Chemical and isotopic analysis of bulk organic matter and hydrocarbon biomarkers from IODP Holes 311-U1327C, 311-U1328B and 311-U1328C

The chemical and isotopic compositions of sedimentary organic matter (SOM) from two mid-slope sites of the northern Cascadia margin were investigated during Integrated Ocean Drilling Program (IODP) Expedition 311 to elucidate the organic matter origins and identify potential microbial contributions to SOM. Gas hydrate is present at both locations (IODP Sites U1327 and U1328), with distinct patterns of near-seafloor structural accumulations at the cold seep Site U1328 and deeper stratigraphic accumulations at the slope-basin Site U1327. Source characterization and evidence that some components of the organic matter have been diagenetically altered are determined from the concentrations and isotopic compositions of hydrocarbon biomarkers, total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS). The carbon isotopic compositions of TOC (d13C TOC = -26 to -22 per mil) and long-chain n-alkanes (C27, C29 and C31, d13C = -34 to -29 per mil) suggest the organic matter at both sites is a mixture of 1) terrestrial plants that employ the C3 photosynthetic pathway and 2) marine algae. In contrast, the d15N TN values of the bulk sediment (+4 to +8 per mil) are consistent with a predominantly marine source, but these values most likely have been modified during microbial organic matter degradation. The d13C values of archaeal biomarker pentamethylicosane (PMI) (-46.4 per mil) and bacterial-sourced hopenes, diploptene and hop-21-ene (-40.9 to -34.7 per mil) indicate a partial contribution from methane carbon or a chemoautotrophic pathway. Our multi-isotope and biomarker-based conclusions are consistent with previous studies, based only on the elemental composition of bulk sediments, that suggested a mixed marine-terrestrial organic matter origin for these mid-slope sites of the northern Cascadia margin.

(Table 1) Chemical composition of volcanic rocks from the Mariisky sequence and extrusive vent rocks of the Mary Cape, Schmidt Peninsula (North Sakhalin)

Early Cretaceous volcanic rocks of the Mariisky sequence and Early Cenozoic extrusive-vent rocks of the Mary Cape are exposed at the most northwest of the Schmidt Peninsula, North Sakhalin. In chemical composition, all the rocks are subdivided into four groups. Three groups include volcanic rocks of the Mariisky sequence, which consists, from bottom to top, of calc-alkaline rocks, transitional calc-alkaline-tholeiite rocks, and incompatible element-depleted tholeiites. These rocks show subduction geochemical signatures and are considered as a fragment of the Moneron-Samarga island arc system. Trace-element modeling indicates their derivation through successive melting of a garnet-bearing mantle and garnet-free shallower mantle sources containing amphibole; pyroxene; and, possibly, spinel. The mixed subduction and intra-plate characteristics of the extrusive vent rocks of the Mary Cape attest to their formation in a transform continental margin setting.

Physical, chemical and geological properties of sediments from the central equatorial Pacific

The solution rate of biogenic opal in near-surface sediments in the Central Equatorial Pacific is three to eight orders of magnitude lower than similar acid-cleaned samples. Iron, magnesium and calcium aluminosilicates may be the minerals which are forming on the surface of the opal and reducing its solution rate. The scale height of the system studied suggests that diffusive and not advective processes are primarily responsible for the removal of dissolved silica in sediments. Solution budget calculations for this area suggest that 90-99 per cent of the biogenic opal produced in surface waters dissolves before reaching the sediment-water interface; an additional amount dissolves within the sediment and diffuses into bottom waters leaving 0.05-0.15 per cent of the original amount of opal produced by organisms in the sedimentary record. The relative solution potential of the upper 1000 m of the water column varies by more than an order of magnitude from the Antarctic to Equator and may have a pronounced effect on the accumulation rate of biogenic opal in underlying sediments.

Chemical composition of altered volcanic rocks from ODP Sites 193-1188 and 193-1189

The conventional model of leaching volcanic rocks as a source of metals in a seafloor hydrothermal systems has been tested by examining the behavior of Pb and other trace elements during hydrothermal alteration. ODP Leg 193 drill sites 1188 (Snowcap) and 1189 (Roman Ruins) on Pual Ridge in the eastern Manus Basin offshore eastern Papua New Guinea provide a unique three-dimensional window into an active back-arc hydrothermal system. We investigate by means of a LA-ICP-MS microbeam technique the capacity of Pb to be leached from a host volcanic rock exposed to various types and intensities of alteration. Our results are in general agreement with previous studies that utilized bulk analytical techniques but provide a more detailed explanation of the processes. Fresh representative dacitic lavas from the Pual Ridge have an average whole rock Pb content of 5.2 ppm, an average interstitial glass Pb content of 5.6 ppm and an average plagioclase Pb content of 1.0 ppm. Altered matrix samples have highly variable Pb values ranging from 0 to 52.4 ppm. High Pb values in altered samples are associated with a low temperature chlorite and clay mineral assemblage, in some cases overprinted by a high temperature (up to 350°C) silica-rich "bleaching" alteration. Only the most highly altered matrix samples have REE patterns that differ from the fresh Pual Ridge dacite. This may represent either different lava histories or alteration characteristics that have affected normally immobile REEs. Altered samples with the highest Pb values have similar REE patterns to those of the local unaltered lavas. They are compositionally similar to typical Pual Ridge dacites indicating a genetic relationship between the main regional volcanic suite and the subseafloor hydrothermally altered, Pb-enriched material. Relative loss/gain for Pb between the analyzed altered samples and a calculated precursor show a maximum relative gain of 901%. Samples with relative Pb gain from both drill sites are associated with lower temperature alteration mineral assemblages characterized by pervasive chloritization. The related lower temperature (220-250°C) neutral to slightly acidic fluids have been ascribed by others to return circulation of hydrothermal fluids that did not interact with seawater. Because altered samples have a higher Pb content than the fresh precursor, leaching of fresh volcanic rocks cannot be the source of Pb in the hydrothermal systems.

Mineral and chemical composititon of sediments from ODP Hole 119-740A

ODP Hole 740A is located on the inner part of the East Antarctic continental shelf in Prydz Bay, at the seaward end of a major onshore rift structure known as the Lambert Graben. Drilling at this site led to the recovery of some 65 m of continental sediments (Prydz Bay red beds) that form part of a much thicker (2-3 km) pre-continental breakup sequence, the development of which may be related to the initiation and rifting of the Lambert Graben. Palynological and paleomagnetic studies have not been able to determine the age of the sediments; they may be equivalent to the onshore late Permian Amery Group or younger. The succession consists predominantly of sandstone, siltstone, and claystone arranged in erosively based, pedogenically influenced fining-upward sequences up to 5 m thick. These were deposited by shallow, braided streams draining an extensively vegetated alluvial plain, with sufficient topographic relief to trap fine-grained sediment and inhibit rapid channel shifting. Pedogenic processes were initiated on the alluvial plain, but climatic conditions were generally unsuitable for extensive pedogenic carbonate formation and the development of mature soil profiles. The sediments were probably derived from a rapidly uplifted fault block terrain composed of upper Proterozoic and Archaean gneisses lying to the southeast of the depositional site. Uplift may have taken place along the tectonically active seaward extension of the eastern faulted margin of the Lambert Graben, which passes immediately southeast of Hole 740A. Differences in mineralogical composition between the Amery Group and the Prydz Bay red beds probably reflect differences in rock composition in the source area. The age of the Prydz Bay red beds has still to be resolved.

Chemical element concentrations in sediments from DSDP Holes 60-458 and 60-459

The development of laser ablation-inductively coupled plasma-mass spectrometry has revolutionized the analysis of tephras by providing (1) an efficient and precise method for determining abundances of a wide variety of trace elements at low concentrations in individual glass shards and (2) assessment of geochemical heterogeneities within individual ash horizons. This development is important for petrogenetic studies of intraoceanic arc systems, where tephras provide the most complete temporal record of magmatism. Results from the Izu-Bonin and Mariana arc systems indicate that despite close geographical proximity and similar tectonic evolution, they contrast strongly in terms of geochemical evolution since 35 Ma. Whereas the Mariana tephras have exceptional compositional diversity, ranging from low-K (Oligocene), to high-K (Miocene), and subsequently medium-K compositions (Pliocene-Quaternary), the Izu-Bonin arc has been dominated by low-K compositions throughout. The Mariana increases in K are paralleled by increases in abundances of incompatible trace elements and by increased values of diagnostic ratios (e.g., Nb/yb and Th/yb) regarded as monitors of potential mantle-source fertility. The relative uniformity of Nb/yb and Nb/Zr ratios in Izu-Bonin tephras indicates that cyclic processes of backarc basin development and mantle depletion do not necessarily induce large-scale temporal geochemical variations in the associated arc. Temporal variability within the Mariana arc, and its divergence from the Izu-Bonin arc ca. 13 Ma, can be traced to a major injection of subducted sediment in the Mariana system at this time.

Isotopic and chemical compositions of DSDP site 18-174 sediments

The Astoria submarine fan, located off the coast of Washington and Oregon, has grown throughout the Pleistocene from continental input delivered by the Columbia River drainage system. Enormous floods from the sudden release of glacial lake water occurred periodically during the Pleistocene, carrying vast amounts of sediment to the Pacific Ocean. DSDP site 174, located on the southern distal edge of the Astoria Fan, is composed of 879 m of terrigenous sediments. The section is divided into two major units separated by a distinct seismic discontinuity: an upper, turbidite fan unit (Unit I), and an underlying finer-grained unit (Unit II). Both units have overlapping ranges of Nd and Hf isotope compositions, with the majority of samples having e-Nd values of -7.1 to -15.2 and eHf values -6.2 to -20.0; the most notable exception is the uppermost sample in the section, which is identical to modern Columbia River sediment. Nd depleted mantle model ages for the site range from 2.0 to 1.2 Ga and are consistent with derivation from cratonic Proterozoic source regions, rather than Cenozoic and Mesozoic terranes proximal to the Washington-Oregon coast. The Astoria Fan sediments have significantly less radiogenic Nd (and Hf) isotopic compositions than present day Columbia River sediment (e-Nd=-3 to -4; [Goldstein, S.J., Jacobsen, S.B., 1987. Nd and Sr isotopic systematics of river water suspended material: implications for crustal evolution. Earth. Planet. Sci. Lett. 87, 249-265; doi:10.1016/0012-821X(88)90013-1]), and suggest that outburst flooding, tapping Proterozoic source regions, was the dominant sediment transport mechanism in the genesis and construction of the Astoria Fan. Pb isotopes form a highly linear 207Pb/204Pb - 206Pb/204Pb array, and indicate the sediments are a binary mixture of two disparate sources with isotopic compositions similar to Proterozoic Belt Supergroup metasediments and Columbia River Basalts. The combined major, trace and isotopic data argue that outburst flooding was responsible for depositing the majority (top 630 m) of the sediment in the Astoria Fan.

Chemical composition of surficial bottom sediments from the Chukchi Sea and adjacent part of the Arctic Ocean

This paper presents data on chemical composition of bottom sediments from the Chukchi Sea and the adjacent Arctic Ocean. Multivariate statistical techniques were used for analysis of the data set and revealed that grain size fractionation of the original terrigenous component during sedimentation was the major factor of clustering of the samples in study. Secondary factors include accumulation of biogenic siliceous and carbonate material and chemogenic or biochemical accumulation of iron, manganese, and some trace elements. The latter factor was significant in areas of tectonic activity within the graben-rift system of the Chukchi Sea.

Chemical composition of basalts and basaltic glasses from the Sierra Leone Fracture Zone region

Major and trace element (including REE) geochemistry of basalts and chilled basaltic glasses from the MAR axial zone in the vicinity of the Sierra Leone FZ (5-7°10'N) has been studied. Associations of basalts of various compositions with particular ocean-floor geological structural features have been analyzed as well. Three basaltic varieties have been discriminated. Almost ubiquitous are high-Mg basalts (Variety 1) that are derivatives of N-MORB tholeiitic melts and that are produced in the axial zone of spreading. Variety 2 is alkaline basalts widespread on the southwestern flank of the MAR crest zone in the Sierra Leone region, likely generated through deep mantle melting under plume impact. Variety 3 is basalts derivative from T- and P-MORB-like tholeiitic melts and originating through addition of deeper mantle material to depleted upper mantle melts. Magma generation parameters, as calculated from chilled glass compositions, are different for depleted tholeiites (44-55 km, 1320-1370°C) and enriched tholeiites (45-78 km, 1330-1450°C). Mantle plume impact is shown to affect not only tholeiitic basalt compositions but also magma generation conditions in the axial spreading zone, resulting in higher Ti and Na concentrations in melts parental to rift-related basalts occurring near the plume. T- and P-MORBs are also developed near areas where mantle plumes are localized. High-Mg basalts are shown to come in several types with distinctive Ti and Na contents. Nearly every single MAR segment (bounded by sinistral strike slips and the Bogdanov Fracture Zone) is featured by its own basalt type suggesting that it has formed above an asthenospheric diapir with its unique magma generation conditions. These conditions are time variable. Likely causes of temporal and spatial instability of the mantle upwelling beneath this portion of the MAR are singular tectonic processes and plume activity. In sulfide-bearing rift morphostructures (so-called "Ore area'' and the Markov Basin), basalts make up highly evolved suites generated through olivine and plagioclase fractionation, which is suggestive of relatively long-lived magma chambers beneath the sulfide-bearing rift morphostructures. Functioning of these chambers is a combined effect of singular geodynamic regime and plume activity. In these chambers melts undergo deep differentiation leading to progressively increasing concentration of sulfide phase, eventually to be supplied to the hydrothermal plumbing system.

Chemical composition of rocks and minerals from the Karymsky volcanic center, Eastern Kamchatka

The powerful eruption in the Akademii Nauk caldera on January 2, 1996 marked a new activity phase of the Karymsky volcano and became a noticeable event in the history of modern volcanism in Kamchatka. The paper reports data obtained by studying more than 200 glassy melt inclusions in phenocrysts of olivine (Fo82-72), plagioclase (An92-73), and clinopyroxene (Mg# 83-70) in basalts of the 1996 eruption. The data were used to estimate composition of the parental melt and physicochemical parameters of the magma evolution. According to our data, the parental melt corresponded to low magnesium, high aluminum basalt (SiO2 = 50.2%, MgO = 5.6%, Al2O3 = 17%) of the mildly potassium type (K2O = 0.56%) and contained much dissolved volatile components (H2O = 2.8%, S = 0.17%, and Cl = 0.11%). Melt inclusions in the minerals are similar in chemical composition, a fact testifying that the minerals crystallized simultaneously with one another. Their crystallization started at pressure ~1.5 kbar, proceeded within a narrow temperature range of 1040+/-20°C, and continued until near-surface pressure ~100 bar was reached. Degree of crystallization of the parental melt during its eruption was close to 55%. Massive crystallization was triggered by H2O degassing under pressure <1 kbar. Magma degassing in an open system resulted in escape of 82% H2O, 93% S, and 24% Cl (of their initial contents in the parental melt) to the fluid phase. Release of volatile compounds to the atmosphere during the eruption that lasted for 18 h was estimated as 1.7x10**6 t H2O, 1.4x10**5 t S, and 1.5x10**4 t Cl. Concentrations of most incompatible trace elements in the melt inclusions are close to those in the rocks and to the expected fractional differentiation trend. Melt inclusions in plagioclase were found to be selectively enriched in Li. The Li-enriched plagioclase with melt inclusions thought to originate from cumulate layers in the feeding system beneath Karymsky volcano, in which plagioclase interacted with Li-rich melts/brines and was subsequently entrapped and entrained by the magma during the 1996 eruption.

Biological, physical and chemical characteristics of water and sediment samples from the Volga River delta, northern Caspian

Based on the data of synchronous observations of hydrophysical and biogeochemical parameters in the near-mouth and shallow-water areas of the northern Caspian in 2000-2001, the scale of spatiotemporal variability in the following characteristics of the water-bottom system was estimated (1) flow velocity and direction within vortex structures formed by the combined effect of wind, discharge current, and the presence of higher aquatic plants; (2) dependence of the spatial distribution of the content and composition of suspended particulate matter on the hydrodynamic regime of waters and development of phytoplankton; (3) variations in the grain-size, petrographic, mineralogical, and chemical compositions of the upper layer of bottom sediments at several sites in the northern Caspian related to the particular local combination of dominant natural processes; and (4) limits of variability in the group composition of humus compounds in bottom sediments. The acquired data are helpful in estimating the geochemical consequences of a sea level rise and during the planning of preventive environmental protection measures in view of future oil and gas recovery in this region.

Chemical and germanium isotopic compositions of sediments and sedimentary rocks from ODP Sites 129-801 and 185-1149

A new technique for the precise and accurate determination of Ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal. The analyses were performed using a continuous flow hydride generation system coupled to a MC-ICP-MS. Samples have been purified through anion- and cation-exchange resins to separate Ge from matrix elements and eliminate potential isobaric interferences. Variations of 74Ge/70Ge ratios are expressed as d74Ge values relative to our internal standard and the long-term external reproducibility of the data is better than 0.2? for sample size as low as 15 ng of Ge. Data are presented for igneous and sedimentary rocks, and the overall variation is 2.4? in d74Ge, representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of Ge is not unique. Co-variations of 74Ge/70Ge, 73Ge/70Ge and 72Ge/70Ge ratios follow a mass-dependent behaviour and imply natural isotopic fractionation of Ge by physicochemical processes. The range of d74Ge in igneous rocks is only 0.25? without systematic differences among continental crust, oceanic crust or mantle material. On this basis, a Bulk Silicate Earth reservoir with a d74Ge of 1.3+/-0.2? can be defined. In contrast, modern biogenic opal such as marine sponges and authigenic glauconite displayed higher d74Ge values between 2.0? and 3.0?. This suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the d74Ge of the seawater to +3.0?.This suggests that seawater is isotopically heavy relative to Bulk Silicate Earth and that biogenic opal may be significantly fractionated with respect to seawater. Deep-sea sediments are within the range of the Bulk Silicate Earth while Mesozoic deep-sea cherts (opal and quartz) have d74Ge values ranging from 0.7? to 2.0?. The variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz. Further work is now required to determine Ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification.

Chemical and boron isotopic compositions of volcanics from ODP Sites 135-834 to 135-840

The influence of fluid flux on petrogenesis in the Tonga-Kermadec Arc was investigated using ion microprobe measurements of B/Be and boron isotope ratios (11B/10B) to document the source and relative volumes of the fluids released from the subducting oceanic plate. We analyzed young lavas from eight different islands along the Tonga-Kermadec Arc, as well as glass shards in volcanic sediments from Ocean Drilling Program (ODP) Site 840, which record the variations in the chemistry of Tonga magmatism since 7 Ma. B/Be is variable (5.8-122), in young Tonga-Kermadec Arc lavas. In contrast, glass shards from around 3 to 4 Ma old volcanic sediments at Site 840 have the highest B/Be values yet reported for arc lavas (18-607). These values are too high to be related simply to a sediment influence on petrogenesis. Together with very high d11B values (-11.6 to +37.5) for the same shards and lavas these data indicate that most of the B is derived from fluid escaped from the subducting altered Pacific oceanic crust, rather than from sediment. High d11B values also reflect large degrees of isotopic fractionation in this cold fast subduction zone. Lower d11B values noted in the Kermadec Arc (17 to -4.4) are related to the influence of sediment eroded from New Zealand and slower convergence. High fluid flux (B/Be) is synchronous in Tonga and the Marianas at 3 to 4 Ma and may be related to acceleration of the Pacific Plate just prior to this time. The timing of maximum B/Be at 3 to 4 Ma correlates with maximum light rare earth (LREE) and high field strength element depletion. This suggests maximum degrees of partial melting at this time. Although thinning of the arc lithosphere during rifting to form the Lau Basin is expected to influence the arc geochemistry, variable aqueous fluid flux from the subducting plate alone appears capable of explaining boron and other trace element systematics in the Tonga-Kermadec Arc with no indication of slab melting.

(Supplemental Table 2) Plant characteristics, GHG fluxes, and soil chemical and microbial properties in experimental treatments in Alexandra Fiord

We evaluated above- and belowground ecosystem changes in a 16 year, combined fertilization and warming experiment in a High Arctic tundra deciduous shrub heath (Alexandra Fiord, Ellesmere Island, NU, Canada). Soil emissions of the three key greenhouse gases (GHGs) (carbon dioxide, methane, and nitrous oxide) were measured in mid-July 2009 using soil respiration chambers attached to a FTIR system. Soil chemical and biochemical properties including Q10 values for CO2, CH4, and N2O, Bacteria and Archaea assemblage composition, and the diversity and prevalence of key nitrogen cycling genes including bacterial amoA, crenarchaeal amoA, and nosZ were measured. Warming and fertilization caused strong increases in plant community cover and height but had limited effects on GHG fluxes and no substantial effect on soil chemistry or biochemistry. Similarly, there was a surprising lack of directional shifts in the soil microbial community as a whole or any change at all in microbial functional groups associated with CH4 consumption or N2O cycling in any treatment. Thus, it appears that while warming and increased nutrient availability have strongly affected the plant community over the last 16 years, the belowground ecosystem has not yet responded. This resistance of the soil ecosystem has resulted in limited changes in GHG fluxes in response to the experimental treatments.