Tab. 3: Differentiation of eroded material in the Arctic Russian Seas

Volumes of Holocene (10 000 years) terrigenous sediments and annnal sediment supply in the Laptev Sea were evaluated from average thickness of the Holocene veneer. Volumes of deposits supplied from various sediment sourees and by different proeesses (abrasion of hinterland and island shores, river discharge, eolian input, drifting ice) were diseriminating of deposition in the eoastal zone, at river/sea barrier, and in the shelf basin itself. Accumulation by drifting iee and the role of local sea bottom erosion were also considered. Total amount of sediments transported from the Laptev Sea shelf to Amundsen and Nansen Basins of the Aretie Ocean was compared with other Russian Aretie seas.

Geochemistry of basalts from ODP Leg 49, North Atlantic Ocean

The geochemistry of basalts recovered from seven sites in the North Atlantic is described with particular reference to minor elements. Three sites (407, 408, and 409) along the same mantle flow line, transverse to the Reykjanes Ridge at about 63°N, provide information on the composition of basalts erupted over a 34-m.y. interval between 2.3 and 36 m.y. ago. At Site 410, at 45°N, penetration into 10 m.y.-old crust west of the ridge axis permits comparisons with young basalts dredged from the median valley at 45°N. Three sites in the FAMOUS area at about 36°N provided material from very young (1 m.y.) basaltic crust (Site 411), and material to test the geochemical coherence of basalts of different ages (1.5 and 3.5 m.y.) on either side of a fracture zone (Sites 412 and 413). These sites complement earlier data from dredged and drilled sites (Leg 37) in the FAMOUS area. At Site 407, four geochemically distinct basalt units occur, with different normative and rare-earth element (REE) characteristics, and there is a clear correlation with magnetic stratigraphy. Yet there is a remarkable consistency in incompatible element ratios between these units, indicating derivation from an essentially similar mantle source. The basalts from the younger sites, 408 and 409, show a similar range of normative and REE variation, but incompatible element ratios are identical to those at Site 407, indicating that basalts at all three sites were produced from a mantle source which was geochemically relatively uniform. Rare-earth differences between the basalts can be interpreted in terms of variations in the degree and depth of partial melting causing HREE (+Y) retention in the source, although there may be some inter-site differences with respect to REE. A similar picture is presented at 45°N. Apparently a range of tholeiitic, transitional, and alkalic basalts were being erupted 10 m.y. ago, which have almost identical geochemical characteristics to those recently erupted in the median valley at 45°N. Incompatible element ratios are markedly different from those recorded at the Reykjanes Ridge. Basalts recovered from the FAMOUS sites are geochemically similar to previous samples recovered from the FAMOUS area, and their incompatible element ratios are similar, but not identical, to those at 45°N. However, total trace element levels are consistently lower than in 45°N basalts, which might imply smaller degrees of partial melting and/or greater depths of magma generation at 45°N, or higher trace element levels in the mantle source at 45°N. Few of the basalts recovered on Leg 49 have the geochemical characteristics of typical "MORB" (e.g., Nazca Plate, Leg 34). The data strongly support models invoking geochemical inhomogeneity in the source regions of basalts produced at the Mid-Atlantic Ridge. However, the data also introduce an additional time factor into such models and demonstrate the uniformity of the mantle source at a particular ridge sector (over periods in excess of 30 m.y.), while emphasizing the marked differences along the ridge. Mixing models invoking "depleted" and "enriched" mantle sources would seem to be inadequate to account for the observed variations.

Sedimentology at the continental margin of the southern Weddell Sea

During four expeditions with RV "Polarstern" at the continental margin of the southern Weddell Sea, profiling and geological sampling were carried out. A detailed bathymetric map was constructed from echo-sounding data. Sub-bottom profiles, classified into nine echotypes, have been mapped and interpreted. Sedimentological analyses were carried out on 32 undisturbed box grab surface samples, as well as on sediment cores from 9 sites. Apart from the description of the sediments and the investigation of sedimentary structures on X-radiographs the following characteristics were determined: grain-size distributions; carbonate and Corg content; component distibutions in different grain-size fractions; stable oxygen and carbon isotopes in planktic and, partly, in benthic foraminifers; and physical properties. The stratigraphy is based On 14C-dating, oxygen isotope Stages and, at one site, On paleomagnetic measurements and 230Th-analyses The sediments represent the period of deposition from the last glacial maximum until recent time. They are composed predominantly of terrigenous components. The formation of the sediments was controlled by glaciological, hydrographical and gravitational processes. Variations in the sea-ice coverage influenced biogenic production. The ice sheet and icebergs were important media for sediment transport; their grounding caused compaction and erosion of glacial marine sediments on the outer continental shelf. The circulation and the physical and chemical properties of the water masses controlled the transport of fine-grained material, biogenic production and its preservation. Gravitational transport processes were the inain mode of sediment movements on the continental slope. The continental ice sheet advanced to the shelf edge and grounded On the sea-floor, presumably later than 31,000 y.B.P. This ice movement was linked with erosion of shelf sediments and a very high sediment supply to the upper continental slope from the adiacent southern shelf. The erosional surface On the shelf is documented in the sub-bottom profiles as a regular, acoustically hard reflector. Dense sea-ice coverage above the lower and middle continental slope resulted in the almost total breakdown of biogenic production. Immediately in front of the ice sheet, above the upper continental slope, a <50 km broad coastal polynya existed at least periodically. Biogenic production was much higher in this polynya than elsewhere. Intense sea-ice formation in the polynya probably led to the development of a high salinity and, consequently, dense water mass, which flowed as a stream near bottom across the continental slope into the deep sea, possibly contributing to bottom water formation. The current velocities of this water mass presumably had seasonal variations. The near-bottom flow of the dense water mass, in combination with the gravity transport processes that arose from the high rates of sediment accumulation, probably led to erosion that progressed laterally from east to West along a SW to NE-trending, 200 to 400 m high morphological step at the continental slope. During the period 14,000 to 13,000 y.B.P., during the postglacial temperature and sea-level rise, intense changes in the environmental conditions occured. Primarily, the ice masses on the outer continental shelf started to float. Intense calving processes resulted in a rapid retreat of the ice edge to the south. A consequence of this retreat was, that the source area of the ice-rafted debris changed from the adjacent southern shelf to the eastern Weddell Sea. As the ice retreated, the gravitational transport processes On the continental slope ceased. Soon after the beginning of the ice retreat, the sea-ice coverage in the whole research area decreased. Simultaneously, the formation of the high salinity dense bottom water ceased, and the sediment composition at the continental slope then became influenced by the water masses of the Weddell Gyre. The formation of very cold Ice Shelf Water (ISW) started beneath the southward retreating Filchner-Ronne Ice Shelf somewhat later than 12,000 y.B.P. The ISW streamed primarily with lower velocities than those of today across the continental slope, and was conducted along the erosional step on the slope into the deep sea. At 7,500 y.B.P., the grounding line of the ice masses had retreated > 400 km to the south. A progressive retreat by additional 200 to 300 km probably led to the development of an Open water column beneath the ice south of Berkner Island at about 4,000 y.B.P. This in turn may have led to an additional ISW, which had formed beneath the Ronne Ice Shelf, to flow towards the Filcher Ice Shelf. As a result, increased flow of ISW took place over the continental margin, possibly enabling the ISW to spill over the erosional step On the upper continental slope towards the West. Since that time, there is no longer any documentation of the ISW in the sedimentary Parameters on the lower continental slope. There, recent sediments reflect the lower water masses of the Weddell Gyre. The sea-ice coverage in early Holocene time was again so dense that biogenic production was significantly restricted.

Magnesium concentrations of individual shells of Globorotalia truncatulinoides

Recent work has provided useful Mg/Ca to water temperature calibrations for shallow-dwelling planktonic foraminifer species. Globorotalia truncatulinoides (right coiling (R)) is a deep-dwelling species that can serve as a source of information about the temporal variability in the water characteristics of the thermocline. We present a temperature calibration for the Mg/Ca in the shell of G. truncatulinoides (R) and examine some of the practical issues associated with evaluating the usefulness of the technique. The Mg/Ca in the primary and the secondary calcite of individual G. truncatulinoides (R) correlates exponentially with water column temperatures, showing a change of ~10% in the Mg/Ca per 1°C (R**2 = 0.92). A limited comparison with plankton tow samples demonstrates that the average Mg/Ca temperature was offset +1°C from the average temperature calculated using the d18O calibration of O'Neil et al. (1969, doi:10.1063/1.1671982), and the Mg/Ca temperatures have a range similar to the ?18O temperatures. Comparisons of the [Mg] in the core top samples to water depth of deposition indicates that dissolution does not alter the measured value of Mg in the primary calcite.

Chemical composition and solubility of ocean phosphatized rocks in seawater

In order to elucidate possibility of limestone phosphatization during contact with seawater two sets of experiments were carried out: that of solubility of natural phosphates in seawater and that of deposition of phosphorus onto calcareous phase. Concentration of phosphorus in seawater used for solubility experiments varied from 39 to 338 µ/l, temperature was 5.5-17.5°C and pH 7.8-7.9. The lowest solubility was characteristic of ancient crystallized samples. The deposition experiments showed that in case when concentration of dissolved phosphate in seawater reaches 3 mg/l it might be sorbed on solid CaCO3 phase without forming its own mineral. The latter is able to form rapidly but only if magnesium is not present in solution. In magnesium-free water calcium phosphates precipitate when concentration of dissolved phosphorus is higher than 0.9-1.2 mg/l. These results show that phosphatization of limestones in marine environment takes place during their contact with pore water but not with marine bottom water.

Eocene benthic foraminifera of DSDP Hole 93-605

This paper describes and illustrates early to middle Eocene benthic foraminifers from northwest Atlantic Site 605, on the continental rise off New Jersey. Benthic foraminiferal faunas are dominated by Bulitnina spp., Nuttallides truempyi, Lenticulina spp., and Cibicidoides spp. Other common taxa include Oridorsalis spp., Gyroidinoides spp., uniserial taxa, arenaceous taxa, and Globocassidulina subglobosa. Together, these taxa usually make up 70% or more of the total fauna. The assemblages are interpreted as indicating a lower bathyal environment of deposition during the Eocene at Site 605. This is corroborated by an independent water depth estimate through backstripping, indicating a water depth for the beginning of the Eocene to late middle Eocene of approximately 2300 to 2000 m.

Description of recent sediments of Nile Delta, Red Sea and Gulf of Aden (Table 1-3)

The study of textural, structural, chemical, and physical properties of fine-grained recent marine sediments leads to the conclusion that only a few compositional factors are responsible for significant changes in mass physical characteristics in the upper meters below sea bottom. Fossil-induced porosity increases water content and liquid limit. It also seems to have partially influenced the plastic limit and plasticity index of calcareous sandy silts from the Red Sea and the western Gulf of Aden so that they become similar to the montmorillonite rich prodelta clays from the Nile Delta. Diagrams based on liquid limit and plasticity loose their original meaning in these cases. Activity of sediments rich in microorganisms can be higher than that of montmorillonitic clay. The shear strength-depth relationship of normally consolidated sediments is surprisingly little influenced by changes in sand or clay content and clay mineralogy. Only high lime content, submarine erosion and beginning cementation increase the strength considerably. Erosional disconformities near the present surface can be deduced from the strength-depth curve when as little as 1 or 2 m sediment have been removed. Flat or irregular strength-depth curves indicate beginning cementation and probably discontinuous sedimentation, provided the composition of the material remains in some degree constant. In our samples diagenetic pyrite, but no recristallisation of carbonates could be detected under the microscope. Underconsolidation and excess pore-water pressure, factors which tend to foster submarine slides, mud lumps, and diapiric folding, seem to be restricted Varito areas with mainly rapidly deposited, homogeneous or layered sediments. But where an abundance of burrowing organisms increases the vertical permeability of the sediment, normal consolidation and stable deposits are to be expected, at least in the upper meters below the present surface. According to 14C-determinations on calcareous microorganisms the rate of deposition of the investigated sediments seems to range from 26 to 167 cm per 1000 years.

Grain size distribution analysis of prominent beds on Southern Central Chilean seamounts

Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru-Chile Trench off Southern Central Chile (36°S-39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175-450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope.

Geochemistry and age models of sediments from the Celtic margin

The sedimentary sections of three cores from the Celtic margin provide high-resolution records of the terrigenous fluxes during the last glacial cycle. A total of 21 14C AMS dates allow us to define age models with a resolution better than 100 yr during critical periods such as Heinrich events 1 and 2. Maximum sedimentary fluxes occurred at the Meriadzek Terrace site during the Last Glacial Maximum (LGM). Detailed X-ray imagery of core MD95-2002 from the Meriadzek Terrace shows no sedimentary structures suggestive of either deposition from high-density turbidity currents or significant erosion. Two paroxysmal terrigenous flux episodes have been identified. The first occurred after the deposition of Heinrich event 2 Canadian ice-rafted debris (IRD) and includes IRD from European sources. We suggest that the second represents an episode of deposition from turbid plumes, which precedes IRD deposition associated with Heinrich event 1. At the end of marine isotopic stage 2 (MIS 2) and the beginning of MIS 1 the highest fluxes are recorded on the Whittard Ridge where they correspond to deposition from turbidity current overflows. Canadian icebergs have rafted debris at the Celtic margin during Heinrich events 1, 2, 4 and 5. The high-resolution records of Heinrich events 1 and 2 show that in both cases the arrival of the Canadian icebergs was preceded by a European ice rafting precursor event, which took place about 1-1.5 kyr before. Two rafting episodes of European IRD also occurred immediately after Heinrich event 2 and just before Heinrich event 1. The terrigenous fluxes recorded in core MD95-2002 during the LGM are the highest reported at hemipelagic sites from the northwestern European margin. The magnitude of the Canadian IRD fluxes at Meriadzek Terrace is similar to those from oceanic sites.

Annotated record of the detailed examination of Mn deposits from the R/V Thomas Washington ROUNDABOUT Cruise stations

The cores described are taken during the R/V Thomas Washington ROUNDABOUT Cruise from May 1988 until March 1989 by the Scripps Institute of Oceanography. A total of 159 cores and dredges were recovered and are available at Scripps Institute of Oceanography for sampling and study.

Stable-isotope ratios and accumulation rates of four firn cores from the Dronning Maud Land, Antarctica

Four firn cores were retrieved in 2007 at two ridges in the area of the Ekström Ice Shelf, Dronning Maud Land, coastal East Antarctica, in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate-depth core. Stable water-isotope analysis, tritium content and electrical conductivity were used to date the cores. For the period 1981-2006 a strong and significant correlation between the stable-isotope composition of firn cores in the hinterland and mean monthly air temperatures at Neumayer station was (r=0.54-0.71). No atmospheric warming or cooling trend is inferred from our stable-isotope data for the period 1962-2006. The stable-isotope record of the ice/firn cores could expand well beyond the meteorological record of the region. No significant temporal variation of accumulation rates was detected. However, decreasing accumulation rates were found from coast to hinterland, as well as from east (Halvfarryggen) to west (Søråsen). The deuterium excess (d) exhibits similar differences (higher d at Søråsen, lower d at Halvfarryggen), with a weak negative temporal trend on Halvfarryggen (0.04 per mil/a), probably implying increasing oceanic input. We conclude that Halvfarryggen acts as a natural barrier for moisture-carrying air masses circulating in the region from east to west.

(Table 1, Page 1046-1047) Chemical composition of iron-manganese concretions from the Indian Ocean recovered by the R/V Vityaz and the R/V Ob

The data given in this and previous communications is insufficient to assess the quantitative role of these supplementary sources in the Indian Ocean, but they do not rule out their local significance. Elucidation of this problem requires further data on the characteristics of the composition and structure of nodules in various different metallogenic regions of the ocean floor. A study of the distribution of ore elements in nodules both depthwise and over the area of the floor together with compilation of the first schematic maps based on the results of analyses of samples from 54 stations) enables us to give a more precise empirical relation between the Mn, Fe, Ni, Cu, and Co contents in Indian Ocean nodules, the manganese ratio and the values of the oxidation potential, which vary regularly with depth. This in turn also enables us to confirm that formation of nodules completes the prolonged process of deposition of ore components from ocean waters, and the complex physico-chemical transformations of sediments in the bottom layer. Microprobe investigation of ore rinds revealed the nonuniform distribution of a num¬ber of elements within them, owing to the capacity of particles of hydrated oxides of manganese and iron to adsorb various elements. High concentration of individual elements is correlated with local sectors of the ore rinds, in which the presence of todorokite, in particular, has been noted. The appearance of this mineral apparently requires elevated Ca, Mg, Na, and K concentrations, because the stable crystalline phase of this specific mineral form of the psilomelane group may be formed when these cations are incorporated into a lattice of the delta-MnO2 type.

X-ray diffraction analysis, binocular component analysis and radiocarbon dating of sediment cores from the NW Iberian shelf system

Based on a well-established stratigraphic framework and 47 AMS-14C dated sediment cores, the distribution of facies types on the NW Iberian margin is analysed in response to the last deglacial sea-level rise, thus providing a case study on the sedimentary evolution of a high-energy, low-accumulation shelf system. Altogether, four main types of sedimentary facies are defined. (1) A gravel-dominated facies occurs mostly as time-transgressive ravinement beds, which initially developed as shoreface and storm deposits in shallow waters on the outer shelf during the last sea-level lowstand; (2) A widespread, time-transgressive mixed siliceous/biogenic-carbonaceous sand facies indicates areas of moderate hydrodynamic regimes, high contribution of reworked shelf material, and fluvial supply to the shelf; (3) A glaucony-containing sand facies in a stationary position on the outer shelf formed mostly during the last-glacial sea-level rise by reworking of older deposits as well as authigenic mineral formation; and (4) A mud facies is mostly restricted to confined Holocene fine-grained depocentres, which are located in mid-shelf position. The observed spatial and temporal distribution of these facies types on the high-energy, low-accumulation NW Iberian shelf was essentially controlled by the local interplay of sediment supply, shelf morphology, and strength of the hydrodynamic system. These patterns are in contrast to high-accumulation systems where extensive sediment supply is the dominant factor on the facies distribution. This study emphasises the importance of large-scale erosion and material recycling on the sedimentary buildup during the deglacial drowning of the shelf. The presence of a homogenous and up to 15-m thick transgressive cover above a lag horizon contradicts the common assumption of sparse and laterally confined sediment accumulation on high-energy shelf systems during deglacial sea-level rise. In contrast to this extensive sand cover, laterally very confined and maximal 4-m thin mud depocentres developed during the Holocene sea-level highstand. This restricted formation of fine-grained depocentres was related to the combination of: (1) frequently occurring high-energy hydrodynamic conditions; (2) low overall terrigenous input by the adjacent rivers; and (3) the large distance of the Galicia Mud Belt to its main sediment supplier.

(Table, page 351-359) Chemical composition of manganese nodules and crusts from the Pacific and Indian Ocean

Chemical and mineralogical analyses of manganese nodules from a large number of widely spaced localities in the Pacific and Indian Oceans have shown that their mineralogy and chemical composition varies both areally and with depth of formation. This is considered to result from a number of factors, important among which are: (a) their proximity to continental or volcanic sources of elements; (b) the chemical environment of deposition, including the degree of oxygenation; and (c) local factors such as the upward migration of reduced manganese in sediments from certain areas. Sub-surface nodules appear to share the chemical characteristics of their surface counterparts, especially those from volcanic areas where sub-surface sources of elements are probably important.

(Table 1) Peak intensities and stable carbon and oxygen isotope ratios of various diagenetic carbonates of ODP Site 128-799

Abundant and various diagenetic carbonates were recovered from a 1084-m-thick, Quaternary to lower Miocene section at ODP Site 799 in the Japan Sea. Petrographic, XRD, SEM, EDS-chemical, and isotopic analyses revealed wide variations in occurrence and textural relations and complex mineralogy and chemistry. Diagenetic carbonates include calcite, calcium-rich rhodochrosite, iron- and manganese-rich magnesite, iron- and manganese-rich dolomite and ankerite, and iron- and manganeserich lansfordite (hydrous Mg-carbonate). Rhodochrosite commonly occurs as small, solid nodules and semi-indurated, thin layers in bioturbated, mottled sediments of Units I and II (late Miocene to Quaternary). Lansfordite occurs as unindurated nodules and layers in Unit II (late Miocene and Pliocene), whereas magnesite forms indurated beds a few centimeters thick in slightly bioturbated-to-faintly laminated sediments of Unit III (middle and late Miocene). Some rhodochrosite nodules have dark-colored, pyritic cores, and some pyrite-rhodochrosite nodules are overgrown by and included within magnesite beds. Dolomite and ankerite tend to form thick beds (>10 cm) in bedded to laminated sediments of Units III, IV, and V (early to late Miocene). Calcite occurs sporadically throughout the Site 799 sediments. The d18O values of carbonates and the interstitial waters, and the measured geothermal gradient indicate that almost all of the Site 799 carbonates are not in isotopic equilibrium with the ambient waters, but were precipitated in the past when the sediments were at shallower depths. Depths of precipitation obtained from the d18O of carbonates span from 310 to 510 mbsf for magnesite and from 60 to 580 mbsf for dolomite-ankerite. Rhodochrosite and calcite are estimated to have formed within sediments at depths shallower than 80 mbsf. Diagenetic history in the Site 799 sediments have been determined primarily by the environment of deposition; in particular, by the oxidation-reduction state of the bottom waters and the alkalinity level of the interstitial waters. Under the well-oxygenated bottom-water conditions in the late Miocene and Pliocene, manganese initially accumulated on the seafloor as hydrogenous oxides and subsequently was mobilized and reprecipitated as rhodochrosite within the shallow sulfate-reduction, sub-oxic zone. Precipitation of lansfordite occurred in the near-surface sediments with abundant organic carbon and an extremely high alkalinity during the latest Miocene and Pliocene. The lansfordite was transformed to magnesite upon burial in the depth interval 310 to 510 mbsf. Dolomite first precipitated at shallow depths in Mn-poor, anoxic, moderately biocalcareous sediments of early to late Miocene. With increasing temperature and depth, the dolomite recrystallized and reequilibrated with ambient waters at depths below about 400 mbsf.