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

About 150 basalt samples from Hole 504B, near the Costa Rica Rift were analyzed for sulfur content and sulfur-isotope composition. The basement in Hole 504B can be divided into an upper part, which has oxidative alteration (274.5-550 m below sea floor), and a lower part, which has nonoxidative alteration (550-835 m below sea floor) (the interval from 540 to 585 meters actually is transitional). This division is reflected in both the sulfur content and the sulfurisotope composition. Oxidative alteration of basalts by sea water at low temperatures has resulted in a depletion in sulfur in the upper part of the hole (mostly less than 600 ppm S) as compared to fresh sulfur-saturated oceanic tholeiites (900-1200 ppm S). High amounts of sulfur in the lower part of the hole are a result of precipitation of secondary pyrite under non-oxidative or weakly oxidative conditions from solutions which dissolved igneous sulfides. The average sulfur-isotope composition of the primary igneous sulfides is d34S = -0.01 per mil, which is close to the assumed mantle sulfur composition (d34S = 0 per mil. Pyrite and sulfate sulfur extracted together in a separate preparation step (as "pyrite-sulfate" sulfur) indicate addition of sea-water sulfate to the upper part of the basalts. The d34S of secondary pyrite isolated by hand-picking varies between -8.0 and +5.8 per mil; the "pyrite-sulfate" sulfur (d34S = -4.8 to +10.5 per mil), as well as that of the isolated pyrite, may have originated in the precipitation of pyrite from solutions containing sulfur from the dissolution of igneous sulfides, but addition of sulfur transported by hydrothermal solutions cannot be excluded.

Image analysis from TEM and AFM micrograph, Table S1, S2, S3, Figure S1, Figure S2

We report on metal enrichment along a natural pH gradient owing to increased CO2 degassing at cold, shal- low seeps of Vulcano Island in the Mediterranean Sea, off Sicily. We assessed composition of unfiltered and filtered seawater (b100 nm) along acidic zones ranging between ambient and pH 5, and showed that most seep derived elements are present as nanoclusters which then aggregate into larger colloids while mixing with ambient seawater along a pH gradient. Size and elemental composition of such naturally occurring nanoparticles assessed by modern characterisation methods were in good agreement with the results from conventional analytical methods. We provide analytical evidence for the presence in the water column of a large fraction of seep derived ele- ments (e.g. approximately 50% of iron, over 80% of Mn, 100% of Cr, S and Zn) in the form of nano sized par- ticles (e.g. b100 nm) even at typical open ocean pHs. We launch in situ sampling protocols and sample preparation procedures for multi-method suitable to obtain accurate measurements on nanoparticles from environmental samples. Based on our results a first insight to the formation of natural nanoparticles at cold CO2 seeps is presented and the persistence of such nano-clusters in the surrounding seawater is stipulated.

Acid-soluble sulfides in upper layer bottom sediments from the Tsemess and Gelendzhik bays and adjacent shelf area of the Black Sea

Contents of labile (acid-soluble) sulfides were determined in the upper layer of bottom sediments at 80 stations on the Caucasian shelf of the Black Sea. Maximum values of this parameter occurred in black mud accumulated in zones of intense pollution in the Gelendzhik and Tsemess bays and in shelf areas adjacent to large health resort objects and to seaports. Contents of acid-soluble sulfides in sediments varied from 400 to 900 mg S/dm**3 of wet mud. In zones of moderate pollution they varied from 200 to 400 mg S/dm**3. Rate of sulfate reduction was 10-40 mg S/dm**3 of wet sediment per day. Obtained data show that accumulation of labile sulfides in the upper layer of shelf bottom sediments is directly related to anthropogenic pollution and is one of the most hazardous environmental aftereffects.

Chemical composition of bottom sediments from the Discovery Deep, Red Sea rift zone

Hot brines in depressions of the central Red Sea contain thousands of times more iron, manganese and other metals than . After removal of salts, approximately half of sediments from these depressions consists of iron hydroxides and they are enriched in zinc, copper, lead and molybdenum. Hydrothermal deposits with the same complex of metals, located along the coast of the Red Sea, are correlated with faults and may be due to occurrences of Tertiary volcanism. Brines of similar composition are known in the Cheleken Peninsula. Certain geological and geochemical data indicate that such brines are of relatively deep origin.

Composition of Fe-Mn nodules and crusts from the Cape Basin

Facies zonation of the Cape basin with respect to Fe-Mn nodules based on data from Cruise 43 of R/V Akademik Kurchatov and published data is presented. Three facies regions are distinguished: the southern end of the Walvis Ridge and seamounts, the continental slope of the Southwest Africa and the deep-water Cape Basin. Iron-manganese nodules in the first of these areas are predominantly sedimentary, those in the second area are diagenetic and those in the third are sedimentary-diagenetic. Chemical characteristics and type of metallogenic specialization for each of the regions are identified.

Chemical composition of hydrothermal sulfide minerals from the Rainbow, Logachev-1, and Logachev-2 hydrothermal fields

Composition of ore minerals in MAR sulflde occurrences related to ultramaflc rocks was studied using methods of mineragraphy, electron microscopy, microprobe analysis, and X-ray analysis. Objects are located at various levels of maturity of sulflde mounds owing to differences in age, duration and degree of activity of the following hydrothermal systems: generally inactive Logatchev-1 field (up to 66.5 ka old), inactive Logatchev-2 field (3.9 ka), and generally active Rainbow field (up to 23 ka). Relative to MAR submarine ore occurrences in the basalt substrate, mineralization in the hydrothermal fields mentioned above is characterized by high contents of Au, Cd, Co, and Ni, along with presence of accessory minerals of Co and Ni. The studied mounds differ in quantitative ratios of major minerals and structural-textural features of ores that suggest their transformation. Ores in the Logatchev-1 field are characterized by the highest Cu content and development of a wide range of multistage contrast exsolution structures of isocubanite and bornite. In the Logatchev-2 field, sphalerite-chalcopyrite and gold-arsenic exsolution structures are present, but isocubanite exsolution structures are less diverse and contrast. The Rainbow field is marked by presence of homogenous isocubanite and the subordinate development of exsolution structures. The authors have identified four new phases in the Cu-Fe-S system. Phases X and Y (close to chalcopyrite and isocubanite, respectively) make up lamellae among isocubanite exsolution products in the Logatchev-1 and Logatchev-2 fields. Phase Y includes homogenous zones in zonal chimneys of the Rainbow field. Phases A and B formed in the orange bornite domain at low-temperature alteration of chalcopyrite in the Logatchev-1 field. Mineral assemblages of the Cu-S system are most abundant and diverse in the Logatchev-1 field, but their development is minimal in the Logatchev-2 field where mainly Cu-poor sulfides of the geerite-covellite series have been identified. Specific features of mineral assemblages mentioned above reflect the maturity grade of sulfide mounds and can serve as indicators of maturity.

Sulphur and iron species in Dvurechenskii mud volcano sediments

The deep Black Sea is known to be depleted in electron-acceptors for sulphide oxidation. This study on depth distributions of sulphur species (S(II), S(0),S(n)**2-,S2O3**2-,SO3**2-,SO4**2-) in the Dvurechenskii mud volcano, a cold seep situated in the permanently anoxic eastern Black Sea basin (Sorokin Trough, 2060 m water depth), showed remarkable concentrations of sulphide oxidation products. Sulphite concentrations of up to 11 µmol L**1-, thiosulphate concentrations of up to 22 µmol L**1-, zero-valent sulphur concentrations of up to 150 µmol L**1- and up to five polysulphide species were measured in the upper 20 cm of the sediment. Electron-acceptors found to be available in the Dvurechenskii mud volcano (DMV) for the oxidation of hydrogen sulphide to sulphide oxidation intermediates are iron-minerals, and probably also reactive manganese phases. Up to 60 µmol g**1- of reactive iron-minerals and up to 170 µmol L**1- dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow. Thus, the source for the oxidative power in the DMV are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments, leading to the formation of various sulphur intermediates in comparably high concentrations. Another possible source of sulphide oxidation intermediates in DMV sediments could be the formation of zero-valent sulphur by sulphate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero-valent sulphur. Sulphide oxidation intermediates, which are produced by these processes, do not reach thermodynamic equilibrium with rhombic sulphur, especially close to the active center of the DMV due to a short equilibration time. Thus, mud volcano sediments, such as in the DMV, can provide oxidizing niches even in a highly reduced environment like the abyssal part of the Black Sea.