Strontium and neodymium concentrations and isotope compositions in fossil fish teeth and pore waters at ODP Sites 130-807 and 125-786

We analyzed Nd and Sr isotopic compositions of Neogene fossil fish teeth from two sites in the Pacific in order to determine the effect of cleaning protocols and burial diagenesis on the preservation of seawater isotopic values. Sr is incorporated into the teeth at the time of growth; thus Sr isotopes are potentially valuable for chemostratigraphy. Nd isotopes are potential conservative tracers of paleocirculation; however, Nd is incorporated post-mortem, and may record diagenetic pore waters rather than seawater. We evaluated samples from two sites (Site 807A, Ontong Java Plateau and Site 786A, Izu-Bonin Arc) that were exposed to similar bottom waters, but have distinct lithologies and pore water chemistries. The Sr isotopic values of the fish teeth appear to accurately reflect contemporaneous seawater at both sites. The excellent correlation between the Nd isotopic values of teeth from the two sites suggests that the Nd is incorporated while the teeth are in chemical equilibrium with seawater, and that the signal is preserved over geologic timescales and subsequent burial. These data also corroborate paleoseawater Nd isotopic compositions derived from Pacific ferromanganese crusts that were recovered from similar water depths (Ling et al., 1997; doi:10.1016/S0012-821X(96)00224-5). This corroboration strongly suggests that both materials preserve seawater Nd isotope values. Variations in Pacific deepwater e-Nd values are consistent with predictions for the shoaling of the Isthmus of Panama and the subsequent initiation of nonradiogenic North Atlantic Deep Water that entered the Pacific via the Antarctic Circumpolar Current.

Isotopic composition of bottom and interstitial waters in the area of gas plumes, Sea of Okhotsk

Data on isotopic composition of interstitial and bottom waters collected in an area of gas hydrate occurrence in the Sea of Okhotsk are presented. Investigations indicate that heavy isotopes of oxygen and hydrogen are used in generation of gas hydrate, so that isotopic composition of its water of constitution is: d18O = +1.9 per mil, d2H = +23 per mil (relative to SMOW). Production of authigenic carbonates results in isotopic exchange with interstitial water, which in turn alters its isotopic composition by an increase in d18O. Bottom waters are isotopically light relative to the SMOW standard and to the average isotopic composition of interstitial waters in the area of gas hydrate occurrence in study.

Dominance of facultative and obligate oligotrophic bacteria in surface waters above Gunnerus and Astrid Ridge, Antarctic Ocean

Facultative and obligate oligotrophs have been enumerated in March/April 1990 by the MPN-method with 14C-protein hydrolysate as tracer substrate. Obligate (10-3360 cells/ml) and facultative (110-9000 cells/ml) oligotrophs revealed to be the dominant population above Gunnerus Ridge (65°30'-68°S; 31-35°E) at a depth of 25 m compared with eutrophic bacteria (5 to 260 CFU/ml). Above Astrid Ridge (65-68°S; 8-18°E), obligate (0-1100 cells/ml) and facultative oligotrophs (300-9000 cells/ml) were also abundant but not always dominant. Bacterial biomass above Gunnerus Ridge was only between 7.3 and 43.6% of particulate biomass, but biomass of bacteria above Astrid Ridge amounted from 56.9 to >100% of particulate biomass; an exception was station no. PS16/552 with only 22.2% of bacterial biomass. Ratio of bacterial biomass to particulate biomass was negatively correlated with maximal primary production, complementing the view that phytoplankton was the dominant population above Gunnerus Ridge, whereas bacteria predominated above Astrid Ridge. Eutrophic bacteria were also more abundant above Astrid Ridge, with 3 to 6380 CFU/ml. Total bacteria by acridine orange direct counts amounted from 1 x 10**4 to 34.2 x 10**4 cells/ml. Bacterial biomass above Gunnerus Ridge was 1.8 to 10.7, and above Astrid Ridge 5.7 to 13.6 mg C/m*3. Maximal primary production above Gunnerus Ridge was 4.5 to 11.0, and above Astrid Ridge 2.3 to 3.5 mg C/m**3/d.

Geochemistry and mineralogy of interstitial waters and clays in sediments of ODP Leg 180 sites

Oxygen and strontium isotopes and Rb and Ba were determined in interstitial water (IW) collected from Sites 1109, 1115, and 1118 drilled on the Woodlark Rise during Ocean Drilling Program Leg 180. The trace element and mineralogical composition of the clay fraction of sediments isolated from the squeeze cakes corresponding to IW samples from Site 1109 was also determined.

Carbon isotopic composition and dissolved CO2 concentration in pore waters of ODP Leg 174A sites

Microbially mediated redox diagenetic processes in marine sediments are reflected in the amount and carbon isotopic composition of dissolved CO2 and CH4 (Claypool and Kaplan, 1974). Oxidation of organic matter gives rise to dissolved CO2 with about the same 13C/12C ratio as the starting organic matter. Subsequent reduction of CO2 to form CH4 involves a large (~70) kinetic isotopic effect, resulting in significant 13C depletion in the CH4, and 13C enrichment in the residual CO2. Ocean Drilling Program Leg 174A (offshore New Jersey) presented an opportunity to study these processes in shelf and upper slope sediments. Holes 1071A-1071D, 1071F, and 1072A were drilled on the shelf in water depths of 88.0-98.1 m. Hole 1073A was drilled on the slope in 639.4 m of water. Pore-water samples were collected for analysis at all three sites, whereas gas samples could only be obtained from Hole 1073A on the slope.

Abundance and biomass of bacterioplankton in waters of the Kara Sea and the Ob and Yenisey Rivers

Bacterial cell number in the water column of the Kara Sea and estuary areas of the Ob and Yenisey Rivers was determined in water samples collected at 32 stations at depths from the surface to 200 m. The samples were analyzed by direct microscopy. In most parts of the sea microorganism concentrations ranged generally from 103 to 104 cells per ml and their biomasses from milligrams to tens of mg/m**3. Bacterioplankton concentration of river waters was much higher than in the open sea, especially in Ob waters. The highest bacteria concentrations, hundreds of thousands cells per ml with biomass exceeding 200 mg/m**3, were found in the southern part of the Ob section. Minimal concentrations were observed in the northeastern part and near the southeastern part of the Ob section and the southeastern coast of Novaya Zemlya. Dark CO2 fixation rates determined at some stations indicated low bacteria biomass production.

Strontium isotopic composition of interstitial waters from DSDP sites 25-245 and 38-336

Measurements of 87Sr/86Sr ratios of interstitial waters from leg 25, site 245 and leg 38, site 336 of the Deep Sea Drilling Project show that the enrichment of Sr[2+] with depth is caused both by the alteration of volcanic material and by the introduction of strontium derived from calcium carbonate. 87Sr/86 Sr ratios range from 0.70913 to 0.70794 at site 245 and from 0.70916 to 0.70694 at site 336. The low ratios compared with contemporaneous seawater reflect the release of Sr from a volcanic source having, according to material-balance calculations, a 87Sr/86 Sr ratio of about 0.7034 at site 336. At this site the source appears to be volcanic ash and not basaltic basement which acts as a sink for Sr[2+] during in situ low-temperature weathering. The volcanic contribution to the strontium enrichment in the basal interstitial waters varies from <10% at site 245 to >50% at site 336. The remaining Sr[2+] is derived from Sr-rich biogenic carbonate during diagenetic recrystallization to form Sr-poor calcite.