Geochemical processes and rare earth element analysis in cold-seep pore waters of Hydrate Ridge, northeast Pacific Ocean

The concentrations of rare earth elements (REEs), sulphate, hydrogen sulphide, total alkalinity, calcium, magnesium and phosphate were measured in shallow (<12 cm below seafloor) pore waters from cold-seep sediments on the northern and southern summits of Hydrate Ridge, offshore Oregon. Downward-decreasing sulphate and coevally increasing sulphide concentrations reveal sulphate reductionas dominant early diagenetic process from ~2 cm depth downwards. A strong increase of total dissolved REE concentrations is evident immediately below the sediment-water interface, which can be related to early diagenetic release of REEs into pore water resulting from the remineralization of particulate organic matter. The highest pore water REE concentrations were measured close to the sediment-water interface at ~2 cm depth. Distinct shale normalized REE patterns point to particulate organic matter and iron oxides as main REE sources in the upper ~2-cm depth interval. In general, the pore waters have shalenormalized patterns reflecting heavy REE (HREE) enrichment, which suggests preferential complexation of HREEs with carbonate ions. Below ~2 cm depth, a downward decrease in REE correlates with a decrease in pore water calcium concentrations. At this depth, the anaerobic oxidation of methane (AOM) coupled to sulphate reduction increases carbonate alkalinity through the production of bicarbonate, which results in the precipitation of carbonate minerals. It seems therefore likely that the REEs and calcium are consumed during vast AOM-induced precipitation of carbonate in shallow Hydrate Ridge sediments. The analysis of pore waters from Hydrate Ridge shed new light on early diagenetic processes at cold seeps, corroborating the great potential of REEs to identify geochemical processes and to constrain environmental conditions.

Current velocities and settling experimental results

This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500 km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Phosphorus partition and acumulation rates in sediments of ODP Legs 130 and 138

Understanding phosphorus (P) geochemistry and burial in oceanic sediments is important because of the role of P for modulating oceanic productivity on long timescales. We investigated P geochemistry in seven equatorial Pacific sites over the last 53 Ma, using a sequential extraction technique to elucidate sedimentary P composition and P diagenesis within the sediments. The dominant P-bearing component in these sediments is authigenic P (61-86% of total P), followed in order of relative dominance by iron-bound P (7-17%), organic P (3-12%), adsorbed P (2-9%), and detrital P (0-1%). Clear temporal trends in P component composition exist. Organic P decreases rapidly in younger sediments in the eastern Pacific (the only sites with high sample resolution in the younger intervals), from a mean concentration of 2.3 µmol P/g sediment in the 0-1 Ma interval to 0.4 µmol/g in the 5- 6 Ma interval. Over this same time interval, decreases are also observed for iron-bound P (from 2.1 to 1.1 µmol P/g) and adsorbed P (from 1.5 to 0.7 µmol P/g). These decreases are in contrast to increases in authigenic P (from 6.0-9.6 µmol P/g) and no significant changes in detrital P (0.1 µmol P/g) and total P (12 µmol P/g). These temporal trends in P geochemistry suggest that (1) organic matter, the principal shuttle of P to the seafloor, is regenerated in sediments and releases associated P to interstitial waters, (2) P associated with iron-rich oxyhydroxides is released to interstitial waters upon microbial iron reduction, (3) the decrease in adsorbed P with age and depth probably indicates a similar decrease in interstitial water P concentrations, and (4) carbonate fluorapatite (CFA), or another authigenic P-bearing phase, precipitates due to the release of P from organic matter and iron oxyhydroxides and becomes an increasingly significant P sink with age and depth. The reorganization of P between various sedimentary pools, and its eventual incorporation in CFA, has been recognized in a variety of continental margin environments, but this is the first time these processes have been revealed in deep-sea sediments. Phosphorus accumulation rate data from this study and others indicates that the global pre-anthropogenic input rate of P to the ocean (20x10**10 mol P/yr) is about a factor of four times higher than previously thought, supporting recent suggestions that the residence time of P in the oceans may be as short as 10000-20000 years.

Abundance and sizes of European oak species (Quercus petraea (Matt.) Liebl., Quercus robur L.) in dependence of neighborhood and environmental factors

Quercus robur L. (pedunculate oak) and Quercus petraea (Matt.) Liebl. (sessile oak) are two European oak species of great economic and ecological importance. Even though both oaks have wide ecological amplitudes of suitable growing conditions, forests dominated by oaks often fail to regenerate naturally. The regeneration performance of both oak species is assumed to be subject to a variety of variables that interact with one another in complex ways. The novel approach of this research was to study the effect of many ecological variables on the regeneration performance of both oak species together and identify key variables and interactions for different development stages of the oak regeneration on a large scale in the field. For this purpose, overstory and regeneration inventories were conducted in oak dominated forests throughout southern Germany and paired with data on browsing, soil, and light availability. The study was able to verify the assumption that the occurrence of oak regeneration depends on a set of variables and their interactions. Specifically, combinations of site and stand specific variables such as light availability, soil pH and iron content on the one hand, and basal area and species composition of the overstory on the other hand. Also browsing pressure was related to oak abundance. The results also show that the importance of variables and their combinations differs among the development stages of the regeneration. Light availability becomes more important during later development stages, whereas the number of oaks in the overstory is important during early development stages. We conclude that successful natural oak regeneration is more likely to be achieved on sites with lower fertility and requires constantly controlling overstory density. Initially sufficient mature oaks in the overstory should be ensured. In later stages, overstory density should be reduced continuously to meet the increasing light demand of oak seedlings and saplings.

Chemical, isotope and mineral composition of hydrothermally altered upper oceanic crust drilled at ODP Site 129-801C

ODP Hole 801C penetrates >400 m into 170-Ma oceanic basement formed at a fast-spreading ridge. Most basalts are slightly (10-20%) recrystallized to saponite, calcite, minor celadonite and iron oxyhydroxides, and trace pyrite. Temperatures estimated from oxygen isotope data for secondary minerals are 5-100°C, increasing downward. At the earliest stage, dark celadonitic alteration halos formed along fractures and celadonite, and quartz and chalcedony formed in veins from low-temperature (<100°C) hydrothermal fluids. Iron oxyhydroxides subsequently formed in alteration halos along fractures where seawater circulated, and saponite and pyrite developed in the host rock and in zones of restricted seawater flow under more reducing conditions. Chemical changes include variably elevated K, Rb, Cs, and H2O; local increases in FeT, Ba, Th, and U; and local losses of Mg and Ni. Secondary carbonate veins have 87Sr/86Sr = 0.706337 - 0.707046, and a negative correlation with d18O results from seawater-basalt interaction. Carbonates could have formed at any time since the formation of Site 801 crust. Variable d13C values (-11.2? to 2.9?) reflect the incorporation of oxidized organic carbon from intercalated sediments and changes in the d13C of seawater over time. Compared to other oceanic basements, a major difference at Site 801 is the presence of two hydrothermal silica-iron deposits that formed from low-temperature hydrothermal fluids at the spreading axis. Basalts associated with these horizons are intensely altered (60-100%) to phyllosilicates, calcite, K-feldspar, and titanite; and exhibit large increases in K, Rb, Cs, Ba, H2O, and CO2, and losses of FeT, Mn, Mg, Ca, Na, and Sr. These effects may be common in crust formed at fast-spreading rates, but are not ubiquitous. A second important difference is that the abundance of brown oxidation halos along fractures at Site 801 is an order of magnitude less than at some other sites (2% vs. 20-30%). Relatively smooth basement topography (<100 m) and high sedimentation rate (8 m/Ma) probably restricted the access of oxygenated seawater. Basement lithostratigraphy and early low-temperature hydrothermal alteration and mineral precipitation in fractures at the spreading axis controlled permeability and limited later flow of oxygenated seawater to restricted depth intervals.

Major element and cadmium contents in phosphorites from Pacific seamounts

Cadmium contents in studied rocks from Pacific seamounts usually lower than both in biogenic-diagenetic shelf phosphorites and in pelagic sedimentatary-diagenetic Fe-Mn nodules. In general, the behavior of Cd in phosphorites, phosphatized rocks and iron-manganese-phosphate crusts from the seamounts shows that phosphorus, iron, and manganese are apparently of normal sedimentary origin.

Homogenization of Portuguese long-term temperature data series: Lisbon, Coimbra and Porto

Three long-term temperature data series measured in Portugal were studied to detect and correct non-climatic homogeneity breaks and are now available for future studies of climate variability. Series of monthly minimum (Tmin) and maximum (Tmax) temperatures measured in the three Portuguese meteorological stations of Lisbon (from 1856 to 2008), Coimbra (from 1865 to 2005) and Porto (from 1888 to 2001) were studied to detect and correct non-climatic homogeneity breaks. These series together with monthly series of average temperature (Taver) and temperature range (DTR) derived from them were tested in order to detect homogeneity breaks, using, firstly, metadata, secondly, a visual analysis and, thirdly, four widely used homogeneity tests: von Neumann ratio test, Buishand test, standard normal homogeneity test and Pettitt test. The homogeneity tests were used in absolute (using temperature series themselves) and relative (using sea-surface temperature anomalies series obtained from HadISST2 close to the Portuguese coast or already corrected temperature series as reference series) modes. We considered the Tmin, Tmax and DTR series as most informative for the detection of homogeneity breaks due to the fact that Tmin and Tmax could respond differently to changes in position of a thermometer or other changes in the instrument's environment; Taver series have been used, mainly, as control. The homogeneity tests show strong inhomogeneity of the original data series, which could have both internal climatic and non-climatic origins. Homogeneity breaks which have been identified by the last three mentioned homogeneity tests were compared with available metadata containing data, such as instrument changes, changes in station location and environment, observing procedures, etc. Significant homogeneity breaks (significance 95% or more) that coincide with known dates of instrumental changes have been corrected using standard procedures. It was also noted that some significant homogeneity breaks, which could not be connected to the known dates of any changes in the park of instruments or stations location and environment, could be caused by large volcanic eruptions. The corrected series were again tested for homogeneity: the corrected series were considered free of non-climatic breaks when the tests of most of monthly series showed no significant (significance 95% or more) homogeneity breaks that coincide with dates of known instrument changes. Corrected series are now available in the frame of ERA-CLIM FP7 project for future studies of climate variability.

Mineralogical composition, copper and d18O at DSDP Site 59-448

Alteration in a submarine remnant volcanic arc should leave an important record of (1) the mineralogy of sea water-volcanic arc rock interaction; (2) the chemistry of solid reaction products; (3) the isotopic characteristics of such reactions (Muehlenbachs and Clayton, 1972; Spooner, Beckinsale, et al , 1977; Spooner, Chapman, et al., 1977); (4) the metallogenesis within such a sequence (Mitchell and Bell, 1973); and (5) the geothermal gradient during the alteration. The volcaniclastic breccias, tuffs, and igneous units of Sites 448 (993 m) and 451 (930.5 m) on the Palau-Kyushu and West Mariana ridges, respectively, are particularly suited for such studies because the thick sequences have remained submarine throughout their history, seemingly unaffected by magmatic or hydrothermal events after cessation of volcanic activity. Also, shipboard observations indicated a change in alteration products with depth. At both sites the igneous units and volcaniclastic rocks were altered to brownish clays and zeolites near the top of the volcanic sequence; to bright blue green clays and zeolites at moderate depths; and to very dark, nearly opaque, forest green clays and zeolites at still greater depths. Native copper occurs both as disseminated pockets in the volcaniclastic breccias and vesicular basalts and as veins in the breccias; native copper is restricted to stratigraphic levels characterized by the absence of sulfides or oxides of copper and iron. Although some native copper is found in vesicles of basalts and may be orthomagmatic, most of it is clearly secondary. Near dikes and sills, higher sulfur fugacity conditions caused the precipitation of iron and copper sulfides with an absence of native copper (Garrels and Christ, 1965). The occurrence of native copper may be an initial stage of Cu metallogenesis that forms porphyry coppers in island arcs (Mitchell and Bell, 1973). This study will address primarily the possibility that hydrothermal sea water interaction with volcanic arc rocks has created the mineralogical and isotopic zonation in Leg 59 cores. Hydrothermal activity can be expected in a rapidly growing island arc and is probably the result of a high geothermal gradient prevalent during arc magmatic activity. The chemical character of the alteration is further discussed by Hajash (1981).

Phosphorus components, CaCO3 and biogenic opal in sediments from ODP Leg 167 sites

The ocean history of reactive phosphorus (P) (i.e., dissolved P available to fuel oceanic primary productivity) is of interest because of the role of P as a biolimiting nutrient, and knowledge of P burial in marine sediments is key to testing hypotheses about temporal changes in P input or output fluxes. Our understanding of the history of the P cycle over the Cenozoic has increased substantially with temporal records of reactive P mass accumulation rates from open-ocean Pacific and Atlantic equatorial sites. However, questions about the relative importance of nutrient burial in ocean-margin sediments relative to burial in open-ocean sediments and about the extent of P remobilization in organic-rich, reducing environments characteristic of margin sediments remain unresolved. Nutrient burial in oceanic boundary current systems has been suggested to have a controlling role in oceanic nutrient budgets in certain time intervals (Vincent and Berger, 1985, doi:10.1029/GM032p0455), with higher sediment accumulation rates balancing the limited spatial extent of these sediments. Some investigators suggest that remobilization of P from reducing sediments in margin settings is a significant positive feedback to primary productivity (e.g., Van Cappellan and Ingall, 1994, doi:10.1029/94PA01455), whereas other results indicate that both P uptake and P release may occur in these settings depending on the balance of organic carbon and iron supply to the sediments and on the oxygenation of bottom waters (McManus et al., 1997, doi:10.1016/S0016-7037(97)00138-5). It is important to quantitatively understand the geochemistry of reactive P in margin sediments, where productivity and delivery of organic-rich material to the sediments in relatively shallow-water settings is often sufficient to promote anoxia in interstitial waters. To address these questions, we determined the P concentrations and geochemistry in sediment samples from eight sites drilled during Ocean Drilling Program (ODP) Leg 167, California margin (Sites 1010-1012, 1014, 1016-1017, and 1021-1022). These results are the first records of reactive P concentrations on long time scales-required for the calculation of P accumulation rates-for sediments from a highly productive eastern boundary current setting. In addition, we determined calcium carbonate contents and biogenic silica concentrations to define the environments of sedimentary production, burial, and diagenesis.

Trace metal concentration and age model of ODP Hole 165-1002C sediments

Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene 'thermal maximum'. Since ~5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the 'Little Ice Age'. These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.

Hydrography and water chemistry of the open Mediterranean Sea

On a cruise from the eastern into western Mediterranean Sea in November/December 1978 a total of 126 samples were collected from 8 vertical profiles and 7 coastal stations for trace metal analysis. The sampling, processing and analysis was performed under strict "clean room" conditions. The concentration of the open-sea samples are close to oceanic results gathered under similar conditions. The grand averages from all profiles (± st. dev. of the individual samples) of 0.40 ± 0.16 µg/l Zn, 17.4 ± 7.4 ng/l Cd, 0.21 ± 0.07 µg/l Cu, 0.21 ± 0.13 µg/l Mn and 0.25 ± 0.09 µg/l Fe indicate that a "metal problem" does not exist in the open Mediterranean. A biologically mediated deplition in surface waters or correlation with nutrients have not been observed under the conditions established on this cruise. This is probably due top low primary production and seasonal advection processes prevailing in this sea. The data for manganese show generally higher values in the surface layer (0-75 m) than in deep waters. This could evidently proved in the nearshore profile indicating a terrigenous source for manganese.

Geochemical analysis of bulk sediment and interstitial water of sediment cores from the North-West African continental margin

Molybdenum and vanadium were analysed in 9 scediment cores recovered from the continental slope and rise off NW Africa. Additionall chemical and sedimentological parameters as well as isotope stage boundaries were available for the same core profiles from other investigations. Molybdenum, ranging between <1 and 10 ppm, occurs in two associateions, either with organic carbon and sulphides in sediments with reducing conditions or with Mn oxides in oxidized near-surface core sections. Highest values (between 4 and 10 ppm Mo) are found in sulphide-rich core sections deposited during glacial times in a core from 200 m water depth. The possibility of anoxic near-bottom water conditions prevailing at thhis site during certain glacial intervals is discussed. In oxidized near-surface core sections, the diagenetic mobility of Mo becomes evident from strong Mo enrichment together with Mn oxides (values up to 4 ppm Mo). This enrichment is probably due to coprecipitation and/or adsorption of Mo from interstitial water to the diagenetically forming Mn oxides. The close relation between Mo and Corg results in strongly covarying sedimentation rates in both components reaching up to 10 times the rates in glacial compared to interglacial core sections. Vanadium (values between 20 and 100 ppm) does not show clear relations to climate and near-bottom or sediment milieu. It occurs mainly bound to the fine grained terrigenous fraction, associated with aluminium silicates (clay minerals) and iron oxides. Additionally positive covariation of vanadium with phosphorus in most core profiles suggest that some V may be bound to phosphates.

Sedimentary facies, clay mineralogy and geochemistry of the Paleogene sediments of ODP Site 105-647

Claystones immediately overlying the early Eocene age ocean-floor basalt, cored at Ocean Drilling Program (ODP) Site 647, underwent hydrothermal and thermal alterations originating from the basalt, which resulted in changes in both the mineralogical and chemical composition of the sediments. Chlorites and higher magnesium and iron concentrations were found in the lowermost sediment sequence. Upcore, changes in the bulk chemical composition of the sediments become smaller, when compensated for variations in the carbonate content originating from biogenic and authigenic components. Chlorite disappears upcore, but still only part of the swelling clay minerals have survived the thermal influence. Thirty meters above the basalt, the clay mineralogy and chemical composition become uniform throughout the Paleogene section. Iron-rich smectites (i.e., nontronitic types), totally dominate the clay mineral assemblage. Biogenic components, responsible for the dominant part of the calcite and cristobalite contents, vary in amount in the upper part, and so do the authigenic carbonate and sulfide contents. Detrital components, such as kaolinite, illite, quartz, and feldspars, make up a very small proportion of the sediment record. The nontronitic smectites are believed to be authigenic, formed by a supply of iron from the continuous formation of ocean-floor basalt in the ridge area that reacted with the detrital and biogenic silicates and alumina silicates.