much higher than during the glacial, yet appears more extreme. The Holocene record of annualproductivity continues to show a strong general increase in intensity.

Beschreibung: Quenched tholeiitic glasses and glassy rims of tholeiitic lava flows and pillow lavas from the neovolcanic rift zone on Iceland (Reykjanes and Hengill fissure swarms) contain olivine phenocrysts (Fo87–91) with abundant primary glass inclusions. These inclusions and host glasses were analyzed by ion microprobe for boron concentrations and isotopic compositions. Inclusions are believed to represent primary or near-primary mantle melts that have not been modified at shallow levels. Boron concentrations and B/K ratios in these melt inclusions are highly variable (0.18–1.35 ppm B, B/K = 2.8 × 10−4−6.1 × 10−3), whereas their δ11B values are nearly constant (−11.3, Full-size image (〈1 K)). This indicates that the Icelandic mantle is likely to have a constant boron isotope composition similar to that previously proposed for the primitive mantle (Full-size image (〈1 K)). The Hengill host glasses are characterized by low concentrations of B (0.26–0.42 ppm) and δ11B values similar to melt inclusions (−11.3, Full-size image (〈1 K)). In contrast, the Reykjanes host glasses have higher δ11B values (∼ −3‰) at the same relatively low concentrations of B (0.43–0.44 ppm), which are likely to be due to interactions of the ascending magmas with the crustal rocks hydrothermally altered at low temperatures by seawater-derived fluids. Boron concentrations and B/K ratios in melt inclusions and matrix glasses correlate with TiO2, K2O and P2O5 contents, and La/Sm)n ratios. Boron contents recalculated on the basis of melt inclusion compositions for the Icelandic mantle are slightly different for the Reykjanes and Hengill areas (0.21, 1σn ± 0.05 and 0.13, 1σn ± 0.03 ppm B, respectively). This is likely to reflect the presence of zones within the Icelandic mantle variously enriched and/or depleted in boron of similar isotopic composition.

Beschreibung: The climate of the Holocene is not well suited to be the baseline for the climate of the planet. It is an interglacial, a state typical of only 10% of the past few million years. It is a time of relative sea-level stability after a rapid 130-m rise from the lowstand during the last glacial maximum. Physical geologic processes are operating at unusual rates and much of the geochemical system is not in a steady state. During most of the Phanerozoic there have been no continental ice sheets on the earth, and the planet’s meridional temperature gradient has been much less than it is presently. Major factors influencing climate are insolation, greenhouse gases, paleogeography, and vegetation; the first two are discussed in this paper. Changes in the earth’s orbital parameters affect the amount of radiation received from the sun at different latitudes over the course of the year. During the last climate cycle, the waxing and waning of the northern hemisphere continental ice sheets closely followed the changes in summer insolation at the latitude of the northern hemisphere polar circle. The overall intensity of insolation in the northern hemisphere is governed by the precession of the earth’s axis of rotation, and the precession and ellipticity of the earth’s orbit. At the polar circle a meridional minimum of summer insolation becomes alternately more and less pronounced as the obliquity of the earth’s axis of rotation changes. Feedback processes amplify the insolation signal. Greenhouse gases (H2O, CO2, CH4, CFCs) modulate the insolation-driven climate. The atmospheric content of CO2 during the last glacial maximum was approximately 30% less than during the present interglacial. A variety of possible causes for this change have been postulated. The present burning of fossil fuels, deforestation, and cement manufacture since the beginning of the industrial revolution have added CO2 to the atmosphere when its content due to glacial-interglacial variation was already at a maximum. Anthropogenic activity has increased the CO2 content of the atmosphere to 130% of its previous Holocene level, probably higher than at any time during the past few million years. During the Late Cretaceous the atmospheric CO2 content was probably about four times that of the present, the level to which it may rise at the end of the next century. The results of a Campanian (80 Ma) climate simulation suggest that the positive feedback between CO2 and another important greenhouse gas, H2O, raised the earth’s temperature to a level where latent heat transport became much more significant than it is presently, and operated efficiently at all latitudes. Atmospheric high- and low-pressure systems were as much the result of variations in the vapor content of the air as of temperature differences. In our present state of knowledge, future climate change is unpredictable because by adding CO2 to the atmosphere we are forcing the climate toward a “greenhouse” mode when it is accustomed to moving between the glacial–interglacial “icehouse” states that reflect the waxing and waning of ice sheets. At the same time we are replacing freely transpiring C3 plants with water-conserving C4 plants, producing a global vegetation complex that has no past analog. The past climates of the earth cannot be used as a direct guide to what may occur in the future. To understand what may happen in the future we must learn about the first principles of physics and chemistry related to the earth’s system. The fundamental mechanisms of the climate system are best explored in simulations of the earth’s ancient extreme climates.

Beschreibung: Iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of Fe. A combination of various leaching agents (1 M HCI, dithionite buffered in citrate/acetic acid, HF/H2SO4, acetic Cr(II)) was applied to sediment and extracted more than 80% of total Fe. Subsequent Fe species determination defined specific mineral fractions that are available for Fe reduction and fractions formed as products of Fe diagenesis. To determine the Fe speciation of (sheet) silicates we explored an extraction procedure (HF/H2SO4) and verified the procedure by application to standard rocks. Variations of Fe speciation of (sheet) silicates reflect the possible formation of Fe-bearing silicates in near surface sediments. The same fraction indicates a change in the primary input at greater depth, which is supported by other parameters. The Fe(II)/ Fe(III) -ratio of total sediment determined by extractions was compared with Mössbauer-spectroscopy ] at room temperature and showed agreement within 10%. M6ssbauer-spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite, supporting the importance of microenvironments during mineral formation. The occurrence of other Fe(II) bearing minerals such as ankerite (Ca-, Fe-, Mg-carbonate) can be presumed but remains speculative.

Beschreibung: The North Atlantic is one of the most important oceans for virtually any subject of scientific interest. Geophysicists investigating rifting and plate tectonics, as well as marine geologists and marine micropaleontologists, appreciate that even the birth of the North Atlantic is still recorded in the form of sediments in t l~ea stern- and westernmost parts of the equatorial North Atlantic. Like all other oceans, much of the geological history of the North Atlantic has been reconstructed due to the success of the Ocean Drilling Program (ODP) and its predecessor the Deep Sea Drilling Project (DSDP). Since the launch of the drilling programs, many cores have recovered sediments, including subsediment crustal structures, that led to the understanding of the evolution of (not only!) the North Atlantic Ocean, its paleoceanography and the Eartll's climatic development through the past 155 million years.

Beschreibung: Oxygen isotope analyses of marine diatoms were performed in two independent ways. Stepwise fluorination of hydrous opal-A results in plateau δ180 values representing the isotopic composition of the silica frame oxygen. A method of controlled isotope exchange before silica dehydration also produces reliable results, although the exchangeability of the silica was variable. Consequently, a calibration of the isotope exchange method using the results from stepwise fluorination experiments is very useful (and sometimes essential) in order to select a water vapor of an appropriate isotopic composition to be used for equilibration. Sediment diatom samples Ethmodiscus rex and Thalassiothrix longissima from the Antarctic and the North Atlantic Ocean, respectively, show strong 180 enrichments of 46.8 and 44.1‰, which are caused by large isotope fractionation occurring at the low temperature prevailing during silica-water isotope exchange reactions. However, phytoplankton samples from surface waters of the Norwegian-Greenland Sea and the Bellingshausen Sea (Antarctica) have δ180 values between 30.4 and 35.0‰. Thus, the true silica-water isotopic fractionation is approximately 3 to 10‰ lower than the temperature-dependent silica-water equilibrium published in the literature for sedimentary diatoms. Our results indicate that successive isotope exchange reactions of diatomaceous silica with ambient seawater and/or pore water determine the isotope values of diatoms in sediments.

Beschreibung: The effect of variable CO2 concentrations on the elemental composition (C:N:P) of marine diatoms was investigated in 2 strains of Skeletonema costatum (Grev.) Cleve. Five or 6 concentrations of dissolved molecular carbon dioxide [CO2 (aq)], ranging from 0.5 to 39 µmol l-1, were applied in dilute batch cultures. In both strains, elemental ratios were clearly dependent on [CO2 (aq)]. With decreasing CO2 concentrations, a decline in C:P and N:P and an increase in C:N was observed. The close correlation between C:P or N:P and [CO2 (aq)] corresponded to a ca 45 to 65% decrease in elemental ratios from highest (〉=30 µmol l-1) to lowest (ca 1 µmol l-1) CO2 concentrations. C:N at low [CO2 (aq)] was up to 24% higher than at high [CO2 (aq)]. To date, the elemental composition of marine phytoplankton has been considered to be independent of CO2 availability. If dependency of the C:N:P ratio on [CO2 (aq)] proves to be a general phenomenon in marine phytoplankton, changes in the elemental composition may be expected in response to the currently observed increase in partial pressure of atmospheric CO2.

Beschreibung: In situ oxygen fluxes were measured at vent sites in the Aleutian trench at a water depth of almost 5000 m using a TV-guided benthic flux chamber. The flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off Alaska. Porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide, methane, and ammonia. The reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence. The tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3.4 ± 0.5 m yr−1. A model was used to quantify the transport of silica, Ca2+, and sulfate via diffusion, advection, and bioirrigation through the surface sediments of a vent site. A nonlocal mixing coefficient of 20–30 yr−1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near-surface sediments and across the sediment-water interface is dominated by the activity of the vent fauna. Sulfate-containing oceanic bottom water and methane-rich vent fluids were mixed below the clam colony to produce sulfide and a CaCO3 precipitate. The vent biota shape their immediate environment and control the sediment-water exchange and the benthic fluxes at vent sites. The oxygen consumption at vent sites is a major sink for oxygen at the study area.

Beschreibung: There has been a widespread increase in the reporting of harmful and ‘nuisance’ algal blooms in the coastal ocean over the past few decades. On the global scale this is suspected to be a consequence of coastal eutrophication, however, on a case-by-case basis there is usually insufficient evidence to discriminate between the effects of human and natural causal factors. Intense blooms of the ‘Brown Tide’ unicellular algae (Aureococcus anophagefferens) have occurred sporadically since 1985 in coastal waters of Eastern Long Island and have devastated the local commercial scallop fishery. Analysis of an 11-year time-series dataset from this region indicates that bloom intensity is correlated with higher salinities and inversely correlated with the discharge of groundwater. Laboratory and field studies suggest that whereas salinity is unlikely to represent a direct physiological control on Brown Tide blooms, the addition of inorganic nitrogen tends to inhibit Brown Tide blooms. Budget calculations indicate that the inorganic nitrogen supply from groundwater is 1–2 orders of magnitude higher than any other external source of nitrogen for this ecosystem. Biweekly time series data collected in 1995 demonstrate that Brown Tide blooms utilize dissolved organic nitrogen (DON) for growth, as evidenced by a large decrease in DON parallel with an increase in cell abundance. On an interannual basis, bloom intensity was also positively correlated with mean DON concentrations. We hypothesize that bloom initiation is regulated by the relative supply of inorganic and organic nitrogen, determined to a large extent by temporal variability in groundwater flow. The 1980s and 1990s were characterized by exceptionally high and interannually variable groundwater discharge, associated with a large-scale climate shift over the North Atlantic. This, coupled with the time-lagged discharge of groundwater with high nitrate concentrations resulting from increased fertilizer use and population increase during the 1960s and 1970s, may have been a key factor in the initiation of Brown Tide blooms in 1985

Beschreibung: Indian Central Water (ICW) and Subantarctic Mode Water (SAMW) are the two major sources for the ventilation of the permanent thermocline in the Indian Ocean. ICW is formed by subduction in the region of negative wind stress curl, while SAMW is formed by convective overturning at the Subantarctic Front. SAMW contributes to the depth range of ICW, but is not easily identified, because most hydrographic properties (temperature, salinity and nutrients) of SAMW do not differ much from those of ICW. This study identifies ICW and SAMW in a zonal section near 32°S and evaluates the relative importance of convection vs. subduction for the ventilation process. Oxygen and nutrient data from the eastern part (50–114°E) of WOCE section 15 are used with temperature and salinity to determine water mass fractions of subducted ICW and of SAMW from water mass mixing analysis. The individual age fields of the two water mass components are then derived from a combination of the fractions obtained with a linear oxygen/CFC mixing model. Unlike earlier studies, which derive an uncalibrated apparent age, our results express water mass age in true units of time (years). The core of the SAMW near 114°E is about 5 years old, while the core of the subducted ICW (at 60–80°E) shows an increase of age with depth, in agreement with the subduction process. ICW moves eastward with the South Indian Current, reaching an age of 35 years at 114°E. SAMW spreads westward against the mean flow through turbulent diffusion, reaching an age of 25 years at 50°E.

Beschreibung: A combined 3-D physical oceanographic model and a field sampling program was performed in July and August 1994 to investigate the potential drift of larval Baltic cod from the center of spawning effort in the Bornholm Basin, Baltic Sea. The goal of this exercise was to predict the drift trajectories of cod larvae in the Bornholm Basin, thereby aiding in the development of future sampling programs as well as the identification of processes influencing larval retention/dispersion in the Bornholm Basin. Distributions of variables (T, S and larval distribution) were obtained utilizing a three-dimensional eddy-resolving baroclinic model of the Baltic Sea based on the Bryan-Cox-Semtner code. Larval drift was simulated by the incorporation of a passive tracer into the model utilized to represent individual cod larvae. Additionally, simulated Lagrangian drift trajectories are presented. For model purposes, initial fields of temperature, salinity and cod larvae concentration for the Bornholm Basin were constructed by objective analysis using observations taken during a research survey in early July, 1994. Outside the Bornholm Basin generalized hydrographic features of the Baltic Sea were utilized with the baroclinic model forced by wind data for the whole Baltic taken from the Europa-Modell (EM) of the German weather service, Offenbach. Verification of simulations was performed by comparison with field measurements of hydrographic variables and ADCP derived current measurements taken during the surveys. In general, most of the hydrographic features observed during the second research cruise are correctly simulated, with variations mainly attributed to the prescribed initial conditions outside the Bornholm Basin. Results from larval sampling during the second cruise could not entirely confirm the modeled larval distributions due to the low numbers of larvae captured. However, the modeled results based on the agreement of the flow fields and hydrographic properties with observed features suggest that predictions of larval distributions can be made with a high degree of confidence if appropriate larval behaviours are included in the simulations.

Beschreibung: The dating of polymetamorphic rocks with the U-Pb zircon method often results in discordant data. Thus a new technique combining cathodoluminescence imaging (CL) and thermal ion mass spectrometry (TIMS) measurements was developed. Cathodoluntinescence-controlled UPb dating (CLC-method) works with bisected zircons and was successfully applied to the multistage S-type granitoids of the Swiss Silvretta nappe. CLC-method enables the resolution of the different anatectic events and later major overprints (Cambrian, Ordovician, Silurian) and gives information about the protolith (Archaean) of the investigated gneisses. This is achieved by conventional UPb dating of selected grains, recovered from the SEM (scanning electron microscope) mounts after cathodoluminescence (CL) imaging. Applying this new combination of two established techniques yields geologically meaningful UPb zircon ages even for complex polymetamorphic rocks.

Beschreibung: Recent studies have indicated that drifting Arctic sea ice plays an important role in the redistribution of sediments and contaminants. Here we present a method to reconstruct the backward trajectory of sea ice from its sampling location in the Eurasian Arctic to its possible site of origin on the shelf, based on historical drift data from the International Arctic Buoy Program. This method is verified by showing that origins derived from the backward trajectories are generally consistent with other indicators, such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions. The trajectories are then used to identify regions where sediment‐laden ice is exported to the Transpolar Drift Stream: from the New Siberian Islands and the Central Kara Plateau. Calculation of forward trajectories shows that the Kara Sea is a major contributor of ice to the Barents Sea and the southern limb of the Transpolar Drift Stream.

Beschreibung: Two seasonal hydrographic data sets, including temperature, salinity, dissolved oxygen, and nutrients, are used in a mixing model which combines cluster analysis with optimum multiparameter analysis to determine the spreading and mixing of the thermocline waters in the Indian Ocean. The mixing model comprises a system of four major source water masses, which were identified in the thermocline through cluster analysis. They are Indian Central Water (ICW), North Indian Central Water (NICW) interpreted as aged ICW, Australasian Mediterranean Water (AAMW), and Red Sea Water (RSW)/Persian Gulf Water (PGW). The mixing ratios of these water masses are quantified and mapped on four isopycnal surfaces which span the thermocline from 150 to 600 m in the northern Indian Ocean, on two meridional sections along 60°E and 90°E, and on two zonal sections along 10°S and 6°N. The mixing ratios and pathways of the thermocline water masses show large seasonal variations, particularly in the upper 400–500 m of the thermocline. The most prominent signal of seasonal variation occurs in the Somali Current, the western boundary current, which appears only during the SW (summer) monsoon. The northward spreading of ICW into the equatorial and northern Indian Ocean is by way of the Somali Current centered at 300–400 m on the σθ=26.7 isopycnal surface during the summer monsoon and of the Equatorial Countercurrent during the NE (winter) monsoon. More ICW carried into the northern Indian Ocean during the summer monsoon is seen clearly in the zonal section along 6°N. NICW spreads southward through the western Indian Ocean and is stronger during the winter monsoon. AAMW appears in both seasons but is slightly stronger during the summer in the upper thermocline. The westward flow of AAMW is by way of the South Equatorial Current and slightly bends to the north on the σθ=26.7 isopycnal surface during the summer monsoon, indicative of its contribution to the western boundary current. Outflow of RSW/PGW seems effectively blocked by the continuation of strong northward jet of the Somali Current along the western Arabian Sea during the summer, giving a rather small contribution of only up to 20% in the Arabian Sea. A schematic summer and winter thermocline circulation emerges from this study. Both hydrography and water ‐ mass mixing ratios suggest that the contribution of the water from the South Indian Ocean and from the Indo‐Pacific through flow controls the circulation and ventilation in the western boundary region during the summer. However, during the winter the water is carried into the eastern boundary by the Equatorial Countercurrent and leaks into the eastern Bay of Bengal, from where the water is advected into the northwestern Indian Ocean by the North Equatorial Current. The so‐called East Madagascar Current as a southward flow occurs only during the summer, as is suggested by both hydrography and water‐mass mixing patterns from this paper. During the winter (austral summer) the current seems reversal to a northward flow along east of Madagascar, somewhat symmetrical to the Somali Current in the north.

Beschreibung: Modem reefs in the Red Sea exhibit different controls on their formation. The majority of the reefs belong to the fringing type. These reefs grow close to the mainland and are abscnt in wadi mouths. Their arrangement and orientation are strongly controlled hy the siliciclastic input from the hinterland. In addition, discharge events due to ephemeral precipitation may cause local but serious damage of the reef-building assemblages. However, the gene;al pattern of reef arrangement follows the morphology of the coastline, which itself portrays the tectonic framework of the Red Sea. Barrier reefs and even atolls also occur, predominantly in the central and southern part of this young ocean. Both reef types show a strong control by the tectonic framework of riftrelated origin. The outlines of the reef crest and the orientation' of the foreslopes follow the tectonic pattern. Spectacular drop-ofTs are widespread and represent predominantly fault planes of horsts and graben structures parallel to the rift. Furthermore rift-related salt diapirism occurs, which influences reef shapes, indicated by circular and semicircular outlines. Besides these controls, sea-level changes are a trigger as weil. They are documented in onshore and ofsf hore terraces and their prescnt-day position can be attributed to the last glacial-interglacial cycle. These difefrent controls along with the two major reef types and their typical zonation patterns are discussed briefly.

Beschreibung: Particle flux data have been collated from the literature representing most areas of the open ocean to determine regional trends in deep water flux and its seasonal variability. Organic carbon flux data normalised to a depth of 2000 m exhibits a range of an order of magnitude in areas outside the polar domains (0.38 to 4.2 g/m2/y). In polar regions the range is wider (0.01–5.9 g/m2/y). Latitudinal trends are not apparent for most components of the flux although calcite flux exhibits a poleward decrease. Limited data from polar regions show fluxes of opaline silica not significantly higher than elsewhere. The variability of flux over annual cycles was calculated and expressed as a Flux Stability Index (FSI) and the relationship between this and vertical flux of material examined. Somewhat surprisingly there is no significant relationship between FSI and fluxes of dry mass, organic carbon, inorganic carbon or opaline silica. At each site, net annual primary production was determined using published satellite derived estimates. There is a negative but weak relationship between FSI and the proportion of primary production exported to 2000 m (e2000 ratio). The most variable of the non-polar environments export to 2000 m about twice as much of the primary production as the most stable ones. Polar environments have very low e2000 ratios with no apparent relationship to FSI. At primary production levels below 200 g C/m2/y there is a positive correlation between production and organic carbon flux at 2000 m but above this level, flux remains constant at about 3.5g C/m2/y. A curve derived to describe this relationship was applied to estimates of annual primary production in each of 34 of the open ocean biogeochemical provinces proposed by Longhurst et al. (1995). Globally, open ocean flux of organic carbon at 2000 m is 0.34 Gt/yr which is 1% of the total net primary production in these regions. This flux is nearly equally divided between the Atlantic, Pacific and Southern Oceans. The Indian and Arctic oceans between them only contribute 5% to the total. The eight planktonic climatological categories proposed by Longhurst (1995) provide a most useful means of examining the data on flux and its variability. A characteristic level of FSI was found in each category with highest levels in the tropics and lowest levels in the Antarctic. There is also a characteristic level of export ratio in each category with the highest in monsoonal environments (1.7%) and the lowest in Antarctica (0.1%)

Beschreibung: Extensive investigations of sedimentary barium were performed in the southern South Atlantic in order to assess the reliability of the barium signal in Antarctic sediments as a proxy for paleoproductivity. Maximum accumulation rates of excess barium were calculated for the Antarctic zone south of the polar front where silica accumulates at high rates. The correspondence between barium and opal supports the applicability of barium as a proxy for productivity. Within the Antarctic zone north of today's average sea ice maximum, interglacial vertical rain rates of excess barium are high, with a maximum occurring during the last deglaciation and early Holocene and during oxygen isotope chronozone 5.5. During these periods, the maximum silica accumulation was supposedly located south of the polar front. Glacial paleoproductivity, instead, was low within the Antarctic zone. North of the polar front, significantly higher barium accumulation occurs during glacial times. The vertical rain rates, however, are as high as in the glacial Antarctic zone. Therefore there was no evidence for an increased productivity in the glacial Southern Ocean.

Beschreibung: A neural network is used to calculate the longwave net radiation (Lnet) at the sea surface from measurements of the Special Sensor Microwave/Imager (SSM/I). The neural network applied in this study is able to account largely for the nonlinearity between Lnet and the satellite-measured brightness temperatures (TB). The algorithm can be applied for instantaneous measurements over oceanic regions with the area extent of satellite passive microwave observations (30–60 km in diameter). Comparing with a linear regression method the neural network reduces the standard error for Lnet from 17 to 5 W m−2 when applied to model results. For clear-sky cases, a good agreement with an error of less than 5 W m−2 for Lnet between calculations from SSM/I observations and pyrgeometer measurements on the German research vessel Poseidon during the International Cirrus Experiment (ICE) 1989 is obtained. For cloudy cases, the comparison is problematic due to the inhomogenities of clouds and the low and different spatial resolutions of the SSM/I data. Global monthly mean values of Lnet for October 1989 are computed and compared to other sources. Differences are observed among the climatological values from previous studies by H.-J. Isemer and L. Hasse, the climatological values from R. Lindau and L. Hasse, the values of W. L. Darnell et al., and results from this study. Some structures of Lnet are similar for results from W. L. Darnell et al. and the present authors. The differences between both results are generally less than 15 W m−2. Over the North Atlantic Ocean the authors found a poleward increase for Lnet, which is contrary to the results of H.-J. Isemer and L. Hasse.

Beschreibung: Since large, homogeneous dielectric particles have positive asymmetry parameters even when they are densely packed, it has been hypothesized that negative asymmetry parameters retrieved with Hapke's phenomenological model of bidirectional reflectance result from a complicated internal structure of planetary regolith particles. This paper tests that hypothesis by theoretically computing asymmetry parameters for isolated and densely packed composite spherical particles with size typical of regolith grains. It is assumed that the wavelength of the scattered light is much smaller than the particle size, and that particles are filled with large numbers of small inclusions. The computations show that it is essentially impossible to make asymmetry parameters of planetary regolith particles even slightly negative by filling the particles with large numbers of internal inclusions in the form of voids and/or grains with a refractive index substantially different from that of the host medium. Asymmetry parameters are positive even for densely packed composite particles with no internal absorption and extreme values of the internal scattering coefficient. Furthermore, they are sharply increased by even modest absorption inside composite particles, by reducing the refractive index contrast between the inclusions and the host particles, and/or by decreasing the packing density. Thus, the negative asymmetry parameters retrieved with Hapke's model need another explanation rather than assuming that they are real and are the result of a complicated internal structure of regolith particles. Besides the opposition-effect term, Hapke's model is nothing more than an approximate solution of the radiative transfer equation which inherently violates the energy conservation law. Therefore, the negative asymmetry parameters are likely to be numerical artefacts resulting from the approximations made in the model.

Beschreibung: Oceanic and atmospheric circulation patterns varied considerably during the Tertiary and Quaternary and influenced the geochemical cycles of elements in seawater. We report the first resolution lead and neodymium isotopic record of such changes at a high time resolution in two depths profiles from a hydrogenous FeMn crust. The crust, Va13-2, is located in the central Pacific (146°W, 9°25′N, 4830 m) and has previously been dated by 230Th and 10Be. The first profile was drilled with a sample time resolution of ∼3 kyr and allows evaluation of short-term changes to lead and neodymium sources to central Pacific seawater over the last 400 kyr (marine δ18O stages 2 to 11). Longer-term changes were monitored at lower time resolution in a second profile to an age of 10 Ma. Short-term variations in lead and neodymium isotope ratios are resolved in the high resolution profile (0 to 400 kyr). Superimposed on the short-term variations is a secular decrease in Full-size image (〈1 K) ratios beginning at ∼130 kyr in marine δ18O stage 5, implying a change in the lead sources to the central Pacific. Lead and neodymium isotopic compositions indicate an increased influence from Central American eolian sources to Pacific seawater at this time. Lead isotopes are found to be statistically more variable during interglacial than glacial periods. These observations are supported by the greater eolian dust fluxes found in sediment cores from the equatorial Pacific during interglacial stages. The most important paleoceanographic event of the last 10 Ma to affect Pacific seawater was the closure of the Panama gateway. Changes in lead and neodymium isotopes in Val3-2 during the last 10 Ma occurred along with gradual closure of the Panama straits. However, these changes did not occur in tandem: while neodymium isotope ratios increase between 10 and 8 Ma, lead isotope ratios remain constant. In contrast, the period 7 to 1 Ma is marked by a secular increase in lead isotope ratios but nearly constant neodymium. These changes are consistent with a source of radiogenic lead and neodymium conveyed by the Circumpolar Current into the Pacific, rather than by the Panama gateway, and involve 20 to 40% Southern Component Water (SCW) input of lead and neodymium. Modelling of lead and neodymium isotopic mixing between the different water masses involved in generating Pacific deep waters lead us to the following conclusions: (1) Small variations in the strength and composition of North Atlantic Deep Water (NADW) have a relatively minor effect on the amounts of lead and neodymium from SCW contributing to the Pacific and (2) an enhanced SCW flow with an open isthmus of Panama, as suggested by General Circulation Models (GCM), requires a corresponding reduction in NADW Pb and Nd contributions to SCW. The general agreement between the isotopic compositions of surface layers of Mn nodules, integrated over such long time intervals, and those of present-day bottom waters at their respective locations show that the present-day ocean circulation pattern has dominated through the Pleistocene. Our study of Mn crust Va13-2 shows that shorter-term changes in lead and neodymium isotope ratios can be resolved, provided that such crusts are sampled at an appropriate time resolution.

Beschreibung: Precise strontium isotope ratios, combined with chemical analyses and sedimentological information, are used to monitor the water sources and the evolution of the Dead Sea and its late Pleistocene precursor, Lake Lisan (70-18 kyr B.P.). The materials analyzed include bulk aragonite, water-leached soluble salts, and residual aragonite and gypsum from the Lisan Formation in the Perazim Valley (near the SW shore of the Dead Sea). The residual aragonite and the associated soluble salts display systematic fluctuations in 17Sr86Sr ratios between 0.70803 and 0.70806 and from 0.70805 to 0.70807, respectively. In individual soluble salt-residual aragonite pairs, the soluble salt displays a higher 87Sr86Sr ratio. Gypsum samples yield 17Sr86Sr ratios similar to the soluble salts from adjacent layers in the section. This shows that, in individual samples, the source of Sr in aragonite was distinct from that in soluble salts and the gypsum. The sterility of the Lisan sediments, their strictly nonbioturbated fine lamination, and their high content of chloride salts indicate that Lake Lisan was a saline, or even hypersaline water body. In the absence of alternative sources of HCO3− and S042− the abundance of primary aragonite and gypsum in the Lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake, resulting in a density stratification of this water body. The history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples, respectively. Whereas the bicarbonate and much of the Ca2+ required for aragonite crystallization were supplied by the freshwater, the complementary Ca2+ (and Sr 2+) were added by the lower brine. The upper water layer of Lake Lisan acted as a SO42− capacitor during the lake's rise periods. It was removed therefrom, as prominent gypsum beds, upon climatic-induced (drier period) mixing or even complete overturn of the lake. The evolution of Lake Lisan took place between two distinct modes. The first was characterized by an extensive supply of freshwater and resulted in a rise of the lake's level, a (density) layered structure, and precipitation of aragonite. The second mode was marked by a diminishing freshwater input, resulting in mixing or complete overturn of its water, and precipitation of gypsum. These two modes reflect the climatic evolution of the region in the late Pleistocene which fluctuated between drier and wetter periods. The transition to the Holocene is accompanied by the dry up of Lake Lisan and its contraction to the present Dead Sea.

Beschreibung: We deployed CO2 and O2 sensors on the U.S. continental shelf off Cape Hatteras, North Carolina, during late summer 1994. A continuous 32‐d gas record was obtained at 20 m in 25 m of water, below the thermocline for most of the period. Analysis of the correlation between CO2 and O2 indicates that biological and advective processes dominated the gas variability, with small or insignificant fluxes due to air–sea exchange, vertical eddy diffusion, and carbonate dissolution or formation. The observed O2 : CO2 correlation was 1.39, within the range predicted for the photosynthetic quotient. Photosynthesis and respiration appeared to be tightly coupled, resulting in no net community production in these waters during the late summer. It is evident from these results that the combination of mooring‐based CO2 and O2 measurements will be a powerful tool for studying the marine carbon cycle.

Beschreibung: Iridium enrichments, at or close to the K/T boundary, are often cited as evidence for impacts of cosmic bodies or volcanic events, or both, that resulted in mass extinctions. A third possible explanation for the high Ir concentrations, that the enrichments were caused by the cosmic micrometeorite flux during times of slow Sediment accumulation, has generally been rejected. In this study we examine the Ir/Au ratios and conclude that they may indicate enrichment of siderophile elements by slow sedimentation. In addition, the concept of slow sedimentation at the K/T boundary is consistent with many aspects of the K/T boundary research such as the gradual decline of the species before the major extinction level and recent reports of faunal transitions from Cretaceous to Tertiary without sudden extinctions, hiatuses or Ir anomalies.