(Table 1) Sulfur isotopes, total sulfur, and degree of oxidation of basalt samples from DSDP Holes 69-504B and 70-504B

Whole-rock basalt samples from the upper half of Deep Sea Drilling Project Hole 504B have oxygen-isotope compositions typical of mid-ocean-ridge basalts which have experienced a moderate degree of low-temperature alteration by sea water. By contrast, d18O values in the lower half of the hole correspond to basalts which have experienced almost no detectable oxygen-isotope alteration. These observations suggest that the overall water/rock ratio was lower in the lower half of the drilled crust. A correlation between d18O values and 87Sr/86Sr ratios suggests that the water/rock ratio, rather than temperature variation, was the main factor determining basalt d18O values. Hydrogen-isotope data appear to be consistent with a low water/rock ratio in the lower part of the crust.

(Appendix 1-4) Geochemistry, desorption methods, TOC, TC, and mineral content of different settings

Sorption of volatile hydrocarbon gases (VHCs) to marine sediments is a recognized phenomenon that has been investigated in the context of petroleum exploration. However, little is known about the biogeochemistry of sorbed methane and higher VHCs in environments that are not influenced by thermogenic processes. This study evaluated two different extraction protocols for sorbed VHCs, used high pressure equipment to investigate the sorption of methane to pure clay mineral phases, and conducted a geochemical and mineralogical survey of sediment samples from different oceanographic settings and geochemical regimes that are not significantly influenced by thermogenic gas. Extraction of sediments under alkaline conditions yielded higher concentrations of sorbed methane than the established protocol for acidic extraction. Application of alkaline extraction in the environmental survey revealed the presence of substantial amounts of sorbed methane in 374 out of 411 samples (91%). Particularly high amounts, up to 2.1 mmol kg**-1 dry sediment, were recovered from methanogenic sediments. Carbon isotopic compositions of sorbed methane suggested substantial contributions from biogenic sources, both in sulfate-depleted and sulfate-reducing sediments. Carbon isotopic relationships between sorbed and dissolved methane indicate a coupling of the two pools. While our sorption experiments and extraction conditions point to an important role for clay minerals as sorbents, mineralogical analyses of marine sediments suggest that variations in mineral composition are not controlling variations in quantities of sorbed methane. We conclude that the distribution of sorbed methane in sediments is strongly influenced by in situ production.

Chemical and isotopic compositions of groundwaters in the Badain Jaran Desert, Northern China

Despite its extreme aridity the Badain Jaran Desert is rich in groundwater. In the southeastern part of this desert it is characterized by coexistence of high megadunes and a great number of lakes. Deuterium and oxygen 18 isotope compositions as well as hydrochemistry of groundwater, lake water, soil water and river water were investigated in detail to gain an insight into their relationships and the origin of the groundwater. The results show that the groundwater and the lake water are genetically related, but unrelated to local precipitation and the leakage of Heine River at the northern slope of the Qilian mountain. dD and d18O values of deep soil water (deeper than 40 cm) and groundwater plot on the same evaporation line E11, which shows that they have the same recharge source. The point of intersection between E11 and LMWL suggests that the groundwater originates from a water resource, which has a weighted mean value that is lighter by some 6 per mil d18O than local precipitation in Badain Jaran Desert. 3H data of water samples show that the groundwater in the Badain Jaran Desert originates from water recharged after the nuclear test. The deep fault zone underground maybe a water circulation channel based on helium analysis of groundwater. The result has guiding significance to rational exploitation and utilization of the local groundwater.

Seasonal changes in the D/H ratio of fatty acids of pelagic microorganisms

Culture studies of microorganisms have shown that the hydrogen isotopic composition of fatty acids depends on their metabolism, but there are only few environmental studies available to confirm this observation. Here we studied the seasonal variability of the deuterium/hydrogen (D/H) ratio of fatty acids in the coastal Dutch North Sea and compared this with the diversity of the phyto- and bacterioplankton. Over the year, the stable hydrogen isotopic fractionation factor epsilon between fatty acids and water ranged between -172 per mil and -237 per mil, the algal-derived polyunsaturated fatty acid nC20:5 being the most D-depleted and nC18:0 the least D-depleted fatty acid. The D-depleted nC20:5 is in agreement with culture studies, which indicates that photoautotrophic microorganisms produce fatty acids which are significantly depleted in D relative to water. The epsilon-lipid/water of all fatty acids showed a transient shift towards increased fractionation during the spring phytoplankton bloom, indicated by increasing chlorophyll a concentrations and relative abundance of the nC20:5 PUFA, suggesting increased contributions of photoautotrophy. Time periods with decreased fractionation (less negative epsilon-lipid/water values) can be explained by an increased contribution by heterotrophy to the fatty acid pool. Our results show that the hydrogen isotopic composition of fatty acids is a useful tool to assess the community metabolism of coastal plankton.

Determination of hydrocarbon gases in mud volcanoes in the Sorokin Trough

Hydrocarbon gases were determined in sediments from three mud volcanoes in the Sorokin Trough. In comparison to a reference station outside the mud volcano area, the deposits are characterized by an enrichment of high-molecular hydrocarbons (C2-C4), an absence of unsaturated homologues, a predominance of iso-butane in comparison with n-butane, and the presence of gas hydrate. The molecular composition of the hydrocarbon gases suggests their deep sources and thermogenic origin. In the pelagic sediments at the reference station, the methane concentration is relatively low (up to 49 ml/l); maximum concentrations are reached in deposits of the Dvurechenskii mud volcano (up to 400 ml/l). It was the first time that gas hydrate was sampled at the Dvurechenskii mud volcano. The gas extracted by dissociation of hydrate samples was dominated by methane (99.5%) with low amounts of ethane and propane (less than 0.5%). The isotopic composition of the methane varies between -62 and -66 per mill PDB in d13C, and between -185 and -209 per mill SMOW in dD, indicating a mainly biogenic origin with an admixture of thermogenic gas.

Chemical and isotopic composition of seawater and waters from thermal spring sites of the Yankicha Island and Kraternaya Bay

A study of chemical and isotopic composition of coastal thermal springs and waters of the Kraternaya Bay, Yankicha Island, revealed that the total mineralization and concentrations of d18O and d2H decrease from the thermal spring site I to V. These waters are of marine origin with various proportions of local meteoric water. Thermal waters of the site VI have considerably altered chemical and isotopic composition due to high temperatures of surrounding rocks. Base temperatures calculated for this area were 130-200°C. Coastal thermal springs affect isotopic composition of water throughout the bay.

Oxygen and hydrogen isotopes at DSDP Leg 65 Holes

In order to provide information on the degree of alteration of the very young basaltic basement drilled on Leg 65 in the mouth of the Gulf of California, we have measured the oxygen isotopic composition of whole rocks and mineral separates. Considerable data already exist for older ocean crust, in particular for the deep holes drilled in the Atlantic Ocean on Deep Sea Drilling Project (DSDP) Legs 37, 45, 46, and 51-53. These data indicate that in all of these holes, which include crust as young as 3.5 m.y. old, a significant amount of alteration has taken place as the result of low-temperature interaction between basalt and seawater (cf. Muehlenbachs, 1977, 1980; Hoernes et al., 1978; Friedrichsen and Hoernes, 1980). It is therefore of interest to determine whether Leg 65 crust, which is only 0.5 to 1.5 m.y. old, has experienced a similar degree of alteration.

C and H geochemistry of altered oceanic crus of ODP/IODP Hole 1256D

Carbon and hydrogen concentrations and isotopic compositions were measured in 19 samples from altered oceanic crust cored in ODP/IODP Hole 1256D through lavas, dikes down to the gabbroic rocks. Bulk water content varies from 0.32 to 2.14 wt% with dD values from -64per mil to -25per mil. All samples are enriched in water relative to fresh basalts. The dD values are interpreted in terms of mixing between magmatic water and another source that can be either secondary hydrous minerals and/or H contained in organic compounds such as hydrocarbons. Total CO2, extracted by step-heating technique, ranges between 564 and 2823 ppm with d13C values from -14.9per mil to -26.6per mil. As for water, these altered samples are enriched in carbon relative to fresh basalts. The carbon isotope compositions are interpreted in terms of a mixing between two components: (1) a carbonate with d13C = -4.5per mil and (2) an organic compound with d13C = -26.6per mil. A mixing model calculation indicates that, for most samples (17 of 19), more than 75% of the total C occurs as organic compounds while carbonates represent less than 25%. This result is also supported by independent estimates of carbonate content from CO2 yield after H3PO4 attack. A comparison between the carbon concentration in our samples, seawater DIC (Dissolved Inorganic Carbon) and DOC (Dissolved Organic Carbon), and hydrothermal fluids suggests that CO2 degassed from magmatic reservoirs is the main source of organic C addition to the crust during the alteration process. A reduction step of dissolved CO2 is thus required, and can be either biologically mediated or not. Abiotic processes are necessary for the deeper part of the crust (>1000 mbsf) because alteration temperatures are greater than any hyperthermophilic living organism (i.e. T > 110 °C). Even if not required, we cannot rule out the contribution of microbial activity in the low-temperature alteration zones. We propose a two-step model for carbon cycling during crustal alteration: (1) when "fresh" oceanic crust forms at or close to ridge axis, alteration starts with hot hydrothermal fluids enriched in magmatic CO2, leading to the formation of organic compounds during Fischer-Tropsch-type reactions; (2) when the crust moves away from the ridge axis, these interactions with hot hydrothermal fluids decrease and are replaced by seawater interactions with carbonate precipitation in fractures. Taking into account this organic carbon, we estimate C isotope composition of mean altered oceanic crust at ? -4.7per mil, similar to the d13C of the C degassed from the mantle at ridge axis, and discuss the global carbon budget. The total flux of C stored in the altered oceanic crust, as carbonate and organic compound, is 2.9 ± 0.4 * 10**12 molC/yr.

Geochemistry of pore fluids from ODP Leg 134 sites

Depending on the temperature and the extent of diagenetic alteration of fluid chemistry, fluid flow at convergent margins may transfer important quantities of heat and mass between the crust and seawater, thereby influencing global mass, isotopic and heat budgets. In the North Aoba Basin, an intra-arc basin located at the New Hebrides Island Arc, alteration of volcanic ash to clay minerals and zeolites forms a CaCl2 brine, perhaps in less than 1 to 3 m.y. The brine results from an exchange of Ca for Na, K, and Mg, and an increase in Cl concentrations to a maximum of 1241 mM. The Cl increase is partly due to the transfer of H2O from the pore fluid into authigenic minerals, but water mass balances, d18O-Cl correlations, and Br/Cl ratios suggest that there is a source of Cl in the sediments. Concentration profiles indicate that Li is transferred from the fluid to solid phase at depths <300 meters below seafloor (mbsf), but at greater depths it is transferred from the solid to fluid phase, at temperatures possibly as low as 25°C. In the accretionary wedge extensive fluid flow appears to be confined to highly faulted regions. Although Cl concentrations less than seawater value are common at convergent margins, the New Hebrides margin contains little low-Cl fluid. Br/Cl ratios suggest the low-Cl fluid is from dilution, and d18O values indicate the water may be derived from mineral dehydration and mixing with meteoric water. The New Hebrides margin exhibits few surface manifestations of venting (e.g., sulfide-oxidizing benthic biological communities, carbonate crusts, mud volcanoes) and thus fluid fluxes may be smaller than at many other margins.

Hydrochemistry, water level, and discharge of water from Samoylov Island, Lena Delta, northeastern Siberia, in 2008

Although ponds make up roughly half of the total area of surface water in permafrost landscapes, their relevance to carbon dioxide emissions on a landscape scale has, to date, remained largely unknown. We have therefore investigated the inflows and outflows of dissolved organic and inorganic carbon from lakes, ponds, and outlets on Samoylov Island, in the Lena Delta of northeastern Siberia in September 2008, together with their carbon dioxide emissions. Outgassing of carbon dioxide (CO2) from these ponds and lakes, which cover 25% of Samoylov Island, was found to account for between 74 and 81% of the calculated net landscape-scale CO2 emissions of 0.2-1.1 g C/m**2/d during September 2008, of which 28-43% was from ponds and 27-46% from lakes. The lateral export of dissolved carbon was negligible compared to the gaseous emissions due to the small volumes of runoff. The concentrations of dissolved inorganic carbon in the ponds were found to triple during freezeback, highlighting their importance for temporary carbon storage between the time of carbon production and its emission as CO2. If ponds are ignored the total summer emissions of CO2-C from water bodies of the islands within the entire Lena Delta (0.7-1.3 Tg) are underestimated by between 35 and 62%.

Chemical and isotopic compositions of samples from the Haakon Mosby mud volcano and nearby

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active methane-bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanotrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (aver. d13C = -28.9 per mil) of CO2 produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (aver. d18O = 5 per mil) in carbonates is inherited from seawater sulfate. Rapid sulfate reduction (up to 12 mg S/dm**3/day) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this carbonates can only be formed in surface sediments near the water-bottom interface. Salinity as well as CO3/Ca and Mg/Ca ratios correspond to the field of non-magnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. Radiocarbon age of carbonates is about 10 Ka.

Oxygen and hydrogen isotopes measured in the Northeast Atlantic

Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 d18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, dD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0-100 m) and central (100-500 m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5 per mil for d18O and 0 to 2 per mil for dD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high d18O (0.5-1.1 per mil) and dD (3-6 per mil) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (d18O: -0.1 to 0.5 per mil; dD: -1 to 4 per mil) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed d18O-salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0.46 described previously by Pierre et al. (1994, J. Mar. Syst. 5 (2), 159-170.) for the tropical to subtropical Northeast Atlantic. This slope decreases to 0.46 for the subtropical North Atlantic Central Water (NACW) and the MOW and to 0.32 for the surface waters of the upper 50 m. The dD-salinity mixing lines have estimated slopes of 3.01 for the complete data, 1.26 for the MOW, 3.47 for the NACW, and 2.63 for the surface waters. The slopes of the d18O-dD relationship are significantly lower than the one for the Global Meteoric Water Line with 5.6 for the complete data set, 2.30 for the MOW, 4.79 for the NACW, and 3.99 for the surface waters. The lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics.

Molecular and isotopic properties of gases from ODP Holes of ODP Leg 204

We report and discuss molecular and isotopic properties of hydrate-bound gases from 55 samples and void gases from 494 samples collected during Ocean Drilling Program (ODP) Leg 204 at Hydrate Ridge offshore Oregon. Gas hydrates appear to crystallize in sediments from two end-member gas sources (deep allochthonous and in situ) as mixtures of different proportions. In an area of high gas flux at the Southern Summit of the ridge (Sites 1248-1250), shallow (0-40 m below the seafloor [mbsf]) gas hydrates are composed of mainly allochthonous mixed microbial and thermogenic methane and a small portion of thermogenic C2+ gases, which migrated vertically and laterally from as deep as 2- to 2.5-km depths. In contrast, deep (50-105 mbsf) gas hydrates at the Southern Summit (Sites 1248 and 1250) and on the flanks of the ridge (Sites 1244-1247) crystallize mainly from microbial methane and ethane generated dominantly in situ. A small contribution of allochthonous gas may also be present at sites where geologic and tectonic settings favor focused vertical gas migration from greater depth (e.g., Sites 1244 and 1245). Non-hydrocarbon gases such as CO2 and H2S are not abundant in sampled hydrates. The new gas geochemical data are inconsistent with earlier models suggesting that seafloor gas hydrates at Hydrate Ridge formed from gas derived from decomposition of deeper and older gas hydrates. Gas hydrate formation at the Southern Summit is explained by a model in which gas migrated from deep sediments, and perhaps was trapped by a gas hydrate seal at the base of the gas hydrate stability zone (GHSZ). Free gas migrated into the GHSZ when the overpressure in gas column exceeded sealing capacity of overlaying sediments, and precipitated as gas hydrate mainly within shallow sediments. The mushroom-like 3D shape of gas hydrate accumulation at the summit is possibly defined by the gas diffusion aureole surrounding the main migration conduit, the decrease of gas solubility in shallow sediment, and refocusing of gas by carbonate and gas hydrate seals near the seafloor to the crest of the local anticline structure.