Oxygen isotopes from two snow trenches from Kohnen Station, Dronning Maud Land, Antarctica from the 2012/13 field season

In low-accumulation regions, the reliability of d18O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen station, Dronning Maud Land, Antarctica. Analysing d18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the hundred-metre scale. This data set includes the complete trench oxygen isotope record together with the meta data used in the study.

DEP-derived density from two snow trenches from Kohnen Station, Dronning Maud Land, Antarctica from the 2012/13 field season

The density of firn is an important property for monitoring and modeling the ice sheet as well as to model the pore close-off and thus to interpret ice core-based greenhouse gas records. One feature, which is still in debate, is the potential existence of an annual cycle of firn density in low-accumulation regions. Several studies describe or assume seasonally successive density layers, horizontally evenly distributed, as seen in radar data. On the other hand, high-resolution density measurements on firn cores in Antarctica and Greenland showed no clear seasonal cycle in the top few meters. A major caveat of most existing snow-pit and firn-core based studies is that they represent one vertical profile from a laterally heterogeneous density field. To overcome this, we created an extensive dataset of horizontal and vertical density data at Kohnen Station, Dronning Maud Land on the East Antarctic Plateau. We drilled and analyzed three 90 m long firn cores as well as 160 one meter long vertical profiles from two elongated snow trenches to obtain a two dimensional view of the density variations. The analysis of the 45 m wide and 1 m deep density fields reveals a seasonal cycle in density. However, the seasonality is overprinted by strong stratigraphic noise, making it invisible when analyzing single firn cores. Our density dataset extends the view from the local ice-core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores.

The hydrographic conditions at depth below 1000 m water depth in the region of the Romanche Fracture Zones

During the "Atlantic Expedition" in1965 (IQSY) a comprehensive bathymetric survey and a few hydrographic stations were made by R.V. "Meteor" in the equatorial region of the Mid-Atlantic Ridge. The survey results are shown in a bythymetric chart covering the western parts of the Romanche- and Chain Fracture Zones. West of the original Romanche Trench another deep trench with a medium depth of 6000 m was discovered. The maximum sounding obtained was 7028 m. Both trenches apparently belong to the same fracture zone, but are distinctly separated from each other. The estern boundary of the trench against the Brasil Basin is formed by a sill rising to a depth of about 4400 m. The serial hydrographic observations give some indications of the flow of the cold Westatlantic deep water in the fracture zone area and its influence on the hydrographic conditions in the East-Atlantic Basin. The upper limit of the nearly homogenious Westatlantic bottom water with an Antarctic components lies about 4400 m. The water mass entering the system of trenches of the Romanche Fracture Zone over the western sill originates from the lower part of the discontinuity layer lying above the bottom water. Potential temperatures of 0.6°C were the lowest observed by "Meteor" in the western trench. There seems to be a remarkable tongue of relatively high salinity and a minimum of oxygen in the deep water of this trench. At present we can only speculate upon the origin of this highly saline deep water tongue underneath the eastward moving relatively thin layer of less saline Westatlantic deep water. In the range of the sill separating both trenches a lee wave is indicated by the distribution of salinity and oxygen, which implies a vertical transport of water masses. Caused by this transport it is assumed that relatively cold water may be lifted temporarily to a depth, where it can pass the northbounding ridge, thus getting directly into the Sierra Leone Basin. In the original Romanche Trench the cold Westatlantic deep water seems to fill the whole trough, but its extension remains limited to the trench itself. The water masses found east of the sill separating the trench from the East-Atlantic Basin originate from the lower part of the discontinuity layer. With potential temperatures of about 1.3°C they are much warmer than those observed in the Romanche Trench bottom water.

Geochemistry at DSDP Hole 57-439

Dating of a hornblende concentrate by the 40Ar/39Ar method gives an age of 23.4±5.5 m.y. for a dacite boulder from conglomerate in Deep Sea Drilling Project Hole 439. The conglomerate clasts range up to 1 meter in diameter and are nearly monolithologic, suggesting that a nearby former volcano erupted the dacite. The dacite is only 90 km landward from the Japan Trench, whereas modern trench-related volcanoes lie at least 120 km from their trenches. The dacite locality is on strike with and is probably an extension of a magmatic arc on the island of Hokkaido that crosses the Kuril arc at an angle of 65° and which was active 16 to 36 m.y. ago. The part of the former arc landward from the Kuril arc argues against an origin from a leaking subduction zone or from subduction of an active spreading ridge. The part seaward both from the Kuril and Japan arcs weakens an explanation based on migration of a trench-trenchtrench triple junction. The magmatic rocks probably formed along a middle-Tertiary plate boundary that had stepped seaward from a more-landward Cretaceous position. Later, the boundary stepped farther seaward at the Kuril arc and landward again at the Japan arc. If so, the present Japan subduction zone must have consumed most of the strata that had accumulated between it and the earlier trench.

Interstitial water and sediment chemistry at DSDP Sites 87-582 and 87-584

Two trenches off Japan were explored during DSDP Leg 87. One is the Nankai Trough and the other is the Japan Trench; Site 582 is located on the floor of the former and Site 584 is situated on the deep-sea terrace of the latter. Cores from Site 582 and 584 consist mainly of hemipelagic sediments and diatomaceous silts and mudstone, respectively. In this report we analyze the chemistry of the interstitial water and sediments, as well as the sediment mineralogy. Sulfate reduction is accompanied by the production of secondary pyrite, which is rich in the sediment at both sites. Dissolved Ca concentration is relatively low and changes only slightly at both sites, probably because of the formation of carbonate with high alkalinity. Concentrations of dissolved Mg decrease with depth at Site 584. The dissolved Mg depletion probably results from the formation of Mg-rich carbonate and/or ion exchange and reaction between interstitial water and clay minerals. Higher Si/Al values are due to biogenic opal in the sediments and roughly correlate with higher values of interstitial water SiO2. Increases in dissolved Li concentrations may be related to its release from clay minerals, to advection that results from dewatering, and/or to fluid transport.

Selected Devonian/Carboniferous boundary profiles in the Sauerland area (Rhenish massif)

Selected sections, containing Devonian/Carboniferous boundary beds, are described from the northern and northeastern margin of the Rhenish massif, especially from the Seiler region near Iserlohn and the Warstein area. These sections are from prospecting trenches, quarries and road cuts. The dominantly carbonate sequences were investigated in regard to the development of conodonts. The Devonian/Carboniferous boundary could be placed precisely in both areas by means of the phylogenetic transition from Siphonodella praesulcata to S. sulcata. Compared investigations lead to the following conclusions: - The basal part of the Hangenberg limestone is heterochronous. - The Devonian/Carboniferous boundary lies distinctly below the Hangenberg limestone, i. e. at the same stratigraphical level as the Stockum limestone. - The Imitoceras limestone lens of Stockum and the Stockum limestone represent a special facies within the Hangenberg schists. 80th belong either to the praesulcata- and sulcata-zone or are restricted only to the sulcata-zone. - Protognathodus kuehni appears together with Siphonodella sulcata. Where S. sulcata is lacking, P. kuehni may be considered as a valid index conodont indicating the beginning of the Carboniferous. - The upper part of the Wocklum beds, following above the Wocklum limestone, usually consists up to the lower Carbonilerous boundary in a more or less consistent facies, that of the Hangenberg schists. Only in the section 01 the northeastern wall of the eastern Provincial Quarry at Drewer and in the road profile Rüthen - Nuttlar, the Devonian/Carboniferous boundary is to be placed in a continuous carbonate sequence. - The eastern Provincial Quarry at Drewer is therefore proposed as a new candidate section for the Devonian/Carboniferous boundary stratotype. - In many places the carbonates at the Devonian / Carboniferous boundary and the Hangenberg limestone are characterized by an impoverished conodont fauna. - Using platform conodonts, biofacies models are developed, permitting to conclude on the position of the respective setting 01 sedimentation area, either close to a rise or a basin.

Chemical composition of bottom sediments at DSDP Sites 91-595 and 91-596 and ODP Sites 114-701 and 129-801

Subducted sediments play an important role in arc magmatism and crust-mantle recycling. Models of continental growth, continental composition, convergent margin magmatism and mantle heterogeneity all require a better understanding of the mass and chemical fluxes associated with subducting sediments. We have evaluated subducting sediments on a global basis in order to better define their chemical systematics and to determine both regional and global average compositions. We then use these compositions to assess the importance of sediments to arc volcanism and crust-mantle recycling, and to re-evaluate the chemical composition of the continental crust. The large variations in the chemical composition of marine sediments are for the most part linked to the main lithological constituents. The alkali elements (K, Rb and Cs) and high field strength elements (Ti, Nb, Hf, Zr) are closely linked to the detrital phase in marine sediments; Th is largely detrital but may be enriched in the hydrogenous Fe-Mn component of sediments; REE patterns are largely continental, but abundances are closely linked to fish debris phosphate; U is mostly detrital, but also dependent on the supply and burial rate of organic matter; Ba is linked to both biogenic barite and hydrothermal components; Sr is linked to carbonate phases. Thus, the important geochemical tracers follow the lithology of the sediments. Sediment lithologies are controlled in turn by a small number of factors: proximity of detrital sources (volcanic and continental); biological productivity and preservation of carbonate and opal; and sedimentation rate. Because of the link with lithology and the wealth of lithological data routinely collected for ODP and DSDP drill cores, bulk geochemical averages can be calculated to better than 30% for most elements from fewer than ten chemical analyses for a typical drill core (100-1000 m). Combining the geochemical systematics with convergence rate and other parameters permits calculation of regional compositional fluxes for subducting sediment. These regional fluxes can be compared to the compositions of arc volcanics to asses the importance of sediment subduction to arc volcanism. For the 70% of the trenches worldwide where estimates can be made, the regional fluxes also provide the basis for a global subducting sediment (GLOSS) composition and flux. GLOSS is dominated by terrigenous material (76 wt% terrigenous, 7 wt% calcium carbonate, 10 wt% opal, 7 wt% mineral-bound H2O+), and therefore similar to upper continental crust (UCC) in composition. Exceptions include enrichment in Ba, Mn and the middle and heavy REE, and depletions in detrital elements diluted by biogenic material (alkalis, Th, Zr, Hf). Sr and Pb are identical in GLOSS and UCC as a result of a balance between dilution and enrichment by marine phases. GLOSS and the systematics of marine sediments provide an independent approach to the composition of the upper continental crust for detrital elements. Significant discrepancies of up to a factor of two exist between the marine sediment data and current upper crustal estimates for Cs, Nb, Ta and Ti. Suggested revisions to UCC include Cs (7.3 ppm), Nb (13.7 ppm), Ta (0.96 ppm) and TiO2 (0.76 wt%). These revisions affect recent bulk continental crust estimates for La/Nb and U/Nb, and lead to an even greater contrast between the continents and mantle for these important trace element ratios. GLOSS and the regional sediment data also provide new insights into the mantle sources of oceanic basalts. The classical geochemical distinction between 'pelagic' and 'terrigenous' sediment sources is not valid and needs to be replaced by a more comprehensive understanding of the compositional variations in complete sedimentary columns. In addition, isotopic arguments based on surface sediments alone can lead to erroneous conclusions. Specifically, the Nd/Hf ratio of GLOSS relaxes considerably the severe constraints on the amount of sediment recycling into the mantle based on earlier estimates from surface sediment compositions.

Geochemistry of ODP Site 123-765 sediments

Drilling at Site 765 in the Argo Abyssal Plain sampled sediments and oceanic crust adjacent to the Australian margin. Some day, this site will be consumed in the Java Trench. An intensive analytical program was conducted to establish this site as a geochemical reference section forcrustal recycling calculations. About 150 sediment samples from Site 765 were analyzed for major and trace elements. Downhole trends in the sediment analyses agree well with trends in sediment mineralogy, as well as in Al and K logs. The primary signal in the geochemical variability is dilution of a detrital component by both biogenic silica and calcium carbonate. Although significant variations in the nonbiogenic component occur through time, its overall character is similar to nearby Canning Basin shales, which are typical of average post-Archean Australian shales (PAAS). The bulk composition of the hole is calculated using core descriptions to weight the analyses appropriately. However, a remarkably accurate estimate of the bulk composition of the hole can be made simply from PAAS and the average calcium carbonate and aluminum contents of the hole. Most elements can be estimated within 30% in this way. This means that estimating the bulk composition of other sections dominated by detrital and biogenic components may require little analytical effort: calcium carbonate contents, average Al contents, and average shale values can be taken from core descriptions, geochemical logs, and the literature, respectively. Some of the geochemical systematics developed at Site 765 can be extrapolated along the entire Sunda Trench. However, results are general, and Site 765 should serve as a useful reference for estimating the compositions of other continental margin sections approaching trenches around the world (e.g., outboard of the Lesser Antilles, Aegean, and Eolian arcs).

Annotated record of the detailed examination of Mn deposits from the R/V Galathea II Danish Deep Sea Expedition, 1950-1952

The Danish Expedition of the "Galathea II" around the world brought important results concerning the marine organisms in the deep sea. The "Galathea II" showed not only different organisms of the Abyssal but for the first time of the deepest trenches of the western Pacific. Anton Bruun coined the term Hadal for the region below the Abyssal under 6000 m. Although the "Galathea II" aimed to investigate new deep sea regions beside the routes of former expeditions and to widen the horizon of knowledge relating marine organisms the technical equipment and the methodological approach had partly been developed earlier. The expedition of the "Galathea II" is part of a long tradition of cruises such as that of the British "Challenger", the German "Valdivia" and the Swedish "Albatross" and especially the Danish cruises of the "Dana I" and "Dana II" which happened some years before.

Composition of Aleutian forearc sediments

The ultimate composition of any sandstone is affected by a host of primary and secondary factors, including the lithologies present in source terranes, climate, depositional environment and diagenesis. In the case of a subduction complex, however, unequivocal identification of detrital provenance may be impossible because of the cumulative effects of tectonic and sedimentary transport. Long-distance sedimentary transport (> 1000 km) is common within trenches, and abyssal-plain turbidites can be tectonically transported for long distances as the underlying oceanic basement drifts towards a subduction front. Post-accretionary displacement can occur as a consequence of strike-slip faulting, and the total distance of tectonic dislocation may reach several thousand kilometers. The present-day Aleutian forearc region (North Pacific Ocean) illustrates many of the "problems" which typify subduction zones. Several petrologic suites can be identified, and there are significant variations in detrital modes in both time and space. The Aleutian region serves as a sobering modern analog for accreted rock units such as the Franciscan Complex of California, where intercalations of discrete sandstone suites have been noted. In the absence of paleomagnetic control, interpretations of sediment provenance within ancient subduction complexes probably should be restricted to the generic level.

(Table 1) d18O of interstitial waters at DSDP Sites 87-582, 87-583, and 87-584

In the present paper, we report preliminary results on the 18O/16O ratios of the interstitial waters of the DSDP cores taken from subduction-related trenches near Japan: Sites 582 and 583 at the Nankai Trough off southwestern Japan, and Site 584 at the Japan Trench off northern Honshu, where thick piles of young sediments have accumulated. Special attention was paid to any differences in isotopic behavior of interstitial waters with different surrounding lithoiogy, the details of isotopic variation of interstitial waters in young, unconsolidated sediments, and the effects of sedimentary structural disturbance on interstitial waters.

Observation of manganese nodules and manganese coated coral in the West Northern Atlantic ocean

Photography has become an integral part of submarine geological and biological investigations of the ocean bottom. The underwater cameras used to make these photographs were designed by Harold Edgerton. The pictures were taken from 1960 to 1962, from ships of the Woods Hole Oceanographic Institution. They show that life occurs even in the deepest trenches, and that sedimentary and biological processes in deep water do not differ in kind from those in shallow water.

A new genus Abyssogena from deep-water vents and seeps

A new genus Abyssogena is established for A. phaseoliformis (Métivier, Okutani & Ohta, 1986) and A. kaikoi (Okutani & Métivier, 1986), which were previously assigned to the genus Calyptogena Dall, 1891, and also for two new species, A. southwardae and A. novacula. The most characteristic features of Abyssogena are an elongate shell up to about 280 mm in length; a pallial line starting from the ventral margin of the anterior adductor scar; secondary pallial attachment scars developed dorsal to the pallial line; radially arranged hinge teeth with a reduced anterior cardinal tooth in the right valve; and presence of an inner ctenidial demibranch only. Abyssogena occurs in deep water from 2,985 to 6,400 m and is distributed in the Pacific and Atlantic Oceans at cold seeps along continental margins and hydrothermal vents at mid-oceanic ridges. Some species have a remarkably wide geographic distribution; A. southwardae is present throughout the Atlantic and A. phaseoliformis is present in Japan, Kuril-Kamchatka, as well as Aleutian Trenches. No fossils of Abyssogena are known.