(Table 1) K-Ar age and inert-gas-isotopes at DSDP Holes 68-501, 69-504B and 69-505B

Conventional K-Ar ages have been determined and inert-gas abundances have been measured on representative samples of altered rocks from Deep Sea Drilling Project Holes 501, 504B, and 505B in an attempt to correlate their degree of alteration with inert-gas and K-Ar data. Samples taken from the first 60 meters below the sediment/basalt interface give significantly higher ages than would be expected from the magnetic stratigraphy, though at greater depths the calculated ages are in broad agreement with the expected age. The inert gas ratios 20Ne/36Ar, 36Ar/84Kr, and 84Kr/130Xe also show a marked discontinuity at the 60-meter depth, and all these effects are interpreted as being a consequence of low-temperature alteration produced by burial metamorphism and by interaction with sea water (halmyrolysis).

(Table 1) Downhole variation of potassium, apparent K-Ar age, and inert gas abundances at DSDP Holes 69-504B, 70-504B and 83-504B

Ne, Ar, Kr, Xe, and K2O were measured in representative samples of holocrystalline basalt from DSDP Hole 504B. No hiatus in inert gas abundance is recognized at the base of the "oxic" alteration zone and the extent rather than the nature of alteration appears to determine these abundances. When the inert gas abundances are separately plotted against K2O, two distinct trends of loss emerge, one for alteration involving K-gain, the other for K-loss. Apparent whole-rock K-Ar ages are anomalous in the upper 50 m of basement, and below 300 m sub-basement. In the intervening zone of basement, celadonization adds sufficient potassium and eliminates enough "primary" 40Ar early in the history of the basalts for "excess" 40Ar to become subordinate to radiogenic 40Ar in basalts showing potassium enrichment greater than 0.2%. Stratigraphically correct K-Ar ages are obtained, therefore, from K-enriched basalts of the oxic alteration zone.

(Table 2) Geochemical composition of suspended matter samples from the northern Dvina River

The results of the analysis of samples of the Northern Dvina River's suspended particulate matter obtained by the sedimentation method from large water volumes in the periods of the spring high water and summer low water are presented. By the method of sequential leaching using different reagents, four fractions have been separated: the F1 is the sorbed complex and carbonates, the F2 is the amorphous hydroxides of Fe and Mn, the F3 is the form connected with the organic matter, and the F4 is the residual or silicate-detrital (inert) form. The data have shown that all ten elements determined were grouped with respect to the ratio of the distinguished forms: F4 is the predominant form for Al and Fe (73-88% of all the forms; however, the summer sample contains only 38% of this form of iron, and F2 is the predominant form for this period with 46.6%). As to Mn, the F1, F2, and F4 are nearly equally distributed in the spring high water samples, and only the F3 form is less important (5.4%). In the summer sample, the manganese sorbed complex is predominant (53.5%); for Cu, Ni, Cr, and Co, the inert F4 form is predominant (60-70%) in the sample of the spring suspended matter. The summer low water suspended matter has a lower F4 contribution (25-45%); for Zn, Pb, and Cd, the equal distribution of the forms in the spring samples is typical, while the summer suspended matter differs by the F2 form's predominance (53-61% for Zn and Pb). The main conclusion from the acquired data is that the geochemical mobility of all the studied elements, except for cadmium, in the summer low water suspended matter is higher than in the spring suspended matter. The more intensive biogeochemical processes in August, the high level of organic matter, and the higher contribution of phytoplankton lead to the intensification of the metals' geochemical activity in the Northern Dvina suspended matter in the end of the summer compared to the spring high water period when the physical processes are predominant over the biogeochemical ones due to the high speeds of the freshened waters flow.

(Table 1) Maceral composition and organic carbon chemistry of ODP Leg 104 samples

The Cenozoic sediments sampled in ODP Leg 104 on the Vøring Plateau show a distinct variability of the total organic carbon content (TOC) and the accumulation rates of TOC. Based on the geochemical and organic-petrographic characterization of the sedimentary organic matter (OM), the allochthonous and autochthonous proportion of the OM could be quantified. The results clearly demonstrate that high TOC percentages and TOC accumulation rates in Cenozoic sediment sections display a generally high input of allochthonous organic matter. Oxidized and partly well-rounded organic particles built up the main portion of OM within the Miocene, TOC-rich sediments. The most probable source of this oxidized OM are reworked sediments from the Scandinavian shelf. Changes in the input of these organic particles are to some degree correlative with sea-level changes. The Cenozoic accumulation of autochthonous OM is low and does not reveal a clear variation during the Miocene and early Pliocene. In spite of a high accumulation rate of biogenic opal during the Early Miocene, the accumulation rate of autochthonous TOC is low. The autochthonous particle assemblage is dominated by relatively inert OM, like dinoflagellate cysts. This points to an intensive biological and/or early diagenetic degradation of the marine OM under well oxidized bottom water conditions during the last 23 Myr. Nevertheless, a continuation of marine OM degradation during later stages of diagenesis cannot be excluded. A prominent dominance of allochthonous OM over autochthonous is documented with the beginning of the Pliocene. At 2.45 Ma the episodic occurrence of ice-rafted, thermally mature OM reflects the onset of the glacial erosion of Mesozoic, coal and black shale bearing sediments on the Scandinavian and Barents Sea shelves. The first occurrence of these, in view of the actual burial depth, thermally overmature OM particles is, therefore, a marker for the beginning of the strong Scandinavian glaciation and the advance of the glacial front toward the shelves.

Reflectance and composition of dispersed organic matter at DSDP Leg 67 Hole

Dispersed organic matter of plant origin from three sites of the Middle America Trench transect was investigated by coal petrographic methods. Samples from the slope region are rich in lipoid and inert substances. Humic matter is predominant in the trench sediments. Reflectance measurements show that the rank of the organic matter is peat, independent of the tectonic position and age of the samples in question. A slow increase of coalification with depth is observed.

Biomass and bioturbation in surface sediments of the Arctic Ocean

Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost three orders of magnitude from the shelf to the deep basins (e.g. 47 403 individuals m**-2 on the Chukchi Shelf to 95 individuals m**-2 in the Barents Abyssal Plain). Water depth is the primary determinant of infaunal density, explaining 39% of the total variability. Potential food concentration varies by almost two orders of magnitude during the late summer season (e.g. the phaeopigment concentration integrated to 10 cm varies from 36.16 mg m**-2 on the Chukchi Shelf to 0.94 mg m**-2 in the Siberia Abyssal Plain) but is not significantly correlated with density or biomass of the metazoa. Most stations show evidence of particle mixing, with mixing limited to <=3 cm below the sediment-water interface, and enhanced pore water irrigation occurs at seven of the nine stations examined. Particle mixing depths may be related to metazoan biomass, while enhanced pore water irrigation (beyond what is expected from diffusion alone) appears to be related to total phaeopigment concentration. The data presented here indicate that Arctic benthic ecosystems are quite variable, but all stations sampled contained infauna and most stations had indications of active processing of the sediment by the associated infauna.

Speciation of metals in bottom sediments from the south Kara Sea and Ob and Yenisei estuarine zones

Speciation of Fe, Mn, Zn, Cu, Co, Ni, Cr, Pb, and Cd was studied in 52 samples of bottom sediments collected during Cruise 49 of the R/V "Dmitry Mendeleev" to the estuaries of the Ob and Yenisei rivers and to the southwest Kara Sea. Immediately after sampling the samples were subjected to on-board consecutive extraction to separate metal species according to their modes of occurrence in the sediments: (1) adsorbed, (2) amorphous Fe-Mn hydroxides and related metals, (3) organic + sulfide, and (4) residual, or lithogenic. Atomic absorption spectroscopy of the extracts was carried out at a stationary laboratory. Distribution of Fe, Zn, Cu, Co, Ni, Cr, Pb, and Cd species is characterized by predominance of lithogenic or geochemically inert modes (70-95% of bulk contents), in which the metals are bound in terrigenous and clastic mineral particles and organic detritus. About half of total Mn amount and 15-30% of Zn and Cu are contained in geochemically mobile modes. Spatiotemporal variations in proportions of the metal species in the surface layer of sediments along sub-meridional sections and through vertical sections of bottom sediment cores testify that Mn and, to a lesser extent, Cu are the most sensitive to changes in sedimentation environment. The role of their geochemically mobile species notably increases under reducing conditions.

Composition of palagonitized basalts, their alteration products, and palagonitized basaltic glasses

Detailed petrochemical and geochemical studies of two samples of palagonitized basalts collected from depths 3060 and 4800 m have shown that palagonitization of tholeiitic basalt is accompanied by intensive removal of Ca and Mg and some removal of SiO2 from rocks. Appreciable amount of K is added to rocks in this process. Behavior of Fe, Al, Ti, Cr, and Na is inert. Palagonitization of alkalic basalt is accompanied by loss of SiO2, Ca, and Na from rocks. Contents of K and Mg are not changed. Four stages can be discerned in alteration of basalts under deep-sea conditions: syngenetic and diffusional palagonitization, hydrothermal leaching, and underwater weathering. Crusts of Fe-Mn ores are formed through removal of Fe, Mn, Ni, Co, Sn, and Mo from rocks and sorption of Pb, Hg, Yb, La, Bi, W, and Be from sea water.

Chemical composition and dated ages of detrital smectites in sediments at DSDP Legs 43, 48 and 50

Mineralogical, morphological and isotopic (Rb-Sr and K-Ar) determinations were made on some detrital smectites of Palaeocene and Cenomanian ages from DSDP. drillings in the Atlantic Ocean. These minerals are not inert in their depositional environment; authigenic laths grow on detrital sheets with sharp borders. This authigenesis could occur slightly after deposition in a closed system, for some of these smectites. It has been tentatively quantified by the Rb-Sr and K-Ar isotopic methods, which seem also well suited to evaluate the chemical extent of this authigenesis. At least, no preferential loss of 40Ar vs. 87Sr could be detected in the minerals, even in those which are smaller than 0.2 ?m.

Geochemistry, lithology and maceral analysis at DSDP Hole 71-511

The quantity, type, and maturity of the organic matter in Recent through Upper Jurassic sediments from the Falkland Plateau, DSDP Site 511, have been determined. Sediments were investigated for their hydrocarbon potential by organic carbon and Rock-Eval pyrolysis. Kerogen concentrates were prepared and analyzed in reflected and transmitted light to determine vitrinite reflectance and maceral content. Total extractable organic compounds were analyzed for their elemental composition, and the fraction of the nonaromatic hydrocarbons was determined by capillary column gas chromatography and combined gas chromatography/mass spectrometry. Three main classes of organic matter can be determined at DSDP Site 511 by a qualitative and quantitative evaluation of microscopic and geochemical results. The Upper Jurassic to lower Albian black shales contain high amounts of organic matter of dominantly marine origin. The content of terrigenous organic matter increases at the base of the black shales, whereas the shallowest black shales near the Aptian/Albian boundary are transitional in composition, with increasing amounts of inert, partly oxidized organic matter which is the dominant component in all Albian through Tertiary sediments investigated. The organic matter in the black shales has a low level of maturity and has not yet reached the onset of thermal hydrocarbon generation. This is demonstrated by the low amounts of total extractable organic compounds, low percentages of hydrocarbons, and the pattern and composition of nonaromatic hydrocarbons. The observed reflectance of huminite and vitrinite particles (between 0.4% and 0.5% Ro at bottom-hole depth of 632 m) is consistent with this interpretation. Several geochemical parameters indicate, however, a rapid increase in the maturation of organic matter with depth of burial. This appears to result from the relatively high heat flow observed at Site 511. If we relate the level of maturation of the black shales at the bottom of Hole 511 to their present shallow depth of burial, they appear rather mature. On the basis of comparisons with other sedimentary basins of a known geothermal history, a somewhat higher paleotemperature gradient and/or additional overburden are required to give the observed maturity at shallow depth. A comparison with contemporaneous sediments of DSDP Site 361, Cape Basin, which was the basin adjacent and to the north of the Falkland Plateau during the early stages of the South Atlantic Ocean, demonstrates differences in sedimentological features and in the nature of sedimentary organic matter. We interpret these differences to be the result of the different geological settings for Sites 361 and 511.

(Supplementary Table 1) Proportions of methane (C1) to ethane (C2) and the stable isotope composition of methane (d13CCH4) of gas and oil collected by gas bubble sampler during cruise M 114 in the southern Gulf of Mexico

Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1-2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.

(Table 2) Zinc complexation data from POLARSTERN cruise ANT-XXIV/3

The speciation of dissolved zinc (Zn) was investigated by voltammetry in the Atlantic sector of the Southern Ocean along two transects across the major frontal systems: along the Zero Meridian and across the Drake Passage. In the Southern Ocean south of the APF we found detectable labile inorganic Zn throughout the surface waters in contrast to studies from lower latitudes. Using a combination of ASV titrations and pseudopolarography revealed the presence of significant concentration of electrochemically inert Zn ligands throughout the Southern Ocean. These ligands however were nearly always saturated due to the presence of excess concentrations of dissolved Zn that were associated with the high nutrient waters south of the Antarctic Polar Front (APF). Only in surface waters did the concentration of Zn complexing ligands exceed the dissolved Zn concentrations suggesting a biological source for these ligands. Our findings have clear implications for the biogeochemical cycling of Zn and for the interpretation of paleo records utilizing Zn in opal as a tracer of Zn speciation in the water column.