Chemical composition and fluxes of deep sea suspended matter within and over the 9°50'N hydrothermal field, EPR

Results of geochemical studies of suspended matter from the water mass over the hydrothermal field at 9°50'N on the East Pacific Rise are reported. The suspended matter was sampled in background waters, in the buoyant plume, and in the near-bottom waters. Contents of Si, Al, P, Corg, Fe, Mn, Cu, Zn, Ni, Co, As, Cr, Cd, Pb, Ag, and Hg were determined. No definite correlations were found between the elements in the background waters. Many of the chemical elements correlated with Fe and associated with its oxyhydroxides in the buoyant plume. In the near-bottom waters trace elements are associated with Fe, Zn, and Cu (probably, with their sulfides formed during mixing of hydrothermal fluids with seawater). Chemical composition of sediment matter precipitated in a sediment trap was similar to the near-bottom suspended matter.

Contents of radioactive elements, main chemical composition, and sedimentation rates of bottom sediments from some stations in the Southeast Pacific

Gamma-spectrometric analysis was used for six sediment cores from the area occupied by metalliferous sediments in the Southeast Pacific. In five of these cores vertical distribution curves of 230Th enabled positions of equilibrium points to be determined and sediments to be dated. The ionium curve was normalized for one core. Vertical distribution of 230Th in metalliferous sediments resembles its distribution in normal ocean-floor sediments beyond the area of influence of active ridges. Sedimentation rates lay within the range 0.7-12.3 mm/ky.

Geochemical composition and crystallization conditions of melts from the Mid Atlantic Ridge near Ascension Island (7-11°S)

Phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the Mid-Atlantic Ridge (MAR) east of Ascension Island (7°11°S).The results indicate that midocean ridge basalt (MORB) magmas beneath different segments of the MAR have crystallized over a wide range of pressures (100-900MPa). However, each segment seems to have a specific crystallization history. Nearly isobaric crystallization conditions (100-300MPa) were obtained for the geochemically enriched MORB magmas of the central segments, whereas normal (N)-MORB magmas of the bounding segments are characterized by polybaric crystallization conditions (200-900MPa). In addition, our results demonstrate close to anhydrous crystallization conditions of N-MORBs, whereas geochemically enriched MORBs were successfully modeled in the presence of 0.4-1wt% H2O in the parental melts.These estimates are in agreement with direct (Fourier transform IR) measurements of H2O abundances in basaltic glasses and melt inclusions for selected samples. Water contents determined in the parental melts are in the range 0.04-0.09 and 0.30-0.55 wt% H2O for depleted and enriched MORBs, respectively. Our results are in general agreement (within ±200MPa) with previous approaches used to evaluate pressure estimates in MORB. However, the determination of pre-eruptive conditions of MORBs, including temperature and water content in addition to pressure, requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water. KEY WORDS: MORB; Mid-Atlantic Ridge; depth of crystallization; water abundances; phase equilibria calculations; cotectic crystallization; pressure estimates; polybaric fractionation

Effects of pCO2 and iron on the elemental composition and cell geometry of the marine diatom Pseudo-nitzschia pseudodelicatissima//(Bacillariophyceae)

Partial pressure of CO2 (pCO2) and iron availability in seawater show corresponding changes due to biological and anthropogenic activities. The simultaneous change in these factors precludes an understanding of their independent effects on the ecophysiology of phytoplankton. In addition, there is a lack of data regarding the interactive effects of these factors on phytoplankton cellular stoichiometry, which is a key driving factor for the biogeochemical cycling of oceanic nutrients. Here, we investigated the effects of pCO2 and iron availability on the elemental composition (C, N, P, and Si) of the diatom Pseudo-nitzschia pseudodelicatissima (Hasle) Hasle by dilute batch cultures under 4 pCO2 (~200, ~380, ~600, and ~800 µatm) and five dissolved inorganic iron (Fe'; ~5, ~10, ~20, ~50, and ~100 pmol /L) conditions. Our experimental procedure successfully overcame the problems associated with simultaneous changes in pCO2 and Fe' by independently manipulating carbonate chemistry and iron speciation, which allowed us to evaluate the individual effects of pCO2 and iron availability. We found that the C:N ratio decreased significantly only with an increase in Fe', whereas the C:P ratio increased significantly only with an increase in pCO2. Both Si:C and Si:N ratios decreased with increasing pCO2 and Fe'. Our results indicate that changes in pCO2 and iron availability could influence the biogeochemical cycling of nutrients in future oceans with high- CO2 levels, and, similarly, during the time course of phytoplankton blooms. Moreover, pCO2 and iron availability may also have affected oceanic nutrient biogeochemistry in the past, as these conditions have changed markedly over the Earth's history.

Accumulation rates, carbon composition and Eocene carbonate compensation depths of ODP Sites 199-1218 and 199-1219

CaCO3, Corg, and biogenic SiO2 were measured in Eocene equatorial Pacific sediments from Sites 1218 and 1219, and bulk oxygen and carbon isotopes were measured on selected intervals from Site 1219. These data delineate a series of CaCO3 events that first appeared at ~48 Ma and continued to the Eocene/Oligocene boundary. Each event lasted 1-2 m.y. and is separated from the next by a low CaCO3 interval of a similar time span. The largest of these carbonate accumulation events (CAE-3) is in Magnetochron 18. It began at ~42.2 Ma, lasted until ~40.3 Ma, and was marked by higher than average productivity. The end of CAE-3 was abrupt and was associated with a large-scale carbon transfer to the oceans prior to warming of high-latitude regions. Changes in carbonate compensation depth associated with CAE excursions were small in the early part of the middle Eocene but increased to as much as 800 m by the late middle Eocene before decreasing into the late Eocene. Oxygen isotope data indicate that the carbonate events are associated with cooling conditions and may mark small glaciations in the Eocene.

Temperature Dependent Effects of Elevated CO2 on Shell Composition and Mechanical Properties of Hydroides elegans: Insights from a Multiple Stressor Experiment

The majority of marine benthic invertebrates protect themselves from predators by producing calcareous tubes or shells that have remarkable mechanical strength. An elevation of CO2 or a decrease in pH in the environment can reduce intracellular pH at the site of calcification and thus interfere with animal's ability to accrete CaCO3. In nature, decreased pH in combination with stressors associated with climate change may result in the animal producing severely damaged and mechanically weak tubes. This study investigated how the interaction of environmental drivers affects production of calcareous tubes by the serpulid tubeworm, Hydroides elegans. In a factorial manipulative experiment, we analyzed the effects of pH (8.1 and 7.8), salinity (34 and 27), and temperature (23°C and 29°C) on the biomineral composition, ultrastructure and mechanical properties of the tubes. At an elevated temperature of 29°C, the tube calcite/aragonite ratio and Mg/Ca ratio were both increased, the Sr/Ca ratio was decreased, and the amorphous CaCO3 content was reduced. Notably, at elevated temperature with decreased pH and reduced salinity, the constructed tubes had a more compact ultrastructure with enhanced hardness and elasticity compared to decreased pH at ambient temperature. Thus, elevated temperature rescued the decreased pH-induced tube impairments. This indicates that tubeworms are likely to thrive in early subtropical summer climate. In the context of climate change, tubeworms could be resilient to the projected near-future decreased pH or salinity as long as surface seawater temperature rise at least by 4°C.

Organic carbon and humic substances contents, carbon isotope composition and peroxidase activity in sediments from DSDP Sites 15-147 and 75-532

Sediment samples from the Cariaco Trench (DSDP Leg 15) and the Walvis Ridge (DSDP Leg 75) ranging in age from Holocene to Upper Miocene (approximately 8 million years BP) and in depth from 5 to 258 m were extracted with basic sodium pyrophosphate and the extract analyzed for enzymic activity. Since no dehydrogenase, alkaline phosphatase or esterase activity was found, it is estimated from these data that the maximum bacterial population does not exceed 1000 cells per gram dry sediment. Peroxidase activity was, however, found in most samples: this showed marked dependence on the humic substance concentration (expressed as percent of the organic carbon content) and increased with depth at a rate of 33 units per meter. To explain this observation, we favor an hypothesis based on the presence of active humic-enzyme association. The humic substances absorb and stabilize peroxidase which is liberated throughout the sediment column by lysis of cells. The association of the enzyme with the humic substances protects it from biodegradation and denaturation. This hypothesis agrees with laboratory experiments which show the enhanced stability of humic-enzyme complexes towards degradation by biological, chemical and thermal effects.

Phytoplankton composition and biomass during leg 7 of Galathea 3 cruise across the southern Indian Ocean

Phytoplankton composition and biomass was investigated across the southern Indian Ocean. Phytoplankton composition was determined from pigment analysis with subsequent calculations of group contributions to total chlorophyll a (Chl a) using CHEMTAX and, in addition, by examination in the microscope. The different plankton communities detected reflected the different water masses along a transect from Cape Town, South Africa, to Broome, Australia. The first station was influenced by the Agulhas Current with a very deep mixed surface layer. Based on pigment analysis this station was dominated by haptophytes, pelagophytes, cyanobacteria, and prasinophytes. Sub-Antarctic waters of the Southern Ocean were encountered at the next station, where new nutrients were intruded to the surface layer and the total Chl a concentration reached high concentrations of 1.7 µg Chl a/L with increased proportions of diatoms and dinoflagellates. The third station was also influenced by Southern Ocean waters, but located in a transition area on the boundary to subtropical water. Prochlorophytes appeared in the samples and Chl a was low, i.e., 0.3 µg/L in the surface with prevalence of haptophytes, pelagophytes, and cyanobacteria. The next two stations were located in the subtropical gyre with little mixing and general oligotrophic conditions where prochlorophytes, haptophytes and pelagophytes dominated. The last two stations were located in tropical waters influenced by down-welling of the Leeuwin Current and particularly prochlorophytes dominated at these two stations, but also pelagophytes, haptophytes and cyanobacteria were abundant. Haptophytes Type 6 (sensu Zapata et al., 2004), most likely Emiliania huxleyi, and pelagophytes were the dominating eucaryotes in the southern Indian Ocean. Prochlorophytes dominated in the subtrophic and oligotrophic eastern Indian Ocean where Chl a was low, i.e., 0.043-0.086 µg total Chl a/L in the surface, and up to 0.4 µg Chl a/L at deep Chl a maximum. From the pigment analyses it was found that the dinoflagellates of unknown trophy enumerated in the microscope at the oligotrophic stations were possibly heterotrophic or mixotrophic. Presence of zeaxanthin containing heterotrophic bacteria may have increased the abundance of cyanobacteria determined by CHEMTAX.

Composition and age of igneous rocks from the Vityaz Ridge

Results of geological research carried out by V.I. Il'ichev Pacific Oceanological Institute (Far East Division of the Russian Academy of Sciences) and P.P. Shirshov Institute of Oceanology (Russian Academy of Sciences) on the submarine Vityaz Ridge during Cruise 37 of R/V Akademik Lavrentyev in 2005 are discussed. Various rocks composing the basement and the sedimentary cover of the ridge were dredged in three areas. Based on isotope geochronology, petrogeochemical, petrographic, and paleontological data and comparison with similar rocks available from the adjacent land and the Sea of Okhotsk, they are subdivided into several age complexes. Late Cretaceous, Eocene, Late Oligocene, Miocene, and Pliocene-Pleistocene complexes are defined among igneous rocks, while volcanogenic-sedimentary rocks are united into Late Cretaceous - Early Paleocene (Late Campanian - Danian), undivided Paleogene (Paleocene-Eocene?), Oligocene - Early Miocene, and Pliocene-Pleistocene complexes. Obtained data on age and formation settings of the defined complexes allowed to reconstruct geological evolution of the central Pacific slope of the Kurile Island arc.