ALBERT

Description: Colonization structures of the large parasitic foraminifer Hyrrokkin sarcophaga Cedhagen, 1994 on Lophelia pertusa, Acesta excavata and Delectopecten vitreus are described from a deep-water coral reef mound on the mid-Norwegian shelf at 240 to 300 m water depth. Hyrrokkin sarcophaga is the only epibiont which is capable of attaching itself on the soft tissue-protected coral skeleton where it tends to form clusters of 3 to 8 specimens close to the tentacles of Lophelia. The foraminifer excavates a pit up to 1.5 mm deep and etches a straight channel through the skeleton of the host which ends within the soft tissue. In contrast to Lophelia, infested bivalves show a strong wound repair reaction and seal the etched channels by intense calcification. The etching is only performed by adult specimens. Substrate pitting is considered to improve the attachment strength while boring enables the parasite to secure a persistent nutrient source.

Description: 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.

Description: Sediment cores containing up to twenty-five ash layers were taken at three sites close to Vesterisbanken Seamount in the Greenland Basin. These ash layers imply frequent eruptions of the volcano within the last 60 ka. The eruptions led to airborne transport and volcaniclastic turbidity flows which transported volcanic glassy and crystalline material from the volcano into the surrounding basin. During the eruption and the transport the glass and the crystal particles were mixed. The glasses range in composition between basanites and phonolites/benmoreites with MgO contents of 8 to 0.65%. The glass analyses follow a distinct trend of fractionation suggesting the crystallization of the phases olivine, clinopyroxene, plagioclase, kaersutite, Cr-spinel, Ti-magnetite and apatite. A strong zonation of clinopyroxene and kaersutite phenocrysts implies mixing processes in the magma system although the liquid compositions do not lie on mixing trends. A geochemical study of the bulk ashes shows that some ash layers possess distinct chemical compositions. The ashes are more evolved than the lavas of the volcano, suggesting fractionation of liquid from crystallized material during the eruption or transport of the ashes. Sixteen layers are statistically combined into four groups, of which several can be correlated from core to core reflecting individual eruptive events.

Description: Stable isotope records of demosponges from the Caribbean and Coral Sea are described for the purpose of studying the influence of fossil fuel CO2 on the carbon isotopic composition of dissolved inorganic carbon (DIC) in surface water. The slow-growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in δ13CDIC from pre-industrial times (early 19th century) to the present. We observed similar shapes and ranges in δ13C curves measured on Caribbean specimens collected from water depths of 25, 84 and 91 m as well as a specimen collected in shallow waters off New Caledonia. The records reveal a highly significant correlation with atmospheric δ13CCO2. δ13CDIC values for Caribbean and Coral Sea surface waters were calculated using the δ13C sponge records. While δ13C of atmospheric CO2 decreased by about 1.4‰ from the early 19th century to 1990, δ13CDIC of Caribbean and Coral Sea surface waters decreased by 0.9±0.2‰ and 0.7±0.3‰, respectively. No isotopic equilibrium between surface water DIC and atmospheric CO2 was observed, either during the pre-industrial steady state or during the last 100 years. The lower amount of depletion in the surface water δ13CDIC with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water DIC. The lower δ13C decrease in the Coral Sea points to a stronger influence of the subsurface water source compared to the Caribbean.

Description: The record of glacier fluctuations in western Scandinavia, as reconstructed from continental data, has been correlated with records of ice-rafted detritus (IRD) from well-dated sediment cores from the Norwegian Sea covering the past 150,000 yr B.P. The input of IRD into the ocean is used as a proxy for ice sheet advances onto the shelf and, thus, for the calibration of a glaciation curve. The marine results generally support land-based reconstructions of glacier fluctuations and improve the time-control on glacial advances. The Saalian ice sheet decayed very rapidly approximately 125,000 yr B.P. In the Early Weichselian, a minor but significant IRD maximum indicates the presence of icebergs in isotope substage 5b (especially between 95,000 and 83,000 yr B.P.). Reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b. An extensive build-up of inland ice began again during isotope stage 4, but maximum glaciation was reached only in early stage 3 (58,000-53,000 yr B.P.). Marine sediments have minimum carbonate content, indicating strong dilution by lithogenic ice-rafted material. Generally, the IRD accumulation rate was considerably higher in stages 4-2 than in stage 5. A marked peak in IRD accumulation rates from 47,000 to 43,000 yr B.P. correlates well with a second Middle Weichselian ice sheet advance dated by the Laschamp/Olby paleomagnetic event. Minimum ice extent during the Ålesund interstade (38,500-32,500 yr B.P.) and several glacial oscillations during the Late Weichselian are also seen in the IRD record. Of several late Weichselian glacial oscillations on the shelf, at least four correspond to the North Atlantic Heinrich events. Ice sheet behavior was either coupled or linked by external forcing during these events, whereas internal ice sheet mechanisms may account for the noncoherent fluctuations.

Description: Data from sections across the Eurasian Basin of the Arctic Ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the Arctic Ocean and on sources of the deep waters of the Nansen, Amundsen and Makarov basins. Using salinity, H218O, and mass balances we estimate the river-runoff and the sea-ice melt water fractions contained in the upper waters of the Arctic Ocean and infer pathways of the river-runoff signal from the shelf seas across the central Arctic Ocean to Fram Strait. The average mean residence time of the river-runoff fraction contained in the Arctic Ocean halocline is determined to be about 11 to 14 years. Pacific water entering through Bering Strait is traced using silicate and its influence on the halocline waters of the Canadian Basin is estimated. Water column inventories of river-runoff and sea-ice melt water are calculated for a section just north of Fram Strait and implications of these inventories for sea-ice export through Fram Strait are discussed. Comparison of the ratios of shelf water, Atlantic water and the deep waters of the Arctic Ocean indicate that the sources of the deep and bottom waters of the Eurasian Basin are located in the Barents and Kara seas.

Description: Climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the Nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes. Combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice-rafted debris (IRD) allows separation of local and global effects and subdivision of the marine oxygen isotope events 6.2–5.4, which include the last interglaciation, into: (1) a meltwater phase after glacial stage 6, recorded by large amounts of IRD and low foraminiferal abundance, indicating surface water warming; (2) an IRD-free period with high deposition rates of subpolar foraminifera and other CaCO3pelagic components, recognized here as the “full” interglaciation; and (3) a phase with the recurrence of IRD and the demise of subpolar species. Comparison of ice-core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial Holocene were similar. The records show no significantly different variations in the proxy data. In contrast, the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions (Terminations I and II) that preceded these two interglaciations. These suggest that during Termination II the climatic evolution in the Nordic seas was less affected by abrupt changes in ocean–atmosphere circulation than during the last glacial to interglacial transition.

Description: Short-term iron enrichment experiments were carried out with samples collected in areas with different phytoplankton activity in the northern North Sea and northeast Atlantic Ocean in the summer of 1993. The research area was dominated by high numbers of pico-phytoplankton, up to 70,000 ml−1. Maximum chlorophyll a concentrations varied from about 1.0 μg l−1 in a high-reflectance zone (caused by loose coccoliths, remnants from a bloom of Emiliania huxleyi) and about 3.5 μg l−1 in a zone in which the phytoplankton were growing, to about 0.5 μg l−1 in the northeast Atlantic Ocean. From the high-reflectance zone to the northeast Atlantic Ocean, nitrate concentrations increased from 0.5 μM to 6.0 μM. Concentrations of reactive iron in surface water showed an opposite trend and decreased from about 2.6 nM in the high-reflectance zone to 〈1.0 nM in the northeast Atlantic Ocean. In the research area, no signs of true iron deficiency were found, but iron enrichments in the high-reflectance zone, numerically dominated by Synechococcus sp., resulted in increased nitrate uptake. Ammonium uptake was hardly affected. Strong support for the effect of Fe on cell physiology is given by the increase in the f-ratio. Net growth rates of the phytoplankton (changes in cell numbers over 24 h) were almost unchanged. Phytoplankton collected from the northeast Atlantic Ocean, did not show changes in the nitrogen metabolism upon addition of iron. Net growth rates in these incubations were low or negative, with only slightly higher values with additional iron.

Description: Catalytic cathodic stripping voltammetry (CSV) preceded by adsorptive collection of complexes of 1-nitroso-2-napthol (NN) can be used to determine iron in seawater. It is shown here that iron(II) is effectively masked in the presence of 2,2-dipyridyl (Dp) so that iron(III) is measured selectively. The concentration of iron(II) is then calculated as the difference between the concentrations of reactive iron (Fe-R) in the absence and presence of 2 mu M Dp, Fe-R being defined as that which was complexed by 20 mu M NN at pH 6.9 in the presence of 1.8 mM H2O2 and 5 ppm sodium dodecyl sulphate. A 30 min reaction time was allowed for Dp to react with iron(II) in seawater prior to the determination of reactive iron(III) using the same conditions as used for Fe-R. Detection limits of 0.08 nM, 0.077 nM and 0.12 nM were obtained for Fe-R, iron(III) and iron(II), respectively, using a 60 s deposition time. The method was utilised to determine the redox speciation of iron in the northern North Sea. Concentrations of Fe-R ranged between 0.8 and 3.5 nM with nutrient-like depth profiles. Iron(II) was found to be present at concentrations up to 1.2 nM, the highest concentrations occurring in the upper 20 m of the water column.

Description: The widespread view that scleractinian corals in cold and deep waters of high latitudes are slow growing organisms that do not form reefs is challenged by the discovery of a huge coral reef over 13 km in length, 10 to 35 m in height and up to 300 m in width formed by the coral Lophelia pertusa in water depths of 270 to 310 m at 64°N on the Sula Ridge, Mid-Norwegian Shelf. Cruises in 1994, 1995 and manned submersible operations in May 1997 provide data and observations from which the structure and development of the Sula Ridge coral reef have been determined. The Fennoscandian icesheet retreated from the Mid-Norwegian shelf prior to 12,000 years before present and modern oceanographic conditions were established at 8000 years before present. Coral growth since that time has resulted in a large deep-water shelf reef for which recent stable isotopic studies have demonstrated high growth rates for these azooxanthellate cold-water corals. Information on the geometry of deep-water coral reefs and their environmental controls is still fragmentary, controversial and raises issues of conservation in this area of active fishing and oil exploration. This paper reports on the discovery of what is probably one of the largest deep-water coral reefs existing in the northeast Atlantic and indicates that its siting is due to post-glacial structures (iceberg plough marks), events (the second Storegga Slide) and local conditions on the seafloor. Surprisingly, reef accumulation rates on the Sula Ridge are comparable with those measured on tropical coral reefs.

Description: An ultra-violet laser ablation microprobe (UVLAMP) has been applied for the first time to investigate argon partition coefficients for olivines and clinopyroxenes grown from silicate melts at 1 bar argon pressure. These preliminary measurements yield crystal/melt partition coefficients ranging from 0.138 (±0.01) to 0.013 (±0.003) for olivine and 0.589 (±0.003) to 0.0016 (±0.0005) for clinopyroxene. The higher values may indicate sub-microscopic melt inclusions, or some other heterogeneous distributions of `non-equilibrium' argon in the crystals. The lower values are probably more representative of true partition coefficients and fall at least an order of magnitude below the previously reported experimental data. The possibility of anomalous, high argon contents for crystals in previous studies is discussed in terms of surface adsorption, `trapped' argon and early partial melting.

Description: Detailed investigations have been made of two amphibole samples where 40Ar/39Ar age spectra have been interpreted to show argon diffusive loss. Both samples display complex compositional zoning that reflects partial major and minor element chemical re-equilibration during later thermal events that is associated with the loss of radiogenic 40Ar. The apparent diffusive loss age spectra in these samples are an artefact of this chemical re-equilibration process. One sample additionally shows the effect of potassium gain and contamination with a potassium-rich phase (biotite). The resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental. This study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re-equilibration in amphiboles.

Description: 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.

Description: The photoactive yellow protein of Ectothiodospira halophila (PYP) was purified to homogeneity by an advanced method and applied as an affinity ligand for the isolation of an anti-PYP IgG fraction which was used for immunoscreening. The distribution of proteins immunologically related to PYP was investigated in protein fractions of 51 strains from 38 species of non-halophilic and halophilic phototrophic and chemotrophic eubacteria and archaeobacteria. Strong immunoreactive bands indicating the presence of authentic PYP on Western blots (apparent mass 17.8 kDa) was only found in the strains of E. halophila. Additionally, two soluble proteins of Chromatium salexigens and Rhodospirillum salexigens (apparent molecular masses 16.4 and 19 kDa, respectively) cross-reacted to approx. 6% and 4%. Analyses of cell fractions of E. halophila revealed that PYP is a cytoplasmic protein.

Description: The late Eocene through Oligocene changes in the paleoceanography of the southernmost Indian Ocean have been reconstructed by means of a coarse fraction analysis of closely spaced samples (20 cm = about 20 kyr) from ODP Site 744, Kerguelen Plateau. Surface water productivity, reconstructed from accumulation rates of opal skeletons and benthic foraminifers is low in the early late Eocene, increases at about 36 Ma and shows a sharp increase to maximum values in the earliest Oligocene. In the early late Oligocene it decreases gradually to a minimum and increases again to a maximum in the latest Oligocene. Beside this general trend productivity varies in short-term cycles of a duration of about 400 kyr (340 kyr in the latest Oligocene) with maxima in productivity in warmer Oligocene periods. These productivity variations are reflected by strong variations in carbonate dissolution. Changes in bottom water mass chemistry have been deduced from the degree of carbonate dissolution and it's relation to productivity proxies. Following Kennett and Stott (1990), it is suggested that a proto-antarctic bottom water (proto-AABW) and an overlying warm, saline deep water (WSDW) from low latitudes shifted vertically and latitudinally with time and exerted their influence on the sediments of Site 744. Proto-AABW is detected by means of strong carbonate dissolution when productivity is low. WSDW is detected by means of an excellent carbonate preservation despite high productivity. Terrigenous material occurs as very coarse ice-rafted detritus (IRD) in the late Eocene (167–168.5 mbsf) and after a main shift in oxygen isotopes in the early Oligocene. Very low amounts of 40–125 μm sized mica and very few quartz grains occur only in high productivity periods and at the transition from low to high productivity periods. These occurrences are attributed to wind/current supply during warmer Oligocene intervals.

Description: High resolution interdisciplinary analyses of the clay and coarse (〉40 μm) fractions of ODP Leg 113 Site 690 Eocene-Oligocene sediments on the flank of the Maud Rise, provide information on paleoproductivity, water masses, paleoclimate and erosion in the Antarctic range as well as on the cyclicity of these processes. Three time intervals are distinguished: 1. (1) The middle Eocene, characterized by (a) nearly pure smectites, (b) productivity varying between relatively high values in the 42–44 Ma interval to very low values after 42 Ma, and (c) cyclic variations which correspond to changes in clay mineral associations. A warm saline deep water mass is inferred to have protected carbonate shells against dissolution at Site 690. We interpret the abundant mica in the coarse fraction as distributed by intermediate currents. 2. (2) The latest middle Eocene-late Eocene, characterized by low productivity values increasing with time. Kaolinite and illite concentrations also increase. Since the middle/late Eocene boundary mixing in the water column, which starts during a cooling event, causes similar clay mineral assemblages at Site 690 and at Site 689 on top of Maud Rise. 3. (3) The Oligocene, separated from the Eocene by a hiatus, is characterized by high productivity, highly increased amounts of illite and other minerals originating from erosion and physical weathering of Antarctica, and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400–450 kyr cyclicity. Six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a “Proto-AABW” type.

Description: The concept of sequence-stratigraphy uses the stratal geometries at the margins of carbonate platforms to define depositional sequences and systems tracts. The aim of this study was to research if prograding, purely aggrading and retrograding phases of a Cretaceous carbonate platform showed differences in the composition and facies type of the slope sediments. The Vercors Plateau in SE France provides excellent outcrops to study this relationship. Continuous exposure of the platform-to-basin transition allowed direct examination of the margin geometries. Five successions were measured and sampled in great detail. Samples were thin-sectioned and point-counted, using point-count groups characterizing palaeoenvironments along the platform-to-basin transect. The composition logs as well as the numerical analysis of the point-count data, both show a clear relationship between grain composition and stratal geometry. The prograding and purely aggrading intervals are similar in composition, as they are both relatively coarse grained, and enriched in platform biota and limeclasts. Retreating units are relatively fine grained and rich in basinal grains (small benthic foraminifers, sponge spicules), non-carbonate grains and embedding material. These observations suggest that the retreating intervals represent incipient drownings of the platform. However, rather than distinctly separated groups the different phases of platform development form a continuous range of variation between high platform input and high basinal input. Compared to the prograding units the purely aggrading intervals are relatively rich in peloids, which may be suggestive of relatively low-energy conditions on the platform during aggradation. The compositional analysis also revealed significant variation in the frequency of ooids, but these variations showed no relationship with the progradation, aggradation or retreat of the platform.

Description: 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.

Description: A synchrotron microprobe has been used to characterize ion implantations of nickel and cobalt in silicon (100) or (111) wafers. The synchrotron radiation is collimated by means of a rigid cylindrical glass capillary of 110 mm length, 5 mm outer and 30 μm or 10 μm inner diameter. The beam is pointed at the wafer sample and the emitted radiation of X-rays is detected by an energy dispersive spectrometer. Line scans are recorded step by step over the implantation areas and across their borders. The sharpness of the borders is characterized at a lateral resolution of 13 μm and the edge lengths ranging from 0.6 to 8 mm are determined with an accuracy better than ± 20 μm. The signal intensity and implantation dose of cobalt ranging from 1 × 1015 to 1 × 1017 ions cm−2 show a linear relationship as is to be expected for the micrometre thin implanted layers.

Description: Dispersal characteristics of the T, We, Wn, Pu, Ps, Ye, Yn and Yb plinian fall deposits of Mount St. Helens have been measured at 80 sites downwind of the volcano in order to model eruption dynamics and atmospheric transport. Isopleth contours for the sizes of maximum pumice and lithic clasts are used to calculate peak eruption column heights and intensities (magma discharge) based on a theoretical model of tephra dispersal. New proximal thickness measurements are combined with an empirical distal extrapolation, based on studies of 53 plinian deposits, to calculate the magnitude (erupted mass) of each eruption. Layer Yn (3510 y r B.P.) represents the highest intensity and largest magnitude eruption at Mount St. Helens in post-glacial times. Modeling suggests column height grew to about 31 km before gradually declining at the end of the plinian phase (~ 26 hours). Several intraplinian surge deposits are present in the upper part of the fall layer close to the volcano and up to 15 km to the northeast of Mount St. Helens. Peak intensity of the plinian phase was 108 kg/s and the total erupted volume was 4 km3 (DRE of magma). Small plinian-style eruptions are represented by layers such as Ps and Pu of the Pine Creek eruptive period (3000-2500 yr B.P.) and have intensities of only ~ 106 kg/s. When compared with plinian eruptions from other volcanoes, the Holocene eruptions of Mount St. Helens span from the lower to the middle part of the known range in intensity and magnitude and are typical of events derived from intermediate-sized stratovolcanoes. There is also a general correlation between the intensity of plinian eruptions within eruptive cycles and the repose period prior to each cycle. This relationship may be related to a time-dependent process for the accumulation of differentiated and volatile-rich magma within the chamber beneath Mount St. Helens.

Description: 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.

Description: Granulometric and stable oxygen isotope analyses of four sediment cores from two high accumulation areas in the Skagerrak (NE North Sea) were carried out in order to reconstruct climate fluctuations and to evaluate climate impact during the upper Holocene. Extremely high sedimentation rates, especially in the eastern Skagerrak, are explained by increased current activity which is responsible for the transport and deposition of high quantities of suspension load during periods of stormy zonal atmospheric circulation patterns. These were most frequent during colder periods, while warmer phases are characterized by calmer meridional to zonal atmospheric circulation patterns. While the Subatlantic climate deterioration and the Subboreal climate optimum left only indistinct traces in the sediments, the Roman climate optimum and a colder period between ca. 400 and 700 AD are well documented. The following Medieval Warm period is characterized by a clear temperature increase of the waterbody in connection with less frequent advances of Atlantic water masses into the Skagerak deep and a decrease in bottom current strength. A mode of sedimentation prevails, similar to that of recent summer conditions, suggesting short and mild winters during that period. The onset of the Little Ice Age (around 1350 AD), however, shows an intensified bottom current circulation most probably due to amplifying westerly winds and a decrease in water temperatures in connection with more frequent advances of higher saline Atlantic waters. The Little Ice Age can be divided into 3 phases: a stormy “zonal” onset, a calm “meridional” maximum and a stormy “zonal” end. The stormy phases are characterized by a sedimentation mode similar to that of recent winter conditions while the Little Ice Age Maximum shows conditions comparable to exceptional cold modern winters. From 1900 AD, at the onset of the Modern Climate Optimum, the winter type sedimentation decreases and conditions change again to a level comparable to the Medieval Warm Period.

Description: Oxygen isotope ratios were obtained from authigenic clinoptilolites from Barbados Accretionary Complex, Yamato Basin, and Exmouth Plateau sediments (ODP Sites 672, 797, and 762) in order to investigate the isotopic fractionation between clinoptilolite and pore water at early diagenetic stages and low temperatures. Dehydrated clinoptilolites display isotopic ratios for the zeolite framework (δ18Of) that extend from +18.7‰ to +32.8‰ (vs. SMOW). In combination with associated pore water isotope data, the oxygen isotopic fractionation between clinoptilolite and pore fluids could be assessed in the temperature range from 25°C to 40°C. The resulting fractionation factors of 1.032 at 25°C and 1.027 at 40°C are in good agreement with the theoretically determined oxygen isotope fractionation between clinoptilolite and water. Calculations of isotopic temperatures illustrate that clinoptilolite formation occurred at relatively low temperatures of 17°C to 29°C in Barbados Ridge sediments and at 33°C to 62°C in the Yamato Basin. These data support a low-temperature origin of clinoptilolite and contradict the assumption that elevated temperatures are the main controlling factor for authigenic clinoptilolite formation. Increasing clinoptilolite δ18Of values with depth indicate that clinoptilolites which are now in the deeper parts of the zeolite-bearing intervals had either formed at lower temperatures (17–20°C) or under closed system conditions.

Description: Concentrations of hydrocarbon gases and stable carbon isotope ratios of methane from the water column of Shaban, Kebrit, Atlantis II and Discovery deeps, Red Sea, have been determined. Methane concentrations (yield C1) range from 〈 50 nL/L (Red Sea deep water) to ca. 22 × 10−3 L/L (Kebrit brine). Stable carbon isotopes of methane are between −30 and 43‰. Hydrocarbon gases in the brines are originally of thermogenetic origin (Kebrit: C1/C2∼ 57; δ13C1 ∼ −30‰). Methane concentrations in the transition zones between brines and Red Sea deep water decreased, especially in the Atlantis II/Discovery deeps, associated with a strong shift of δ13C1 to positive values. This shift is related to bacterial oxidation of methane in the transition zone between brine layers and overlying Red Sea deep water. Oxidized methane mixes with Red Sea deep water methane. A connection between the Atlantis II and the Discovery brine is postulated on the basis of the geochemical data.

Description: 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.

Description: The single scattering properties of nonspherical raindrops have been calculated by means of the geometric optics approximation to ascertain the usefulness of lidar remote sensing of rainrates. Based on the theoretical hydrodynamical studies of Chuang and Beard (J. Atmos. Sci., 1990, 47, 1374Ð1389), a Chebyshe¤-series of shape coe¦cients has been selected to account for the size dependent particle nonsphericity. The single scattering calculations for randomly oriented raindrops with particle radii ranging from 0.5 to 4.5mm exhibit a very pronounced dependence of the phase matrix on particle shape. However, most of these changes are not monotonic with increasing size, which complicates correlations between rainrates and the radiative properties of the raindrops. A comparison of ray tracing results by Chebyshe¤-type particles and axis-ratio equivalent spheroids shows signiÞcant di¤erences for particles with radii larger than 1 mm. Backscattering intensity as well as linear and circular depolarization ratios for horizontally oriented raindrops show a non-monotonic increase with particle size. The size distribution averaged backscattering properties are poorly correlated with rainrates. We conclude that lidar remote sensing of rainrates does not seem to be a promising attempt. However, this conclusion may be subject to changes if raindrop oscillations, which have not been considered in this study, a¤ect the size distribution averaged backscattering properties.

Description: 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.

Description: XCTD (eXpendable Conductivity Temperature Depth) probes, developed recently by SIPPICAN Inc., have been used simultaneously with a CTD sonde in order to test, in the field, their performance and accuracy (interpreted as ±2 standard deviations of the XCTD-CTD differences). We have taken advantage, during the THETIS-I experiment in March 1992, of both the homogeneous and the stratified areas encountered in winter in the northern part of the western Mediterranean Sea to differentiate the errors due to the experimental conditions from those effectively due to the sensors. Although some intrinsic problems are evident, so that only seven out of the nine probes considered for comparison are usable, the accuracy specified by the manufacturer for the temperature (AT = ± 0.03°C) is reached after standard processing, while the accuracies in conductivity, salinity and potential density are AC ≈ ± 0.06 mS/cm (the specified value is AC = ± 0.03 mS/cm), AS ≈ ± 0.04 and Aσθ ≈ ±3 kg/m3. However, when the experimental errors (in situ natural variability, relatively rough estimation of the XCTD depth) are considered, it appears that the effective accuracies of the XCTD sensors are better than ± 0.02°C and ± 0.04 mS/cm, that is to say better than and close to the specified values of ± 0.03°C and ± 0.03 mS/cm. Occasional offsets in conductivity can further be well corrected for by using a temperature-salinity relation in some limited depth range and area where this relation is known to hold well; the conductivity-sensor accuracy then significantly improves to AC≈ ± 0.02 mS/cm resulting, for our study area, in corresponding salinity and potential density accuracies of AS≈ ± 0.03 and Aσθ ≈ ± 0.02 kg/m3. Thus, such instruments promise to be useful tools for many experimental studies. Complementary comparisons, performed with new versions of the XCTD probes under less convenient experimental conditions, are also presented

Description: Concentrations of 23 individual chlorobiphenyls (CBs) and 6 polyaromatic hydrocarbons (PAHs) were determined in different water masses of the North Atlantic Ocean around Iceland. The study was carried out in the framework of the second Intergovernmental Oceanographic Commission (IOC) baseline studies of contaminants in the North Atlantic Ocean, involving trace organics and trace elements. Concentrations of individual CBs were extremely low. In solution, they varied between 〈2 and 126 fg dm−3 and in suspension between 〈2 and 1400 fg dm−3. The values for their sum (∑CB) were between 10 and 1048 in solution, and 286–11 241 fg dm−3 in suspension. ∑PAHs were present in the 〈5–65 pg dm−3 range, p,p′-DDE and hexachlorobenzene were 〈2 fg dm−3. The concentrations of CBs and PAHs decreased from the surface towards the bottom at each station. The lowest concentrations were found in Norwegian Sea Deep Water (∑CB 10 fg dm−3), concurrent with the lowest halocarbon concentrations found during the cruise. Values in near-surface waters were considerably lower than those determined at mid-latitudes of the North Atlantic. These findings reflect the mixing of water bodies with higher CB concentrations from the central North Atlantic with less contaminated waters from the Arctic Ocean. Concentrations in suspension exceeded those in solution in most samples, as a result of the relatively high suspended matter concentrations in the waters around Iceland. Particulate CB and PAH concentrations were positively correlated with particulate organic carbon concentrations. This suggests that suspended organic material is a carrier for these relatively apolar organic compounds in the water column. The data do not support the co-distillation concept suggested in the literature.

Description: 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.

Description: In 1995, we participated in a number of WOCE Hydrographic Program cruises in the Indian Ocean as part of the Joint Global Ocean Flux Study (JGOFS) CO2 Survey sponsored by the Department of Energy (DOE). Two titration systems were used throughout this study to determine the pH, total alkalinity (TA) and total inorganic carbon dioxide (TCO2) of the samples collected during these cruises. The performance of these systems was monitored by making closed cell titration measurements on Certified Reference Materials (CRMs). A total of 962 titrations were made on six batches of CRMs during the cruises. The reproducibility calculated from these titrations was ±0.007 in pH, ±4.2 μmol kg−1 in TA, and ±4.1 μmol kg−1 in TCO2. The at-sea measurements on the CRMs were in reasonable agreement with laboratory measurements made on the same batches. These results demonstrate that the CRMs can be used as a reference standard for TA and to monitor the performance of titration systems at sea. Measurements made on the various legs of the cruise agreed to within 6 μmol kg−1 at the 15 crossover points. The overall mean and standard deviation of the differences at all the crossovers are 2.1±2.1 μmol kg−1. These crossover results are quite consistent with the overall reproducibility of the CRM analyses for TA (±4 μmol kg−1) over the duration of the entire survey. The TA results for the Indian Ocean cruises provide a reliable data set that when combined with TCO2 data can completely characterize the carbonate system.

Description: 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.

Description: The possibilities of defining and computing an approximately neutral density variable are reexamined in this paper. There are three desirable properties that a neutral density variable should possess. Firstly, the isosurfaces of this variable should coincide with (approximately) neutral surfaces. This would facilitate the analysis of hydrographic data on the most appropriate mixing and spreading surfaces. Secondly, the horizontal gradients of the neutral density should agree with the gradients of the in situ density, and thirdly the vertical gradient of the neutral density variable should be proportional to the static stability of the water column. A density variable that approximates the latter two properties can be used in ocean circulation models based on layer coordinates, and would reduce substantial errors in present isopycnal models due to the use of a potential density variable. No variable can possess all the three properties simultaneously. The variable γn introduced by Jackett and McDougall (1997, J. Phys. Oceanogr. 27, 237–263) satisfies the first of the properties exactly but is not designed for the use in models. Based on climatological data in the North Atlantic, an alternative neutral density variable ν̃(S, Θ) is defined, which is shown to approximate the two gradient criteria much better than any potential density. We suggest that this neutral density variable may be useful in isopycnal ocean models as an alternative to potential density, since it could significantly reduce errors in thermal wind relation and vertical stability

Description: New sea-level and δ18O curves for the past 34,000 yr, based on uranium–thorium chronology, are proposed for the southwestern part of the Indian Ocean. The archives include cores drilled from onshore coral reefs and submersed samples from foreslope corals of Mayotte in the Comoro Islands. The Mayotte sea-level curve shows a lowstand of 145 ± 5 m below the present level during the last glacial maximum dated at 18,400 yr. This lowstand is supported by the maximum18O enrichment in the coral colonies. The residual signal (Δδ18O), controlled by sea-surface temperature changes, indicates that surface waters 18,400 yr ago were approximately 5°C cooler than present. The deglacial sea-level rise is clearly recorded, with a mean rate of about 1.7 cm yr−1between 18,400 and 10,000 yr ago. The deglaciation phase is characterized by a strong18O depletion marked by two pulses related to meltwater discharges into the North Atlantic Ocean but also characterized by responses specific to the tropical Indian Ocean.

Description: 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%)

Description: A system for in-situ filtration and extraction of organics in natural waters has been developed and tested down to 4000 m in the Atlantic Ocean. Up to 2000 dm3 water can be filtered and extracted at low suspended matter concentrations. The sampling equipment has new features for the analysis of trace organic compounds: contamination is extremely low, this can be checked and cured, if necessary, and water flow can be selected and maintained at a constant rate. Various resins can be applied, with different optimum flow rates for the efficient extraction of the compounds of interest. The properties of the resin (here XAD-2) do not change with depth. The operation of the unit is controlled by menu-driven software. All relevant data are stored for later evaluation. Tests in the deep Atlantic resulted in total procedural blanks, including sampling, as low as 0/003 pg dm−3 for individual chlorobiphenyls (CBs), HCB and DDE and 0.5 pg dm−3 for individual PAHs. Actual dissolved concentrations were in the range 0.005–0.1 pg dm−3 for CBs, HCB and DDE and 0.5–140 pg dm−3 for PAHs.

Description: 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.

Description: Two single-operator multiparameter metabolic analyzers (SOMMA)-coulometry systems (I and II) for total carbon dioxide (TCO2) were placed on board the R/V Knorr for the US component of the Indian Ocean CO2 Survey in conjunction with the World Ocean Circulation Experiment-WOCE Hydrographic Program (WHP). The systems were used by six different measurement groups on 10 WHP Cruises beginning in December 1994 and ending in January 1996. A total of 18,828 individual samples were analyzed for TCO2 during the survey. This paper assesses the analytical quality of these data and the effect of several key factors on instrument performance. Data quality is assessed from the accuracy and precision of certified reference material (CRM) analyses from three different CRM batches. The precision of the method was 1.2 μmol/kg. The mean and standard deviation of the differences between the known TCO2 for the CRM (certified value) and the CRM TCO2 determined by SOMMA-coulometry were −0.91±0.58 (n=470) and −1.01±0.44 (n=513) μmol/kg for systems I and II, respectively, representing an accuracy of 0.05% for both systems. Measurements of TCO2 made on 12 crossover stations during the survey agreed to within 3 μmol/kg with an overall mean and standard deviation of the differences of −0.78±1.74 μmol/kg (n=600). The crossover results are therefore consistent with the precision of the CRM analyses. After 14 months of nearly continuous use, the accurate and the virtually identical performance statistics for the two systems indicate that the cooperative survey effort was extraordinarily successful and will yield a high quality data set capable of fulfilling the objectives of the survey.

Description: 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.

Description: To investigate patch selectivity in aspidochirotide holothurians, individuals of five species (Holothuria (Halodeima) atra Jäger, H. (H.) edulis Lesson, H. (Microthele) nobilis Selenka, Stichopus chloronotus Brandt and S. variegatus Semper) were subjected to multiple choice experiments. As a food source, sediments were pre-cultivated in petri dishes under different light and nutrient regimes. This resulted in four sediment treatments with different levels of microalgal biomass (measured as chlorophyll a and phaeophytin concentrations). Only two sediment treatments were used for experiments with H. nobilis and S. variegatus. The sediments were offered simultaneously to individual holothurians (six per experiment), and the weights of the sediment in each petri dish at the start and after 48 h were used to calculate a selection index together with confidence intervals for each food type. In experiments with H. atra and H. edulis, the animals exhibited no preference for any food type. In contrast, S. chloronotus significantly selected sediments with the highest contents of microalgae and avoided the sediment with the lowest pigment concentrations. These results were supported by field collections of sediments found directly underneath holothurians. Sediment underneath H. edulis did not differ from the average sediment of the habitat, while H. atra was found on sediments only slightly higher in chlorophyll a. Chlorophyll a concentrations underneath S. chloronotus were distinctly higher than in the adjacent sediment and that underneath H. atra. H. nobilis showed only a weak preference for sediments with higher pigment concentrations in aquarium experiments, and no patch selectivity in this species was found in the field. Stichopus variegatus exhibited a very distinct patch selectivity towards sediments with more nutritional value in both aquaria experiments and field measurements. Thus members of the genus Holothuria had no, or only a weak, tendency to select their food source, whereas both Stichopus species appeared to carefully select the sediment patch to feed on.

Description: Metabolism of chlorobiphenyls (CBs) was studied in harbour porpoise by comparing patterns of CB-X/CB-153 ratios in blood, brain, liver and blubber with the patterns in herring, the main food source. The CBs were classified in five groups, based on the presence/absence of vicinal H-atoms (vic. Hs) in meta,para (m,p) and/or ortho,meta (o,m) positions and the number of ortho-Cl-atoms (ortho-Cls). Plots of CB-X/CB-153 ratios in porpoise tissue vs the ratios in herring appeared to be linear for each CB group in all tissues. Slopes of these plots (metabolic slopes) were used as quantitative indicators of metabolic activity. In this way, activity of PB-type isozymes of the P450 monooxygenase system was apparent: in contrast to existing literature data, harbour porpoise appears to be able to metabolize congeners with m,p vic. Hs, even in the presence of more than 2 ortho-Cls. The presence of 3-MC-type (MC-type) isozymes was also detected. The metabolic slopes were also used as basis for risk assessment. Due to their metabolism the most toxic non-ortho CBs were not present in the tissues at detectable levels. We suggest a risk assessment approach which takes this into account. It is considered to be an alternative and more reliable basis for risk assessment than the use of toxic equivalent factors. The results support the model of equilibrium distribution of CBs in harbour porpoise and the role of blood as central transport medium. The model has been developed for persistent compounds; it appears to hold for metabolizable CB congeners as well.

Description: 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.

Description: The form of the Deccan-Maldives-Mascarene-Réunion hotspot trace suggests that it has, at least in part, been strongly controlled by crustal structures, especially fracture zones. This makes it difficult to assess the present-day or past location of the hotspot, and thus complicates the interpretation of African plate motion reconstruction. We present here results of a cruise to the Réunion area of which the aims were: (a) to determine the extent of present-day volcanism associated with the Réunion hotspot in the region; and (b) to examine the rôle of pre-existing oceanic crustal structures in controlling the location of present-day volcanism. Additionally, we examined the morphology and geology of the important extinct spreading centre southwest of Réunion abandoned when spreading jumped to separate Seychelles from India during the Deccan flood basalt episode some 60–65 Ma ago. The extensive bathymetrie, seismic and geological investigation shows that significant present-day hotspot volcanism is confined to the Piton de la Fournaise edifice on Réunion Island itself. Apparently, the location of recent Réunion volcanism has not been controlled by a crustal fracture and the major fracture zones on both sides of the island are not acting as magma conduits. For plate motion reconstruction and plume flux calculation purposes, Piton de la Fournaise must be taken as the present location of the Réunion hotspot. Accretion at the extinct spreading centre progressively ceased at the time of anomaly A27 (63 Ma), and was associated with marked propagation of the rift tips.

Description: In an extended deep-sea study the response of the benthic community to seasonally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L2 at 47°N–20°W, water depth 〉4500 m) on four legs of METEOR expedition 21 between March and August 1992. The vertical flux at 3500 m depth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phospholipids, measures of benthic biomass, and of activity of hydrolytic enzymes were observed. The flux patterns in moored sediment traps of total chlorophyll, POC and total flux showed an early sedimentation peak in March/April 1992, followed by low fluxes in May and intermediate ones from June to August. Thus 1992 differed from other years, in which one large flux peak after the spring phytoplankton bloom was observed. Unusually high concentrations of chloroplastic pigments were consistently observed in March 1992, reflecting the early sedimentation input. At the same time biomass of small benthic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following months in 1992. In May and August 1992 pigment concentrations and biomass and activity parameters in the sediment were lower than during previously observed depositions of phytodetrital matter in summer. The data imply that the deep ocean benthic community reacts to small sedimentation events with transient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannual variability in surface water production is “mirrored” by deep-sea benthic processes.

Description: A geochemical rock- and soil-sampling program was carried out in the vicinity of eight concealed “Cyprus type” deposits, occurring in marginal mafic to intermediate metapillow lavas of the Troodos Ophiolite Complex. The mineralization of massive and stockwork sulfide ore is characterized by the predominance of pyrite, intergrown with less chalcopyrite and minor amounts of sphalerite. Background values of Hg are in the range of 8–12 ppb for soils and 3–6 ppb for surface rocks. Anomaly/background ratios of 10:1 (soils) and 5:1 (rocks) have been found only, where Hg migrated along channels formed by faults cutting shallow-seated mineralization. Here, Hg sometimes shows significant correlations with Cu, Zn, Ba and exceptionally with Co. However in one case an Hg anomaly in soils and surface rocks was detected directly over a deposit. The use of Hg as indicator element for these types of deposits is therefore limited. Buried mineralization may be delineated more distinctly by Cu, Zn and Ba.

Description: Both living (stained) and dead (unstained) foraminiferal assemblages from surface sediments (0–2 cm) in the northwestern part of the Skagerrak have been studied in order to (1) define and characterize the distribution of various modern benthic environments and (2) by comparing these findings with surface samples collected 40–60 years ago, to document possible faunal changes that might have occurred. The investigated area is physiographically divided into the Norwegian slope, the Skagerrak Basin, and the Danish slope. The latter is under the influence of the Jutland Current, while the basin and the investigated parts of the Norwegian slope are bathed in Atlantic water. All areas have bottom waters with a high oxygen concentration. Three living (stained) and three dead (unstained) assemblages occupy the three physiographic areas. Only one assemblage (on the Norwegian slope) is common to both the living and dead assemblages but the boundaries between them lie at comparable depths. The higher standing crops are found on the fertile Danish slope while the lower ones are in the deep basin where the diversity is at a maximum. In the dead assemblages, the relative abundance of agglutinated tests increases with depth. Comparison with data collected 40 to 60 years ago shows increases in absolute numbers of tests, especially in the deep basin. There are changes in assemblage compositions in all areas. The dominant species found in 1937 are different from those of 1992/1993. There is a major change in the basin where one agglutinated species has changed its depth distribution downslope and two present day abundant species are new arrivals. These faunal events are probably linked to environmental changes.

Description: Investigations of living (stained) benthic foraminifera in the surface (0–1 cm) sediments along a depth transect in Drammensfjord, southern Norway, have been carried out on samples collected in 1984 and during all four seasons in 1988. The transect runs through strongly variable environments from a well oxygenated, brackish surface layer to anoxic waters of slightly less than normal marine salinity. The objectives were to study foraminiferal recolonization patterns after a prolonged period (〉 5 years) of nearly permanent anoxic bottom water conditions in the lower parts of the transect, the seasonal stability of the assemblages after recolonization, and interspecific tolerances to various environmental parameters (i.e., temperature, salinity, dissolved oxygen concentration, water depth). When the redox-boundary was at its shallowest position in the water column (30–35 m water depth; salinity 29–30 ‰), Ammodiscus? gullmarensis was dominant adjacent to the anoxic areas. This represents the first record of agglutinated dominated assemblages bordering anoxic environments. It took more than one year after reaeration before the areas, where anoxic conditions had prevailed for more than five years, became suitable for colonization. By 1988, the foraminiferal standing crop had more than doubled in areas influenced by the transitional water masses and living (stained) individuals were present down to the redox-boundary. Additionally, four species, which were not found along the transect in 1984, had been introduced. These immigrants had probably been transported into the area in suspension from the south. Stainforthia fusiformis was the first and most successful species to recolonize the formerly anoxic areas and it showed exceptionally high densities in samples collected a few meters above the redox-boundary. After recolonization, all species showed a distinct depth succession which, for most of them, prevailed throughout the year. Possible lack of seasonal population fluctuations in several species is thought to be due to a permanently plentiful food supply. The nine abundant species have been ranked in accordance with their interspecific tolerance to increasing euryhaline and eurythermal environmental conditions.

Description: This is the first detailed investigation of the distribution and ecology of living (stained) shallow water (0–6 m) foraminifera along the Skagerrak–Kattegat coast, eastern North Sea. A total of 25 species (13 agglutinated; 12 calcareous) are common in the 169 sediment surface samples which were collected from 27 geographic areas. The sediment grain size and total organic carbon (TOC) content are strongly variable and the salinity and temperature ranges were 10–31‰ and 9–30°C, respectively, at the time of sampling (July to October) but temperatures down to freezing occur during the winter. The species are divided into six environmental categories of which the first five comprise euryhaline and the sixth essentially stenohaline taxa: (1) species associated only with marsh plants, (2) species basically, but not entirely, associated with marsh plants, (3) species basically, but not entirely, restricted to non-marsh areas, (4) species solely recorded in non-marsh intertidal to subtidal environments, (5) species restricted to subtidal areas, (6) species basically living in the most open marine areas. In this region, marshes have a patchy distribution and they are small and compressed due to low tidal ranges (〈40 cm). Balticammina pseudomacrescens (not reported here before) lives in the most elevated, landward, terrestrial parts of marshes and thus defines the uppermost limit of the influence of marine water. However, the marshes are generally dominated by Jadammina macrescens and Miliammina fusca at the landward and seaward sides, respectively. Jadammina macrescens is observed living epiphytically on decaying Carex leaf debris. The most widely distributed euryhaline species are Elphidium williamsoni, Miliammina fusca, Ammonia beccarii, and Haynesina germanica. The former two are common only in sediments with a mud content less than about 60%, whereas the latter two are common even in sediments with 〉80% mud. Ammoscalaria runiana is common only in coarse-grained sediments (〈20% mud) with low TOC (≤0.7%). There are no marked biogeographic boundaries within the Skagerrak–Kattegat area but 10 of the 25 commonly occurring species have not been reported from the adjacent Baltic Sea, probably partly due to the brackish character of the water there. The southern limits of distribution of the northern species, Elphidium albiumbilicatum, Ammotium cassis, and Ophthalmina kilianensis, are in the Kattegat–Baltic Sea.

Description: Food production is affected by climate and by climate change. The indices for climate change may be recognized in long-term systematic observations of oceanic water columns at selected referential sites. The Mediterranean Sea, as part of the global oceanic circulation system, may be sensitive to climatic variation and may have an influence upon climate. The establishment of international referencestations for the Mediterranean area is suggested.

Description: The role of TEP (Transparent Exopolymer Particles) in the flocculation of a diatom bloom was studied under controlled conditions in a mesocosm. The concentration of TEP increased exponentially during growth, flocculation and senescence of the bloom. Aggregation began dominating the particle dynamics of TEP during the early growth phase of the bloom, several days prior to the appearance of large flocs and nutrient depletion. TEP aggregated with themselves and with phytoplankton due to the high stickiness of TEP, but phytoplankton was not observed to aggregrate with itself. The production of TEP, estimated from changes in concentration, did not increase after nutrients were depleted. The concentration of TEP was a linear function of chl a and particulate organic carbon (POC), indicating that production of TEP was linked to growth rather than standing stocks of phytoplankton. The ratio between TEP and phytoplankton appeared to be one of the factors determining the onset of the flocculation of the bloom. The concentration of TEP may have been decreased by bacterial degradation. Bacterial degradation of TEP may explain the low TEP to chl a values, the decrease in stickiness of particles as the bloom progressed, and the retarded onset of flocculation.

Description: Sequences of the 16S rRNA gene were determined from all type strains of the recognized Ectothiorhodospira species and from a number of additional strains. For the first time, these data resolve the phylogenetic relationships of the Ectothiorhodospiraceae in detail, confirm the established species, and improve the classification of strains of uncertain affiliation. Two major groups that are recognized as separate genera were clearly established. The extremely halophilic species were removed from the genus Ectothiorhodospira and reassigned to the new genus Halorhodospira gen. nov., to recognize that the most halophilic eubacteria are species of this genus. These species are Halorhodospira halophila comb. nov., Halorhodospira halochloris comb. nov., and Halorhodospira abdelmalekii comb. nov. Among the slightly halophilic Ectothiorhodospira species, the classification of strains belonging to Ectothiorhodospira mobilis and Ectothiorhodospira shaposhnikovii was improved. Several strains that were tentatively identified as Ectothiorhodospira mobilis form a separate cluster on the basis of their 16S rDNA sequences and are recognized as two new species: Ectothiorhodospira haloalkaliphila sp. nov., which includes the most alkaliphilic strains originating from strongly alkaline soda lakes, and Ectothiorhodospira marina, describing isolates from the marine environment.

Description: Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32°27.631′N, 127°49.489′W; 32°27.581′N, 127°47.839′W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects.

Description: A high resolution Pb isotope time-series for the last 26 Ma, dated by 10Be/9Be chronology, is reported for a north Indian Ocean ferromanganese crust. This record is compared with available Pb isotope time-series of six other crusts from the Atlantic, Indian and Pacific Oceans, each of which is based on 10Be/9Be chronology. The seven Pb isotope records reveal some remarkable features. In contrast to the Nd isotope time-series of these crusts which show a long-term (∼60 Ma) provinciality between the three main ocean basins, the Pb isotopes only show comparable provinciality over the last ∼5 Ma. Prior to about 15 Ma ago no distinct Indian Ocean Pb isotope signal existed. Within this established framework of Pb isotope distribution in the oceans the 208Pb/206Pb data for the north Indian Ocean crust reported here are anomalous. The 208Pb/206Pb ratio is particularly high and exceeds a value of 2.08 during the time interval from 20 to 8 Ma ago. Consideration of potential sources of Pb in the Indian Ocean which might provide such high 208Pb/206Pb ratios suggests that this crust most probably has recorded a time-varying erosional input of Pb from the Himalayas. The timing of the isotopic shift is in good agreement with maximum Himalayan exhumation rates deduced from crystallisation and cooling ages of synorogenic granites (20–14 Ma) and the sedimentation history of the Bengal Fan.

Description: The Ocean Margins Program, an interdisciplinary study focussed at Cape Hatteras, is evaluating whether this region is a net source or sink for carbon, while concurrently developing a mechanistic understanding of the production, cycling and fate of organic carbon. Preliminary to a large multi-ship field program in 1996–1997, the first of several short cruises surveyed Cape Hatteras in May 1993. High concentrations of chla occurred across the shelf. Stations and depths at which chla was highest also showed elevated concentrations of large phytoplankton, predominantly chained diatoms, but also single-celled dinoflagellates and obligately photosynthetic ciliates. These populations occurred in deeper waters, however, and their abundance was poorly correlated with proxies of community photosynthesis. Instead, small phototrophic nanoplankton, abundant in surface waters, were positively correlated with primary production. Carbon budgets indicated that inner shelf waters containedca 50% more living POC than outer shelf waters. The relative importance of large phytoplankton and grazers decreased with distance offshore, and they were replaced by photosynthetic nanoplankton and microzooplankton. Even greater changes in living POC occurred in the alongshore direction due to the dramatic reductions in diatoms in southern waters. Estimated herbivory wasca 2–4 gC m−2 d−1. The ratio of heterotrophic : autotrophic POC increased from 38% in northern waters to 137% in southern waters, suggesting that phytoplankton was being converted into consumer carbon as shelf waters advected south. The dominant consumers at most stations were single-celled protozoan zooplankton and small copepods, whose fecal products remain in suspension in energetic shelf environments, suggesting that much of the non-diatomaceous POC was exported as shelf waters exited at Cape Hatteras.

Description: A mega-submarine slide was evidenced along the Peruvian margin during a Seabeam survey of the R/V Charcot (Bourgois et al., 1986). The debris-slide was initially interpreted as the result of the slope failure occurring along a seaward curved scarp, and extending from east to west, along the line of maximum slope. Complementary bathymetrie data obtained from the R/V Sonne survey conducted to the north and to the south of the previous surveyed area has resulted in the identification of large-scale polyphase submarine slides involving a total surface of about 1000 km2, between latitudes 5 °15′S and 6 °05′S. Using Seabeam and Hydrosweep multibeam echosounder data in combination with deep-sea submersible observations, three distinct slope-failure types related to three main stages have been revealed. The three sliding phases occurred roughly along the same trend, orientated N230 °, and are therefore mainly controlled by the N80 ° orientation of the subducting Nazca plate. (1) The first phase of slope failure is documented by a debris-avalanche deposit, which extends from the lower slope down to 5 km within the trench floor. The deposit originates from the northern wall of a wide valley located along the upper slope. (2) The second phase of slope failure is characterized by a debris-avalanche, with a crescent-shaped scar, located along the middle slope and a hummocky deposit covering the lower slope and extending up to 10 km across the trench. The volume of rock involved in this event is estimated to some 250 km3. The slope failure is assumed to be related to an oversteepening of the middle slope induced by a rollover deformation. (3) The third phase of slope failure corresponds to a translational sliding block and a toppling block with volumes of 6 km3 and 13 km3, respectively. The seismic energy produced during the seismic cycle has greatly increased facturation and fluids buildup along the area previously weakened by a rollover fold. A restricted N-S folding is observed in the vicinity of the trench, to the north of the two debris-avalanche deposits. It may have formed in relation to the local compression limited to the subduction of the Nazca plate. Sliding and folding thus document the paradox between the compressive regime in the lower plate and the extensional regime in the upper part of the upper plate.

Description: The percentage of the structural Fe(II) in clay minerals that is readily oxidized to Fe(III) upon contact with atmospheric oxygen was determined across the downcore tan–green color change in Peru Basin sediments. This latent fraction of reactive Fe(II) was only found in the green strata, where it proved to be large enough to constitute a deep reaction layer with respect to the pore water O2 and NO3−. Large variations were detected in the proportion of the reactive Fe(II) concentration to the organic matter content along core profiles. Hence, the commonly observed tan–green color change in marine sediments marks the top of a reactive Fe(II) layer, which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments. This is also demonstrated by numerical model simulations. The findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached, provided that the sediments contain a significant amount of structural iron in clay minerals.

Description: Pelitic schists from the lower garnet to lower staurolite zones from the Rangeley, Perry Mountain, and Smalls Falls formations of western Maine were analyzed for major elements, trace elements, and neodymium isotopes. These formations were derived from highlands created during the Taconian orogeny, deposited into a trough, and metamorphosed during subsequent orogenic events. Most major and trace element abundances relative to Al2O3 were statistically identical between zones of the same formation, as well as between formations. Although the average major element composition of these formations are the same, there are systematic variations in some elements. Notably, plots of SiO2 vs. Al2O3 and K2O vs. Al2O3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system. Different amounts of these minerals should not influence the shape of the REE patterns of the metapelites, but higher amounts of quartz and feldspar may dilute the REEs and most elemental abundances of the clay minerals and lead to lower elemental abundances. The major difference between the samples within the Perry Mountain Formation are different LREE and MREE abundances relative to Al2O3 which are not correlated to differences in major element or other trace element abundances relative to Al2O3. The samples in the Perry Mountain with higher LREE and MREE abundances have, for example, 42.3 ± 8.3 ppm, and those with low abundances have 5.6 ± 3.6 ppm. The samples with the high REE abundances of the Perry Mountain Formation are similar in abundances and REE patterns to those of the Rangeley and Smalls Falls formations typical of mudstones derived from granitoids. Another difference between the low and high REE abundance samples are the calculated Tdm model ages. The high REE abundance samples of the Perry Mountain Formation show Tdm similar to the samples of the Rangeley Formation, with ages of about 1.7–1.8 Ga. The Perry Mountain samples with low REE abundances, however, give unrealistically old Tdms between 2.5 and 5.3 Ga. These unrealistically old Tdms are due to the relatively high Sm/Nd ratios (compared to crustal values) which are characteristic of samples of the Perry Mountain Formation with lower REE abundances. We therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system. The timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event. The complexities of the data suggest more than one resetting event. The most likely event that could have produced much of the movement of the LREEs and MREEs could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis, but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data.

Description: A coulometrically-based SOMMA system for the determination of total dissolved carbon dioxide (TCO2) in a continuous mode was designed and tested at sea. The new continuous technique approached the same high accuracy and reliability associated with prior discrete TCO2 measurements. During three cruises encompassing more than 19 weeks and 6000 continuous TCO2 measurements none of the three different systems tested exhibited any hardware-related failures. We found that coulometer cell lifetimes can greatly exceed prior expectations with many of the titration cells in the continuous mode remaining accurate for up to 72 h at carbon ages exceeding 50 mg C. We suggest a practical definition based on the CRM analyses for changing coulometer cells in the continuous mode. Systematic deviations of the SOMMA pipette volume from a theoretical temperature dependence were identified both from field data comparisons and pipette calibrations. Hence pipettes should be kept at constant temperature or they must be gravimetrically calibrated over the expected temperature range. Comparison of the continuous TCO2 data together with simultaneously measured additional CO2 system parameters showed that the refitted “Mehrbach” dissociation constants for carbonic acid best-represent fCO2 when calculated from TCO2 and alkalinity over a wide range of sea-surface temperatures and salinities. Some remaining systematic differences of calculated–measured fCO2 of up to 9 μatm likely reflect uncertainty in the temperature-dependence of the “Mehrbach” constants as well as possible uncertainty in the alkalinity–salinity relationship used to estimate alkalinity in the consistency checks.

Description: An unrealistically high-salinity maximum is found to develop in a high-resolution model of the north and equatorial Atlantic below the shallow halocline in the Gulf of Guinea. The spurious water mass with salinities too high by as much as 1 psu is formed when the vertical advection is treated by the standard central-differencing advection scheme. The problem is considerably reduced either by increasing the vertical resolution of the numerical grid, or by switching to a higher-order upwind-weighted scheme for vertical advection. This note stresses the need for a careful consideration of vertical discretization even in typical high-resolution ocean general circulation models (OGCMs). Particular attention is needed for studying heat and salt budgets or transports of biogeochemical tracers.

Description: A PYE 2-(1-pyrenyl)ethyldimethylsilylated silica gel] column HPLC in combination with MDGC-ECD has been developed for a sensitive and selective determination of toxic mono- and non-ortho PCBs in environmental samples. This technique was applied to environmental samples such as coastal water, suspended particulate material (SPM), coastal sediment, mussels, fish, bird and marine mammal. Determination of PCB 156 along with non-ortho congeners acted as matrix-integrated quality control parameter. This hyphenated technique offers one of the most sensitive way of determining non-ortho PCBs but also reveals the immense complexity of the coelution problem which unnoticed results in over estimation of toxic PCBs in the environmental samples.

Description: Data on the carbonate system of the Northwestern Indian Ocean obtained on a cruise of F.S. Meteor during SW monsoon in July/August 1995 were compared with those of George et al. [George, M.D., Kumar, M.D., Naqvi, S.W.A., Banerjee, S., Narvekar, P.V., de Sousa, S.N., Jayakumar, D.A., 1994. A study of the carbon dioxide system in the northern Indian Ocean during premonsoon. Mar. Chem. 47, 243–254] collected during intermonsoon. In general, deep water values agreed well between the two expeditions. Surface waters, however, showed a substantial increase in dissolved inorganic carbon (CT) in the coastal regions due to strong upwelling in the SW monsoon. This was also accompanied by very high CO2 partial pressures in surface waters. The north–south gradients in vertical profiles of the measured parameters in the Arabian Sea are discussed by comparing profiles from the oligotrophic equatorial region with those from the highly productive central Arabian Sea. The effect of denitrification on regenerated CT and AT is minor, with contributions of 〈9 and 〈8 μmol kg−1, respectively, to the total amount regenerated also utilizing oxygen. The dissolution of biogenic carbonates is discussed; different approaches to define the depth, where the dissolution starts (lysocline(s), carbonate critical depth (CCrD)), are compared together with the calculation of saturation depth from carbonate concentrations. It is shown, that small differences in measured CT and AT (found between our data and those measured during GEOSECS) and different calculation approaches to the CO2 system (different dissociation constants for species involved and taking into account phosphate and silicate concentrations) can produce pronounced differences in the calculated saturation depths. However, CT and AT data suggest substantial dissolution of biogenic carbonate in the water column even above the calcite lysocline, irrespective of the procedures followed to calculate this horizon.

Description: High biogenic silica (BSi) concentrations (maximum: 11.7μmoll−1) were recorded during late November at the southern border of the Polar Frontal region (PFr). Position of the BSi maximum at depth suggested the occurrence of a sinking diatom population. By contrast, siliceous biomass was low (BSi 〈0.6 μmol l−1) in the Marginal Ice Zone (MIZ) despite a sea-ice retreat of 200 km during the study period. Diatoms released from the receding ice were not actively growing. The Permanently Open Ocean Zone also showed very low BSi biomass (〈0.5μmol l−1) and appeared as an area where phytoplankton are not dominated by siliceous organisms, especially in its middle part where BSi/POC (particulate organic carbon) molar ratios ranged between 0.04 and 0.06 at 53°S, from surface to 200 m depth. At the southern border of the PFZ, the bloom coincided with an area of high lithogenic silica concentrations probably of aeolian origin. In addition, BSi/POC molar ratios measured in the PFZ were the highest ever recorded in the surface waters of the Southern Ocean (maximum: 1.75). This could be due to the presence of heavily silicified diatoms such as Fragilariopsis kerguelensis or also could reflect the more rapid recycling of POC as compared to BSi. Within the bloom area BSi concentrations were positively correlated to pyrophaeophytin pigments, possibly indicating the occurrence of a senescent diatom population. High concentrations of BSi (〉 1.5 μmol Si 1−1) extended to 200 m between 49°S and 51°S. Numerous empty frustules also were observed, suggesting significant sedimentation of siliceous particles between 49°S and 51°S. Estimates of the BSi production of the Polar Frontal region are derived from 14C primary production and appropriate BSi/POC ratios, and implications for the total annual production of BSi for the Southern Ocean are discussed.

Description: The fatty acid composition of 27 strains from 7 described Ectothiorhodospira species, including all type strains, were analyzed and compared using the “Microbial Identification System”. According to their ability to grow in media with 15% total salts and more or to require much lower salt concentrations the comparison of the strains was made in two different groups. The strains grown in the established standard medium for Ectothiorhodospira species at 15% and 25% (w/v) salinity formed four major clusters. Two of these enclosed strains of E. halophila, the others E. abdelmalekii (one strain) and E. halochloris (3 strains), respectively. Those strains with salt optima significantly below 10% (w/v) salinity formed three major clusters. The first included strains of E. mobilis and E. marismortui. The second cluster contained strains of E. shaposhnikovii, E. vacuolata and one strain that had been tentatively identified as E. mobilis but should be considered as a strain of E. shaposhnikovii. The third group contained strains that were assigned to E. mobilis but should be regarded as a separate and new species. The observed similarities support and extend patterns of relationships obtained by other taxonomic investigations on the basis of a smaller number of strains.

Description: The dynamics of the coastal ocean along the southeastern coast of Africa is dominated by a strong and intense western boundary current, the Agulhas Current. With a near-uniform, narrow continental shelf and a steep shelf slope that stabilizes this current, the trajectory of the Agulhas exhibits great stability. The only substantial perturbation occurs with the irregular passage of a Natal Pulse, a soliton meander. The initiation of this meander at the Natal Bight is due to a barotropic instability when the intensity of the landward border of the current exceeds a certain threshold value. This may come about with natural fluctuations in the current or with the adsorption of deep-sea eddies onto the current. Under a climate change scenario of altered wind stress curl over the South Indian Ocean it is conceivable that the threshold for the triggering of a Natal Pulse will occur more frequently. This will lead to a situation where the current axis on average lies further offshore. The possible consequences of such a situation on the rainfall of the coast, on the ecology of estuaries and the coastal ocean, and on the socio-economics of the region is discussed.

Description: The deep-sea borehole seal CORK was deployed for the first time on a modern accretionary prism during ODP Leg 146 to the Cascadia Margin. Ten months after the deployment the fluid flow and geochemistry of the borehole fluids was investigated during several dives by DSRV Alvin. The chemical analysis of the borehole fluids revealed methane concentrations of more than 3.5 mM, whereas oxygen and dissolved ions as Cl, NO3, or PO4 are still close to the ambient seawater composition. The exceedingly high methane content measured at the top of the sealed borehole and the observed degassing during the ascent of the submersible indicates that the sampled fluid was initially saturated or close to saturation with respect to CH4. The hydrocarbons are characterized by ratios of 170–200 and δ13C values of − 59.5 to − 62.4%o which indicates a considerable admixture of thermogenic hydrocarbon gases. The occurrence of methane of partly thermogenic origin demonstrates that CH4 enters the sealed borehole in the lower, perforated section (94–178 mbsf) and accumulates at the top of the borehole. This suggests the occurrence of free gas within the encapsulated borehole. Considering the stability field of CH4-hydrates, the formation of these ice-like structures may take place and potentially results in a clogging of the top of the borehole. Such precipitates could result in a decoupling of the top of the borehole from the hydraulic and geochemical regime of the accretionary complex, an important aspect for future plans of CORK deployments.

Description: We review and evaluate the design and operation of twenty-seven known autonomous benthic chamber and profiling lander instruments. We have made a detailed comparison of the different existing lander designs and discuss the relative strengths and weaknesses of each. Every aspect of a lander deployment, from preparation and launch to recovery and sample treatment is presented and compared. It is our intention that this publication will make it easier for future lander builders to choose a design suitable for their needs and to avoid unnecessary mistakes.

Description: Hydrographic and tracer [chlorofluorocarbon (CFC), component F11] data in the tropical Atlantic off Brazil taken in spring 1994 are used to describe the development of the water mass characteristics of Antarctic Bottom Water (AABW) between 10 degrees S and 11 degrees N. To compute the AABW transports, geostrophic computations and directly measured velocity fields are combined. Velocity profiles were measured with the Pegasus profiling system and an ADCP attached to the CTD. The F11 increase from 10 degrees S to 11 degrees N, mainly in the upper part of the tracer-poor AABW, reveals the mixing of AABW along its path with the overlying North Atlantic Deep Water, which carries a significant F11 signal in the equatorial Atlantic. While propagating north of 5 degrees S, the AABW shifts to higher salinities at a given temperature. About one-third of the northward flowing AABW at 10 degrees S (4.8 Sv) and at 5 degrees S (4.7 Sv) west of about 31 degrees 30'W enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35 degrees W (1.5-1.8 Sv). The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40 degrees W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise (2.2 Sv). At 44 degrees W, north of the Ceara Rise, AABW flows west in the interior of the basin in a main core near 7 degrees 15'N (1.9 Sv). A net return how of about 0.5 Sv was found north of 8 degrees 43'N. A large fraction of the AABW (1.1 Sv) enters the eastern Atlantic through the Vema Fracture Zone, leaving only 0.3 Sv of AABW for the western Atlantic basins

Description: We compare the time series of major element geochemical and Pb- and Nd-isotopic composition obtained for seven hydrogenous ferromanganese crusts from the Atlantic, Indian, and Pacific Oceans which cover the last 60 Myr. Average crust growth rates and age-depth relationships were determined directly for the last about 10 Myr using Be-10/Be-9 profiles. In the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial Be-10/Be-9 ratios due to the lack of additional information. Co contents have also been used previously to estimate growth rates in Co-rich Pacific and Atlantic seamount crusts (Puteanus and Halbach, 1988). A comparison of Be-10/Be-9- and Co-based dating of three Co-rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated Be-10/Be-9-based growth rates back to 60 Ma. Our data show that the flux of Co into Co-poor crusts has been considerably lower. The relationship between growth rate and Co content for the Co-poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits (Manheim, 1986). The results suggest that the Co content provides detailed information on the growth history of ferromanganese crusts, particularly prior to 10-12 Ma where the Be-10-based method is not applicable. The distributions of Pb and Nd isotopes in the deep oceans over the last 60 Myr are expected to be controlled by two main factors: (a) variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and (b) variability of supply rates or provenance of detrital material delivered to the ocean, linked to climate change (glaciations) or major tectonic uplift. The major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust. Consequently, any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution. This is because local processes appear to have dominated over more basin wide paleoceanographic effects. In this study Co is the only element which shows a relationship to Pb and Nd isotopes in Pacific crusts. A possible link to changes of Pacific deep water properties associated with an enhanced northward advection of Antarctic bottom water from about 14 Ma is consistent with the Pb but not with the Nd isotopic results. The self-consistent profiles of the Pb and Nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts, including phosphatization events, have been insignificant for particle reactive elements such as Pb, Be, and Nd. Isotope time series of Pb and Nd show no systematic relationships with major element contents of the crusts, which supports their use as tracers of paleo-seawater isotopic composition

Description: Variations of intensity and composition of biogenic particle flux at the northern boundary of the present PolarFrontal Zone in the Atlantic sector of the Southern Ocean are indicators of major changes of paleoenvironmentalconditions on glacial/interglacial time scales during the Late Quaternary. In order to estimate those pastchanges, sediment accumulation patterns of two piston cores, one from just north and one just south of thepresent day position of the Subantarctic Front were reconstructed. Using the 230Thex method large contributionsof laterally supplied material were quantified and used to correct sediment accumulation rates. During the lastglacial focussing of biogenic opal-dominated material exceeded the original contribution from the surfacewater above by a maximum factor of 8.7. The initial activity ratio of 231Paex/230Thex was used as tracer forbiogenic particle flux and composition and indicates that during the glacial stages 2 and 4 the area of high opalproductivity was situated above the location of the southern core whereas the northern core has not beenreached by this northward shift during the last 130 kyr as shown by the pattern of focussing-corrected bulkaccumulation rates. If the position of the Antarctic Polar Front has remained at the northern boundary of thehigh opal productivity area during the last 130 kyr, the results suggest that was located exactly between thetwo core sites during glacial stages 2 and 4. A two-box modeling approach involving particle flux and boundaryscavenging intensity of 231Pa was applied to estimate the possible range of the 231Paex/230Thex ratio recordedin Southern Ocean sediments. Previous estimates on the export of 231Pa from the Atlantic into the SouthernOcean are corroborated but the model suggests a low sensitivity of the 231Paex/230Thex ratio in Southern Oceansediments to variations of the residence time of North Atlantic Deep Water in the Atlantic Ocean.

Description: The sediments recovered on ODP Leg 104 have been reported to be characterized by hiatuses. The hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity. They have been associated with major paleoenvironmental changes, reorganization of global deep water production, and increased bottom water flows. Because of the importance of hiatuses for ongoing research, we decided to closely investigate the sedimentation history for the most significant Pliocene and Miocene biostratigraphic hiatuses by sedimentologic and geochemical means. The sedimentologic studies include clay mineral distributions, grain size data, and organic carbon concentrations. The geochemical studies include determination of Full-size image (〈1 K)Sr ratios, 10Be and Ir concentrations. The results of the sedimentologic studies suggest either that paleoenvironmental changes associated with hiatuses are not represented in the preserved sediments, or that the hiatuses are an artifact of interpretation of the biostratigraphic data. Strontium isotopes indicate continuous sedimentation for the interval investigated at Site 642, an interpretation confirmed by the steady decline in 10Be. Full-size image (〈1 K)Sr ratios in the interval from above and below proposed hiatuses H Full-size image (〈1 K) and Full-size image (〈1 K) at Site 643 display stronger changes with depth than expected by steady sedimentation. Ir data for this same interval indicate reduced sedimentation rates. Combining both, sedimentologic and geochemical evidence, the proposed hiatuses could not be confirmed and may represent preservation artifacts.

Description: Small-scale features of the Antarctic Circumpolar Current (ACC) along a meridional section at 6°W between the Polar Front and the ACC-Weddell Gyre Boundary Front are discussed using data collected during the austral spring cruise ANT X/6 of R. V. Polarstern organized within the framework of the European IGBP-JGOFS (Southern Ocean). The section covered three distinct fronts, namely the Polar Front, the Southern Polar Front (also Southern ACC Front), and the ACC-Weddell Gyre Boundary Front. Physical measurements during repeated transects over a period of 6 weeks in October/November revealed a large variability in the Polar Frontal region, indicating meandering and eddy shedding. The positions of the Southern Polar Front and the ACC-Weddell Gyre Boundary Front were observed to be far more stable than that of the Polar Front. A possible reconstruction of the meandering flow field near the Polar Front, based upon the physical observations, is presented. Details in the flow field coincide with the spatial distribution of a number of biological parameters such as phytoplankton biomass and species, and photosynthetic pigments. Although a causal relationship between them is likely, biomass enhancement cannot be understood simply in terms of macronutrients from deeper layers entering the euphotic zone, as substantiated for other oceanic frontal regions, because macronutrients do not limit phytoplankton blooms. This process, however, can be important for the micronutrient iron. Evidence is presented that the Antarctic Zone of the ACC can be subdivided into a number of spheres of influence related to the fronts. Interleaving of water is apparent between positions within such a region, but not between the regions.

Description: The Foundation Seamounts form a 1400 km-long chain on the Pacific plate from 32 °S, 127 °W to the Pacific-Antarctic spreading axis at 38 °S, 111 °W. Previously only known from sparse single-beam echosoundings and satellite altimetry, we present here the first multibeam bathymetric survey and geological sampling results. We confirm that the submarine topography correlates with the altimetry, and that the chain is volcanic rather than tectonic or microcontinental in origin. The chain can be divided up morphologically and geochemically into three section: (1) west of 125 °W large flat-topped volcanoes composed of incompatible-element depleted lavas ( ≈ 1) of a near-ridge origin with little or no plume influence, (2) between 125 and 115 °W true intraplate volcanoes with incompatible element enrichment ( 〉 1.9) generated over the Foundation plume, (3) east of 115 °W E-W-trending volcanic ridges with compositions ( 2.0-0.3) suggestive of interaction between the plume and the Pacific-Antarctic spreading axis. On the spreading axis moderate incompatible element enrichments ( ≈0.8, cf. ≈ 0.3 outside the Foundation area) also suggest plume influence. It appears that the activity of the Foundation plume in the last few million years has (1) significantly waned and (2) become wholly channeled towards the spreading axis. The Foundation plume may be in the process of “dying”.

Description: Tens of thousands of synthetic substances are in existence today and hundreds of new compounds are being introduced every year. Because of the complexity of the physico-chemical interactions between pollutants and the marine environment, the potential toxicity of contaminants can be assessed adequately only by means of bioassays with living organisms. From a practical point of view, a bioassay needs to be sensitive and scientifically valid, yield rapid results at moderate cost, and the organism in question must be readily available. Ecotoxicological bioassays with bivalve embryos and larvae fulfil these criteria better than most other tests. They have increasingly come into use during the past three decades and are now commonly employed to ascertain the biological effects of pure chemicals, as well as to determine the quality of effluents, coastal waters and sediments sampled in the field. There do not appear to be very great differences between bivalve species with regard to larval sensitivity to toxicants. The principal species for bioassays are oysters (Crassostrea gigas and C. virginica), and mussels (Mytilus edulis and M. galloprovincialis). Bioassays are conducted with gametes and larvae of ail ages: sperm and unfertilized eggs, embryos, young D-larvae, intermediate umboned larvae, and pediveligers towards the end ofthe pelagic period. Embryos are usually the most sensitive stage. Recent advances now also permit bioassays on metamorphosing pediveligers, a method particularly suited to investigate the effects of adsorbate-contaminated surfaces. There are various criteria for the assessment oftoxic effects, including embryogenesis success (abnormalities), larval growth, mortality, physiology (e.g. feeding or swimming activity), and metamorphosis success. Chronic toxicity studies may be carried out over periods ofseveral weeks, but larval rearing in the laboratory requires considerable effort (e.g. cultivation of algal food). The method of choice for investigations of acute toxicity and for routine monitoring studies is the embryo bioassay because it is very sensitive, relatively simple, and produces results within 24 or 48 hours. The data obtained by different investigators are often difficult to compare, however, because of differences in methodology. There is no firmly established procedure, and further simplification and standardization of techniques is required. In bioassays with a single pollutant, the effective toxic concentration may span several orders of magnitude, depending on bioassay procedures, larval stage and choice of response. Tributyl-tin (TBT) is the most toxic compound ever bioassayed with bivalve larvae, with effective concentrations (EC50) as low as a few nanograms per litre (i.e. 10−3 ppb). Heavy metals (particularly mercury, silver and copper) are next in order of toxicity, with EC50 values between a few micrograms per litre (ppb) and several hundred ppb. Chlorine and some organochlorine pesticides may also have EC50 values of less than 100 ppb, while detergents and petroleum products are generally less toxic

Description: Though many studies on the Mg contents in the calcitic tests of foraminifers exist, the processes controlling its uptake are still a matter of debate. Laboratory cultures offer an excellent opportunity to reveal these mechanisms. The Mg concentrations within single chambers of the planktic foraminifer Globigerinoides sacculifer (BRADY) maintained under controlled laboratory conditions were measured (1) at variable temperatures (19.5–29.5 °C) and constant salinity and (2) at variable salinity (22–45‰) and constant temperature. The experimental results suggest that under natural conditions, temperature is the leading mechanism controlling the Mg/Ca ratio. Temperature and magnesium are related proportionally. A temperature increase of ca. 10 °C gives rise to an increase of the magnesium concentrations of ca. 130%. Drastic (unnatural) salinity changes dominate the effects of temperature. A 110% change in the Mg/Ca ratio was observed when salinity was elevated or reduced by more than ca. 10‰. Specimens which underwent gametogenesis reveal significantly higher Mg concentrations than specimens that did not release gametes. Partition coefficients for Mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite. When comparing observed Mg/Ca ratios of foraminiferal tests with predicted Mg/Ca ratios calculated according to empirical equations, it becomes evident that foraminiferal tests are undersaturated with respect to Mg for the water temperature they have experienced. Apparently, foraminifers are capable of controlling their Mg concentration. The physiological processes presumably responsible for such depressed Mg/Ca ratios appear to be temperature-controlled as deduced from the close relationship of the observed Mg/Ca ratios and water temperature. This study demonstrates that variations in temperature and salinity are definitely reflected in the Mg content of foraminiferal tests. Magnesium may thus serve as a paleo-proxy for past surface water temperatures, as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded.

Description: High resolution 230Thex and 10Be and biogenic barium profiles were measured at three sediment gravity cores (length 605–850 cm) from the Weddell Sea continental margin. Applying the 230Thex dating method, average sedimentation rates of 3 cm/kyr for the two cores from the South Orkney Slope and of 2.4 cm/kyr for the core from the eastern Weddell Sea were determined and compared to δ18O and lithostratigraphic results. Strong variations in the radionuclide concentrations in the sediments resembling the glacial/interglacial pattern of the δ18O stratigraphy and the 10Be stratigraphy of high northern latitudes were used for establishing a chronostratigraphy. Biogenic Ba shows a pattern similar to the radionuclide profiles, suggesting that both records were influenced by increased paleoproductivity at the beginning of the interglacials. However, 230Thex0 fluxes (0 stands for initial) exceeding production by up to a factor of 4 suggest that sediment redistribution processes, linked to variations in bottom water current velocity, played the major role in controlling the radionuclide and biogenic barium deposition during isotope stages 5e and 1. The correction for sediment focusing makes the ‘true’ vertical paleoproductivity rates, deduced from the fluxes of proxy tracers like biogenic barium, much lower than previously estimated. Very low 230Thex0 concentrations and fluxes during isotope stage 6 were probably caused by rapid deposition of older, resedimented material, delivered to the Weddell Sea continental slopes by the grounded ice shelves and contemporaneous erosion of particles originating from the water column.

Description: Recent measurements indicate the transatlantic extent of the Namib Col Current at depths of 1300-3000 m near Lat. 22 degrees S in the South Atlantic Ocean. This current forms a continuous circulation structure from the Namib Col on the Walvis Ridge to the western trough, though its characteristic change as deepwater with varying properties enters and leaves the current owing to a meridional flow component. Transport estimates from hydrographic sections on the Walvis Ridge and at 15 degrees W near the crest of the Mid-Atlantic Ridge indicate a strength of about 3 x 10(6) m(3) s(-1) The current is part of a larger-scale eastward Row at Lon. 25 degrees W; transport estimates across the salinity maximum core there show a similar strength. Associated with this high-salinity high-oxygen current is a basin-wide front in these properties of varying intensity (weaker in the east) marking the transition to deep water whose North Atlantic characteristics have been partly erased by mixing with Circumpolar Deep Water in the southwest South Atlantic. The water which finally crosses the Walvis Ridge is supplied both by the eastward flow of this (diluted) North Atlantic Deep Water and by a general southeastward interior flow from the northern Angola Basin. Evidence suggests that this deep water continues south in the eastern Cape Basin, leaving the South Atlantic near the African continent.

Description: A data assimilation system has been developed which has been used in conjunction with a primitive equation model of the tropical Pacific. The assimilation system is based on a time weighted successive correction method. The data are inserted continuously by updating the model solution every time step. The inserted data are taken from a time window, centered on the present model time step. Three experiments were performed. In the first assimilation run, SST observations were assimilated. In the second experiment, island based sea level observations were assimilated, while in the third run subsurface temperature data were assimilated. An intercomparison between the three assimilation runs was made and we discuss two questions. First, to which extent can the model fields be improved, and second, how long is the assimilated information retained by the ocean model.

Description: Sensitivities of cirrus cloud radiative forcing as well as solar albedo and infrared emittances to ice crystal size spectrum and ice crystal shape were examined using a coupled cloud-radiation model. The single- and bi-modal crystal size distribution were considered and simulated based on field measurements. Optical parameters of ice crystals shaped as hexagonal columns and random polycrystals (being frequently found in cirrus clouds) were calculated with a ray-tracing method. Both solar and infrared cirrus radiative forcing are influenced by the pattern of crystal size spectra. The net radiative forcing is lower for bi-modal than for single-modal spectra. The solar radiative forcing of cirrus cloud is reduced by nonspherical ice crystals, due to larger albedo effects of nonspherical crystals compared to those of equivalent spherical crystals. Moreover, this reduction in solar radiative forcing by random polycrystals is even larger than that by hexagonal column crystals. The cloud radiative forcing, solar albedo and infrared emittance are changed significantly as the mean crystal size approaches the smaller size end. Furthermore, net cloud radiative forcing is positive in most cirrus cases. Exceptions are cirrus clouds with a large number (〉107 m−3) of small (mean maximum dimension 〈30 μm) ice crystals and cirrus clouds with bi-modal crystal size distribution and large particle size for the second maximum peak.

Description: In the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning the input of phytodetrital matter to the seafloor; phospholipids were analyzed to estimate the total biomass of small benthic organisms (including bacteria, fungi, flagellata, protozoa and small metazoan meiofauna). A new term `small size class biomass' (SSCB) is introduced for the biomass of the smallest size classes of sediment-inhabiting organisms; the reduction of fluorescein-di-acetate (FDA) was determined to evaluate the potential activity of ester-cleaving bacterial exoenzymes in the sediment samples. At all stations benthic biomass was predominantly composed of the small size spectrum (90% on the shelf; 97–98% in the bathyal and abyssal parts of the transect). Small size class biomass (integrated over a 10 cm sediment column) ranged from 8 g C m−2 on the shelf to 2.1 g C m−2 on the adjacent Porcupine Abyssal Plain, exponentially decreasing with increasing water depth. However, a correlation between water depth and SSCB, macrofauna biomass as well as metazoan meiofauna biomass exhibited a significantly flatter slope for the small size classes in comparison to the larger organisms. CPE values indicated a pronounced seasonal cycle on the shelf and upper slope with twin peaks of phytodetrital deposition in mid spring and late summer. The deeper stations seem to receive a single annual flux maximum in late summer. SSCB and heterotrophic activity are significantly correlated to the amount of sediment-bound pigments. Seasonality in pigment concentrations is clearly followed by SSCB and activity. In contrast to macro- and megafauna which integrate over larger periods (months/years), the small benthic size classes, namely bacteria and foraminifera, proved to be the most reactive potential of the benthic communities to any perturbations on short time scales (days/weeks). The small size classes, therefore, occupy a key role in early diagenetic processes.

Description: Colonization of new habitats, which have been established as a result of a catastrophic disturbance of the environment, is one of the characteristic repetitive events throughout the Phanerozoic. In recent years, much attention has been paid to investigations focusing on biological recovery of benthic habitats severely disturbed by human activity. In order to improve our environmental and stratigraphical interpretations of such events, we need a more thorough understanding of the processes involved in colonization by one of the most abundant and useful fossil groups, the benthic foraminifera. The present review focuses on processes governing benthic foraminiferal dispersion and colonization patterns in modern environments. For benthic foraminifera, the only active dispersal mechanism is through self-locomotion on or within the sediment and this is considered to be efficient over short distances only. Several passive dispersal methods have been suggested but two seem to be of more general importance. These are dispersal through release and transport of embryonic juveniles and passive suspension and transport of various growth stages. Both are probably important for most benthic foraminifera but the former is likely to be the main mechanism for attached, tubular and larger foraminifera, which are not easily entrained at a later life stage. The latter seems to be a more important dispersion mechanism for benthic foraminifera than previously realized. The colonization rate of soft-bottom substrates is closely related to the hydraulic regime in, and the transit time from, the source area inhabited by species capable of colonizing the new habitat (as long as food and other environmental characteristics are not limiting factors). The transit time depends on the speed of the transporting medium and the distance from the source area. There seems to be two end-processes which can operate during the colonization, depending on whether physically induced or biological processes are allowed to dominate. They are characterized by different colonization patterns. In high energy environments (bottom current velocities often 〉20 cm/s), a short transit time may cause the major components of the nearest ambient seafloor assemblages to colonize the new habitat within days. In this case the colonization is simply through a physical transfer of parts of the source community to the new habitat, allowing no time for pioneer, opportunistic assemblages to develop. In low energy environments (bottom current velocities generally 〈10 cm/s), the transit time is long for most species. Here, colonization follows the classic metazoan successional pattern with an initial, high abundance pioneer assemblage strongly dominated by small opportunists followed by development of assemblages with increasing numbers of specialized species and recovery can take from one to several years. Initial lack of food (e.g., volcanic ash) or `hostile' substrate properties (e.g., recently reoxygenated or severely contaminated sediments) may delay colonization by months or even years. Small, infaunal species (both calcareous and agglutinated) are among the first and most successful colonizers of soft bottom habitats from shallow waters to the deep sea. Throchospiral agglutinated taxa are among the most abundant colonizers on deep sea hard substrates.

Description: The Skagerrak basin is a deep water extension of the North Sea. It is of particular interest as an analogue for past epicontintal shelf basins because it presents environmental contrasts with the adjacent shelf seas. In this study the distribution patterns of benthic foraminifera have been used to infer taphonomic and oceanographic processes. Only by separating living from dead assemblages is it possible to interpret taphonomic changes. The transport of foraminiferal tests to the Danish slope is inferred from the presence there of dead exotic tests whose provenance is considered to be from the south. The abundance of detrital organic matter on the Danish slope is likewise inferred to be sourced from the same direction. Thus, the Danish slope is interpreted to be a depositional sink. Apart from transport, another taphonomic process is the dissolution of calcareous tests. This is clearly demonstrated both by the fragility of some tests as viewed under the microscope and by the disparity between the composition of the living and dead factor associations. In the deep basin in particular, the two predominantly calcareous living associations are replaced by a single predominantly agglutinated dead association due to carbonate dissolution. The Danish slope of the Skagerrak Basin is demonstrated to be an area of high benthic fertility. This is based on the high density of living (stained) benthic foraminifera (comparable with that of the Mississippi delta), particularly the abundance of Stainforthia fusiformis, an opportunistic species, and tubular agglutinated forms. The fertility is linked with the high abundance of particulate organic matter here. Previous regional studies have focused on total (living plus dead) distributions of 〉 100 or 〉 125 μm sized foraminifera. These factor assemblages are distinct from the 〉63 μm living and dead associations described here.

Description: Despite the large decline in Northern Hemisphere summer insolation during the last 8000 years, neither sea level nor polar temperatures have as yet undergone any significant downturn. This behavior is consistent with the prediction by Kukla and Matthews (1972) that the Holocene interglacial will terminate suddenly with a jump to another of the climate system's modes of operation. This is what happened at the end of the last period of peak interglaciation. However, complicating the situation is evidence that ice sheet growth during the transition from marine stage 5e to 5d preceded the shut down of the Atlantic's conveyor circulation which is thought to have brought Europe's Eemian to a close. If so, then in the natural course of events, the end of the present interglaciation awaits the onset of ice cap growth. However, it must be kept in mind that the ongoing buildup of greenhouse gases may alter the natural course of events. In particular, the warming and wetting of the planet will gradually reduce the density of surface waters in the regions where deep waters form. As this reduction is not likely to be symmetrical between the northern Atlantic and the margin of the Antarctic continent, the current near balance between deep water production in the north and south may be disrupted causing an abrupt reorganization of the ocean's thermohaline circulation. Based on the paleoclimatic record, such a reorganization would have had a profound impact on the planet's climate.

Description: The squid Loligo opalescens (Cephalopoda, Mollusca) was reared in artificial sea water in a closed system consisting of two 1300-l circular tanks. When the squids reached mantle lengths of 20 to 30 mm, they were transferred to a 10 000-l closed system raceway. From hatching, mantle length increased exponentially at a mean rate of 1.69% per day throughout the experiment. The largest and longest-lived squid attained a maximal size of 77 mm mantle length in 8 months. Only live food organisms, which consisted of copepods, other crustaceans and fishes, were accepted by the squids. Mortality, attributed to starvation and fin damage, was greatest during the first 20 days and again between days 45 and 70.

Description: Faunal structure is described for the planktonic molluscs of the Middle Atlantic Bight based on two years of seasonal data from the continental shelf. Collection and taxa groups are constructed using numerical classification and reciprocal averaging ordination. Discriminant analysis is used to relate surface collection groups to physical variables, then taxa group distribution among these collection groups is analyzed by nodal fidelity analysis. The areal distribution of dominant species is presented by season, as is their surface temperature-salinity distribution. Four communities are recognized on the continental shelf. A subarctic community, including Limacina retroversa, Paedoclione doliiformis, and Clione limacina, is advected down the central shelf region from the northeast. A Gulf Stream community of weak vertical migrators, including Limacina trochiformis, Cavolinia longirostris, Creseis conica, Atlanta peroni, and A. gaudichaudi, is introduced onto the shelf in occasional intrusions across the shelf-edge front. A depth-limited warm-water community of strong vertical migrators, including Limacina inflata, L. bulimoides, L. lesueuri, and Cavolinia inflexa is generally confined offshore of the 100-m isobath since the extent of their daily vertical migration is greater than the bottom depths on the continental shelf. A coastal community, including the larvae of Loligo pealei and of Ensis directus is found in coastal water of local origin and is generally confined within a coastal boundary layer.

Description: Microbial secondary metabolites are useful high value products that are normally produced by liquid culture; but could be advantageously produced by solid-state fermentation (SSF). Particularly if SSF could benefit from a deeper understanding of microbial physiology in a solid environment. Recent research indicates that different kind of secondary metabolites can be produced by SSF: antibiotics, phytohormones, food grade pigments, alkaloids, etc. Physiology in SSF shows several similarities with physiology in liquid medium, so similar strategies must be adapted for efficient processes. However, there are certain particularities of idiophase in solid medium which dictate the need for special strains.

Description: The cause of the climatically controlled fluctuations in the carbonate content of deep-sea sediments remains the subject of uncertainty and debate. Three variables are involved: supply of biogenic carbonate, loss by dissolution, and dilution by non-carbonate phases. It is suggested that 230Th, which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale. Results of a preliminary analysis based on published data indicate that, for depths at and above the lysocline, the carbonate fluctuations observed in cores from the North Atlantic Ocean are due primarily to variations in the terrigenous clay input, which was 2–5 times higher during glacials than during interglacials. Carbonate deposition appears to have been somewhat reduced during glacials, but probably not by more than a factor of 2. From published 230Th232Th profiles it appears that the South Atlantic Ocean also received increased inputs of terrigenous clay during glacial periods.

Description: Microbial secondary metabolites are useful high value products that are normally produced by liquid culture; but could be advantageously produced by solid-state fermentation (SSF). Particularly if SSF could benefit from a deeper understanding of microbial physiology in a solid environment. Recent research indicates that different kind of secondary metabolites can be produced by SSF: antibiotics, phytohormones, food grade pigments, alkaloids, etc. Physiology in SSF shows several similarities with physiology in liquid medium, so similar strategies must be adapted for efficient processes. However, there are certain particularities of idiophase in solid medium which dictate the need for special strains.

Description: An overview is provided of time-independent physical/chemical properties as related to crystal structures. The following two points are illustrated in this review:  (1) Physical and chemical properties of structure I (sI) and structure II (sII) hydrates are well-defined; measurements have begun on sH. Properties of sI and sII are determined by the molecular structures, described by three heuristics:  (i) Mechanical properties approximate those of ice, perhaps because hydrates are 85 mol % water. Yet each volume of hydrate may contain as much as 180 volumes (STP) of the hydrate-forming species. (ii) Phase equilibrium is set by the size ratio of guest molecules within host cages, and three-phase (Lw−H−V) equilibrium pressure depends exponentially upon temperature. (iii) Heats of formation are set by the hydrogen-bonded crystals and are reasonably constant within a range of guest sizes. (2) Fundamental research challenges are (a) to routinely measure the hydrate phase (via diffraction, NMR, Raman, etc.), and (b) to formulate an acceptable model for hydrate formation kinetics. The reader may wish to investigate details of this review further, via references contained in several recent monographs.

Description: The accumulation rates (AR) of coarse (〉 63 μm) terrigenous material in the Norwegian-Greenland Sea (NGS) were investigated for the last ca. 200 kyr. Comparisons of accumulation rates in the northern, western and eastern NGS show different histories. The highest AR peak in the eastern NGS occurs near the beginning of Stage 6 (183 ka); this peak may signal the rapid growth and deterioration of the Scandinavian Ice Sheet. An AR peak in the northern NGS at the Stage 6/5 transition (Termination II; 128 ka) may signal the decay of the Barents Sea Ice Sheet. The highest peak in the western NGS occurs during the Stage 2/1 transition (Termination I; 13.6 ka); due to its location near the East Greenland Current, correlation with ice sheets is difficult. Comparisons of the AR data from the eastern NGS with terrestrial data from Scandinavia demonstrate a clear link between glacial advances/retreats and accumulation rates of coarse-grained material in the deep ocean: the retreat of tidewater ice fronts correlates with high ARs. Thus marine data can be used to determine the movement history of continental ice sheets.

Description: DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504 B in a 260 m-thick ooze—chalk—limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW m−2). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries.

Description: Glass separates from 115 ash layers derived from the Kamchatkan (DSDP Site 192; 34 layers), the eastern Aleutian (DSDP Site 183; 56 layers) and the Alaska Peninsula (DSDP Site 178; 25 layers) volcanic arcs have been analyzed for up to 28 elements. In addition, the abundance and diversity of associated mafic phenocrysts have been evaluated. The resulting data set has made possible an evaluation of the late Miocene to Recent changes in composition of ashes derived from North Pacific volcanic arcs and of the factors controlling the evolution of highly siliceous magmas. We find no evidence for a general transition from arc tholeiite to calc-alkalic magma parentage of ashes derived from the volcanic arcs during the last 10 m.y., but instead find 0.1- to 0.5-m.y. intervals during which particular types of volcanism are prevalent. Most convincing is the transition from arc tholeiite to calc-alkalic for ashes derived from Kamchatka during the last 0.8 m.y., a change believed to be associated with a landward shift in the site of magma generation. Considered together, ashes derived from North Pacific volcanic arcs have been becoming more siliceous during the last 1.5 m.y. and may be associated with accelerated subduction during the same time interval. Hydrous phenocrysts (e.g., biotite) are typically associated with low-silica deep-sea ashes, but not with terrestrial volcanic rocks of comparable silica contents, suggesting the important role of water in the evolution of siliceous magma. REE patterns and relative abundances of mafic phenocrysts demonstrate the importance of fractional crystallization in controlling the evolution of highly siliceous arc magmas. REE increase with increasing silica, but become less concentrated in ashes with SiO2 〉 64%. Eu anomalies increase throughout the SiO2 range. Initial fractionation is dominated by clinopyroxene and plagioclase with amphibole strongly influencing fractionation above 64% SiO2.

Description: Petrographic examination of amygdules and veins associated with moderately altered pillow basalts dredged from the Peru Trench has revealed that a consistent pattern of mineral crystallization has occurred. This sequence is: (1) green, weakly pleochroic clay (R.I. 〉 1.56); (2) dark yellowish brown, non-pleochroic clay (R.I. 〉 1.56); (3) light yellowish brown to colorless, fibrous, weakly pleochroic clay (R.I. 〈 1.56); and (4) calcite or celadonite. Chemical and X-ray diffraction analyses suggest that all clay mineral amygdule and vein fillings are dominated by intimate mixtures of an Fe-rich saponite and nontronite with very small admixtures of serpentine and illite. It is argued that sequential mineral fillings of fractures and vesicles may provide significant information about the chemistry of circulating interstitial fluids. For the pillow basalts studied the first-formed clays were enriched in nontronite, thereby suggesting Fe-rich fluids. These in turn were followed by saponite-rich clays and calcite. The change from Fe-and Mg-rich fluids to dominantly Ca-rich fluids is thought to correspond to a change from mafic mineral alteration to plagioclase alteration in the pillow basalts. An increase in the Fe3+/Fe2+ ratio of clays toward the centers of vesicles may indicate a change toward a more oxidizing environment of alteration.

Description: Five separate exposures of oceanic basalts were dredged in the vicinity of the Peru-Chile Trench between 9° and 27°S latitude. Each dredge is dominated by abundant pillow basalts. Approximately ten of the most unaltered, glassy and fine-grained samples were selected for detailed chemical and petrographic analyses from each dredge area. All basalts recovered in the Peru-Chile Trench are olivine and quartz-normative tholeiites that are believed to have formed at the now extinct Galapagos Rise 30–50 m.y. ago. Detailed chemical analyses of the basalts, including major and selected trace and rare earth elements, indicate that considerable compositional variability exists both within each of the dredged areas as well as between areas. Most of the inherent chemical variability observed within particular basement sections appears consistent with the concept of temporal evolution of magma bodies at a former spreading center by shallow-level fractional crystallization involving primarily plagioclase and olivine. In contrast, important chemical differences between the dredged areas suggest compositional heterogeneities in the mantle source regions. Our results indicate that although shallow-level fractionation has brought about large changes in composition of basalts in each area, compositional trends are distinct and appear to reflect original mantle-derived compositional differences.

Description: Thirty-four ash layers of Pleistocene and Pliocene age from DSDP Site 192, northwestern Pacific Ocean, have been subjected to detailed chemical and optical study to evaluate: (1) the chemical and optical variability in glass shards from deep-sea ash layers, and (2) secondary changes brought about by prolonged exposure to seawater. Glass shards from approximately half of the ash layers studied were found to have uniform compositions which approach the precision of the microprobe chemical analyses, whereas the remainder are compositionally diverse (e.g., SiO2, variations of 5–15% among shards from the same ash layer) and appear to be the eruptive products of compositionally zoned magma chambers. Optical studies of glass shards confirm the absence of devitrification or the formation of pervasive secondary alteration products. By contrast, chemical studies suggest that the glass shards have experienced progressive hydration with possible minor ion exchange of K, Mg, Ca and Si. The hydration occurs rapidly and leads to a rather uniform water content of 4.5–5% after several hundred thousands of years exposure to seawater. Step-wise heating dehydration experiments, optical effects, and published'oxygen isotope studies indicate that the water of hydration is incorporated uniformly within the glass. Systematic chemical differences between electron microprobe analyses of glass shard interiors and corresponding bulk chemical study by atomic absorption lead us to postulate that glass shard margins have undergone a minor chemical exchange with major cations in seawater. They have gained 0.10–0.20 wt. % K20, MgO, and CaO while losing a corresponding amount of Si2O. Although the glass shards from DSDP Site 192 are hydrated and may have experienced subtle, surficial ion exchange, we stress that they are the most chemically representative samples available of magmas that were explosively erupted from volcanic arcs.

Description: A complete set of linearly independent relationships among the different cross spectral components obtained from pairs of moored instruments is derived which can be utilized to test whether or not the observed fluctuations within the internal wave frequency band represent a field of propagating internal waves. A further complete set of relationships is derived which enables to test whether or not the internal wave field is horizontally isotropic and (or) vertically symmetric. These relations are compared with corresponding relations for alternative models (standing internal wave modes, three-dimensional isotropic turbulence) and their capability to discriminate between the various models is investigated. The tests are applied to a set of data for which it is found that the observed fluctuations are consistent with both propagating and standing internal waves whereas isotropic turbulence must be rejected for the most part of the internal wave frequency band.

Description: Data from the Nansen Basin of the Arctic Ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer Neogloboquadrina pachyderma (sin.) calcifies. The vertical distribution of δ18O values of net-sampled speciments, together with their abundances and proportion of calcification, are compared with δ18O values from both water samples and foraminiferal tests from core-top sediments. Within the Nansen Basin the average depth of habitat of N. pachyderma (sin.) changes from about 150 m in the southern part to about 80 m in the northern. The average depth of calcification, however, in both regimes varies between 100 and 200 m water depth. δ18O data from net sampled N. pachyderma (sin.) are directly reflected in the core-top sediment data, but compared to equilibrium calcite δ18O values derived from measurements of the ambient water, a consistent offset of about 1‰ over all depth intervals is observed. While in the southern part of the Nansen Basin advection through Fram Strait of planktic foraminifers from further south may play a role, the data from the northern part of the Nansen Basin give clear evidence that the observed offset in δ18O values is caused by a vital effect of N. pachyderma (sin.).

Description: The excretion of siderophores and the reduction of organic iron-complexes at the cell surface are common reactions of terrestrial plants, fungi and bacteria in response to low availability of iron. However, there is much less evidence for the use of these strategies by marine phytoplankton. It has been argued that siderophore excretion is inefficient in an aquatic environment due to rapid diffusion. This study examines how diffusion and chemical reactions in the microenvironment of a phytoplankton cell influence the efficiency of both strategies to increase the bioavailability of iron and to reduce iron stress. A numerical model of the cell surroundings is presented that calculates the concentration distribution for different iron species and allows to study the effect of siderophores or surface reductases. It calculates the efficiency of these mechanisms, defined as the quotient between the increase in iron uptake rate and the excretion rate of siderophores or electrons, needed to obtain this increase. The dependence of this efficiency on rates of iron coordination reactions, on diffusivity, and on the kinetics of iron uptake is discussed with the aid of some analytical calculations.