Holocene sediment transport from the glaciated margin of East/Northeast Greenland to the N Iceland shelves

We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the fraction of "far-travelled" sediments in the Denmark Strait environs is overwhelmingly of local, mid-East Greenland, provenance, and therefore with a significant cross-channel component to their travel. The Holocene record of ice-rafted sediments denotes a three-part division of the Holocene in terms of iceberg sediment transport with a notable increase in the process starting ca 4000 cal yr BP. This latter increase may represent the re-advance during the Neoglacial period of land-terminating glaciers on the Geikie Plateau to become marine-terminating. The contrast in spectral signals between these cores and the 1500-yr cycle at VM28-14, just south of the Denmark Strait, combined with the coupled iceberg-model results, leads us to speculate that the signal at VM28-14 reflects pulses in overflow waters, rather than an ice-rafted signal.

Abundance of nodules, chemical and mineral compositions of nodules and sediments from the Central Pacific

The monograph considers facial conditions of ore-formation in the Central Equatorial Pacific, as well as lithostratigraphy and local variability of bottom sediments. Mineral composition of nodules, forms of occurrence of chemical elements in sediments and nodules, composition of interstitial waters, age of nodules, regularities and processes of ore formation in the radiolarian belt of the Pacific Ocean zone are also under consideration.

Vertical variations in basic salt composition of interstitial waters from Pacific sediments

Basic chemical composition of interstitial water in sediments of the Northwestern Pacific along a profile from the continental shelf of the Japan Trench to the ocean bed is discussed. Transformation of interstitial water in sediments rich in organic matter on the continental shelf and at the bottom of the Japan Trench is indicated. Variation in the vertical direction of elementary constituents of interstitial salt solution and variations in certain biogenic elements permit to make conclusions concerning processes taking place in sediments during sedimentation and diagenesis. These processes cause both metamorphism of water and transformation of organic and mineral content of sediments.

Chemical composition of sediments and interstitial waters in the Gulf of California and Eastern Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Chemistry of interstitial waters of ODP Leg 112 samples

Two distinct hydrogeochemical regimes currently dominate the Peruvian continental margin. One, in shallower water (150-450 m) shelf to upper-slope regions, is characterized by interstitial waters with strong positive chloride gradients with depth. The maximum measured value of 1043 mM chloride at Site 680 at ITS corresponds to a degree of seawater evaporation of ~2 times. Major ion chemistry and strontioum isotopic composition of the interstitial waters suggest that a subsurface brine that has a marine origin and is of pre-early Miocene "age," profoundly influences the chemistry and diagenesis of this shelf environment. Site 684 at ~9°S must be closest to the source of this brine, which becomes diluted with seawater and/or interstitial water as it flows southward toward Site 686 at ~13?S (and probably beyond) at a rate of approximately 3 to 4 cm/yr, since early Miocene time. The other regime, in deep water (3000-5000 m) middle to lower-slope regions, is characterized by interstitial waters with steep negative and nonsteady-state chloride gradients with depth. The minimum measured value of 454 mM chloride, at Site 683 at ITS, corresponds to ~20% dilution of seawater chloride The most probably sources of these low-chloride fluids are gas hydrate dissociation and mineral (particularly clay) dehydration reactions. Fluid advection is consistent with (1) the extent of dilution shown in the chloride profiles, (2) the striking nonsteady-state depth profiles of chlorides at Sites 683 and 688 and of 87Sr/86Sr ratios at Site 685, and (3) the temperatures resulting from an average geothermal gradient of 50°C/km and required for clay mineral dehydration reactions. Strontium isotope data reveal two separate fluid regimes in this slope region: a more northerly one at Sites 683 and 685 that is influenced by fluids with a radiogenic continental strontium signature, and a southerly one at Sites 682 and 688 that is influenced by fluids with a nonradiogenic oceanic signatures. Stratigraphically controlled fluid migration seems to prevail in this margin. Because of its special tectonic setting, Site 679 at ITS is geochemically distinct. The interstitial waters are characterized by seawater chloride concentrations to -200 mbsf and deeper by a significantly lower chloride concentration of about two-thirds of the value in seawater, suggesting mixing with a meteoric water source. Regardless of the hydrogeochemical regime, the chemistry and isotopic compositions of the interstitial waters at all sites are markedly modified by diagenesis, particularly by calcite and dolomite crystallization.

Chemical composition of upper Cenozoic at DSDP Leg 70 Holes

The hydrothermal deposits that we analyzed from Leg 70 are composed of ferruginous green clays and fragments of manganese-hydroxide crust. Data from X-ray diffraction, IR-spectroscopy, electron diffraction, and chemical analyses indicate that the hydrothermal green clays are composed of disordered mixed-layer phases of celadonite-nontronite. Electron diffraction shows that the parameters of the unit cells and the degree of three-dimensional ordering of mixed-layer phases with 80% celadonite interlayers are very close to Fe-micas of polymorphic modification IM-celadonite. In some sections, there is a tendency for the number of celadonite layers to increase with depth. The manganese-hydroxide crust fragments are predominantly composed of todorokite (buserite). An essential feature of hydrothermal accumulation is the sharp separation of Fe and Mn. Ba/Ti and Ba/Sr ratios are typical indicators of hydrothermal deposits. Sediments composing the hydrothermal mounds were deposited from moderately heated waters, which had extracted the components from solid basalts in environments where there were considerable gradients of temperature, eH, and pH. The main masses of Fe and Mn were deposited in the late Pleistocene. Postsedimentary alteration of deposited hydrothermal sediments led to their slight recrystallization and, in the green clays, to celadonitization. Further, factor analysis (by Varentsov) of chemical components from these hydrothermal deposits revealed paragenetic assemblages. Green clays corresponding to a definite factor assemblage were formed during the main stage of hydrothermal mineral formation. Manganese hydroxide and associated components were largely accumulated during an early stage and at the end of the main stage.

Sulfur in bottom sediments and intersitial waters of the Gulf of California

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Sedimentology, mineral magnetism, andoxygen isotope stratigraphy of ODP Hole 133-819A

To investigate late Quaternary paleoclimatic and paleoceanographic change in the sedimentary record, preserved on the Australian Continental Margin during the late Quaternary, core material was collected from Ocean Drilling Program, Leg 133, Site 819. An expanded sequence of late Quaternary, rhythmically bedded, predominantly hemipelagic sediments were recovered from Hole 819A. The foraminiferal d18O record preserved at Hole 819A suggests that the late Quaternary section is incomplete. Both benthic and planktonic d18O stratigraphies can be traced tentatively downcore to stage 6 at about 32.5 mbsf, where a major hiatus occurs. At this level, a slump detachment surface has been identified (Shipboard Scientific Party, 1991). This slump has removed marine oxygen isotope stages 7 to 13. Below 32.5 mbsf, continuous correlation can be achieved in the planktonic d18O curve, with existing deep-sea foraminiferal oxygen isotope stratigraphies from stage 14 through stage 28. The major hiatus at 32.5 mbsf marks the position of a significant change in the character of the sedimentation at Site 819. Sediments below 32.5 mbsf, relative to those above 32.5 mbsf, are characterized by less variation in mean particle size; lower percentages of carbonate content in the coarse fraction (>63 µm); a stronger relationship between the percentage of fine fraction and magnetic mineral concentration, and lower foraminiferal abundances. Above the hiatus, large fluctuations in mean particle size occurred, which have been interpreted to be the result of high foraminiferal abundances. Early highstands show high terrigenous influx in the fine fraction above the hiatus. This is the opposite of the general idea of high terrigenous influx during lowstands of sea level on siliciclastic dominated continental margins. We are far from understanding the origin of this material and further investigation will be required (see also Glenn et al., this volume). All our records, except the planktonic foraminiferal oxygen isotope record, indicate that the major hiatus marks the position of a significant change in the environment at Site 819. The planktonic foraminiferal d18O record suggests that environmental change occurred prior to the formation of the hiatus (i.e., near the Brunhes/Matuyama [B/M] boundary). The interval between the B/M boundary and the hiatus represents a transitional period between two different patterns of ocean circulation. Throughout most of the lower part of the sequence, Site 819 was at a shallow-water depth and local oceanographic conditions were dominated by sluggish Subtropical Central Water (SCW) flow. However, near the B/M boundary, ocean circulation patterns intensified, reflecting a worldwide change in paleoenvironment. Enhanced ocean circulation patterns were possibly aided by tectonic subsidence. During this period Site 819 became progressively more under the influence of Antarctic Intermediate Water (AAIW), than SCW. In the upper part of the sequence at Hole 819 A, we see a continuation of the pattern of oceanographic reorganization suggested during stages 21 through 14. Intensification of the subsurface oceanographic circulation was also accompanied by the progressive wedging southward of surface waters associated with the East Australian Current (EAC). The change in the nature of the records in the lower and upper parts of the sequence at Site 819 are thought to reflect perturbations by the orbital eccentricity cycle.

Concentrations of phosphates and silicon in near-bottom and interstitial waters of the Baltic Sea

Fine structure of vertical distributions of phosphorus and silicon in near-bottom layers and interstitial waters is studied in different regions of the Baltic Sea (Gulf of Finland, Bornholm area, Gotland trench). Data obtained are used to calculate fluxes of mineral forms of phosphorus and silicon in exchange processes between sediments and the near-bottom water layer. Depending on sediment types, values of nutrient fluxes vary from 9.8 to 632.6 µg-at/m**2/day for phosphorus and from 232.4 to 1881.1 µg-at/m**2/day for silicon. Fluxes calculated for different regions are compared.

Sulfur compounds in bottom sediments and interstitial waters of the Pacific Ocean to the east of Japan

In near-shore Pacific bottom sediments to the east of Japan unusually high content of free H2S ocurs. H2S resulting from bacterial reduction of sulfates from interstitial waters has a number of derivatives; pyrite dominates among them. Contents of other derivatives of H2S: sulfide sulfur and organic sulfur do not exceed 0,01%, content of organic sulfur does not exceed 0.1%. Due to reduction content of sulfates can reduce to 0,03% S. Capacity of the process of sulfate reduction, estimated by sum of all reduced forms of S - derivatives of H2S, is a function of organic matter content in sediments. Ability of bottom sediments to accumulate free H2S depends on content of reactive forms of Fe. Spatial distribution of reduced forms of S in the studied sediments is considered.

Composition of interstitial waters from sediments of the Gulf of California

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.