Biomass of picophytoplankton in the Black Sea in winter 1991

Studies of picophytoplankton were carried out in the open Black Sea from February to April 1991 with concomitant blooming of diatoms. During this period cyanobacteria predominated in picoplankton averaging 98.8% of total picophytoplankton abundance and 95% of total picoplankton biomass. In February number of cells reached 1.5x10**9 per liter in the East Black Sea. Picoplankton biomass decreased during the observation period. From February to March biomass varied from 452 to 4918 mg/m**2 (av. 1632 mg/m**2), and from March through April from 4 to 656 mg/m**2 (av. 190 mg/m**2). Vertical distribution of picoplankton was determined by the upper margin of the main pycnocline. The major part of picoplankton biomass occurred in the mixed layer. With appearance of seasonal pycnoclines in the last days of March maximum biomass occurred under the upper mixed layer. No relationship was observed between Nitzschia delicatula bloom and picoplankton.

Mineralogy and geochemistry of latest Miocene deposits in the Tyrrhenian Sea

Late Miocene sediments from ODP Sites 652 and 654, drilled on the Sardinian margin in the Western Tyrrhenian Sea, are investigated through mineralogical, micromorphological, geochemical, and microgeochemical analyses. Clay associations appear to be little controlled by conditions of deposition, and largely depend on pre- and post-depositional conditions. The sedimentary series from Central Mediterranean gives very different geodynamic information, according to the sector considered. While relatively stable conditions, like those encountered in Caltanissetta Basin, Sicily, favor the mineralogical expression of warm-temperate and subarid Messinian climate, the Eastern Sardinia margin (Site 654) clay suites mainly reflect the transition from tectonically active to relaxed conditions. The series deposited at the foot of the same margin above a thinner crust (Site 652) experienced the effects of burial diagenesis, enhanced by strong geothermal gradient.

Secondary minerals and geochemistry in basalts at DSDP Leg 67 Legs

Secondary minerals in basalts from Holes 495 and 500 include smectite and chlorite, both of which have partially replaced the basalt groundmass. In addition to these two minerals, amphibole, laumontite, albite, and a corrensitelike mineral are present in Holes 499B and 499C. Smectite, chlorite, talc, calcite, phillipsite, mica, and mixed-layer chlorite-montmorillonite also fill veins in the basalts of Hole 495. The secondary mineral assemblages from Site 499 are characteristic of the initial stage of greenschist facies metamorphism.

Composition of Fe-Mn nodules and crusts from the Southwest Pacific

A study of samples dredged within areas of tectonic arc-trench systems (Kermadec and New Hebrides) allows to distinguish three types of ferromanganese mineralization. Relationship between mineral and geochemical specialization is established. A conclusion is made that ferromanganese mineralization is a permanent genetic series of matter supply: from endogenic (hydrothermal solution is a dominant source at deposition of chemical elements from mixture seawater plus hydrothermal solutions) to hydrogenic (seawater is a dominant source at element deposition). This results in geochemical and mineralogical variety of ferromanganese mineralization within this part of the Pacific Ocean.

Pleistocene stable isotope record of planktonic foraminifera of ODP Site 138-847

We present Pleistocene oxygen and carbon isotope records from two planktonic foraminifer species (Globigerinoides sacculifer and Neogloboquadrina dutertrei) from Ocean Drilling Program Site 847 (0°16'N, 95°19'W; 3334 m water depth). An average sample resolution of 4500 yr was obtained by sampling at an interval of 15 cm through a continuous 35-m section from 0 to 1.15 Ma. Our d18O-based chronology is similar to that derived independently by astronomically tuning the gamma-ray attenuation porosity evaluator (GRAPE) record (Shackleton et al., 1995), though offsets as large as ± 30 k.y. occur on occasion. The surface waters at eastern equatorial Pacific Site 847, 380 km west of the Galapagos, are characterized by strong and constant upwelling, elevated nutrient concentrations, and high productivity. The isotopic composition of G. sacculifer (300-355 µm) reflects conditions in the thin-surface mixed layer, and the composition of N. dutertrei (355-425 µm) monitors the subsurface waters of the permanent shallow (10-40 m) thermocline. The Pleistocene d18O difference (N. dutertrei minus G. sacculifer, Dd18Od-s) averages 0.9 per mil and ranges from 0 per mil to 1.7 per mil. Neglecting species effects and shell size, the average Pleistocene d13C difference (G. sacculifer minus N. dutertrei, Dd13Cs-d) is 0.0 per mil and ranges from -0.5 per mil to 0.5 per mil. The Dd18Od-s and Dd13Cs-d records are used to infer vertical contrasts in upper ocean water temperature and nutrient concentration, though d13C may also be influenced by other factors, such as CO2 gas exchange. Variations in the isotopic differences are often synchronous with glacial/interglacial climate change. Glacial periods are characterized by smaller vertical contrasts in both temperature and nutrient concentration, and by notably greater accumulation rates of N. dutertrei and CaCO3. We attribute these responses to greater upwelling at the equatorial divergence. Superimposed on the glacial/interglacial Dd18Od-s pattern is a long-term trend possibly associated with the advection of Peru Current waters. The temporal fluctuations in the isotopic contrasts are strikingly similar to those observed at Site 851 (Ravelo and Shackleton, this volume), suggesting that the inferred changes in thermal and chemical profiles occurred over a broad region in the equatorial Pacific.

Global Ocean Biomes: Mean and time-varying maps (NetCDF 7.8 MB)

Large-scale studies of ocean biogeochemistry and carbon cycling have often partitioned the ocean into regions along lines of latitude and longitude despite the fact that spatially more complex boundaries would be closer to the true biogeography of the ocean. Herein, we define 17 open-ocean biomes classified from four observational data sets: sea surface temperature (SST), spring/summer chlorophyll a concentrations (Chl a), ice fraction, and maximum mixed layer depth (maxMLD) on a 1° × 1° grid. By considering interannual variability for each input, we create dynamic ocean biome boundaries that shift annually between 1998 and 2010. Additionally we create a core biome map, which includes only the grid cells that do not change biome assignment across the 13 years of the time-varying biomes. These biomes can be used in future studies to distinguish large-scale ocean regions based on biogeochemical function.

Physical properties and bulk minerals from IODP Holes 308-U1322B, U1322D and U1324B

How the micro-scale fabric of clay-rich mudstone evolves during consolidation in early burial is critical to how they are interpreted in the deeper portions of sedimentary basins. Core samples from the Integrated Ocean Drilling Program Expedition 308, Ursa Basin, Gulf of Mexico, covering seafloor to 600 meters below sea floor (mbsf) are ideal for studying the micro-scale fabric of mudstones. Mudstones of consistent composition and grain size decrease in porosity from 80% at the seafloor to 37% at 600 mbsf. Argon-ion milling produces flat surfaces to image this pore evolution over a vertical effective stress range of 0.25 (71 mbsf) to 4.05 MPa (597 mbsf). With increasing burial, pores become elongated, mean pore size decreases, and there is preferential loss of the largest pores. There is a small increase in clay mineral preferred orientation as recorded by high resolution X-ray goniometry with burial.

Secondary minerals and geochemistry at DSDP Legs 68 and 69

Basalt samples recovered during DSDP Legs 68, 69, and 70 from a 550-meter-thick section in two holes near the Costa Rica Rift (Holes 501 and 504B) were found to contain the following secondary minerals: trioctahedral and dioctahedral smectite, chlorite, mixed-layer clays, talc, hematite, pyrite, foujasite, phillipsite, analcime, natrolite, thomsonite, gyrolite, aragonite, calcite, anhydrite, chalcocite, Fe-hydrosilicate, okenite, apophyllite, actinolite, cristobalite, quartz, and magnesite. A less positive identification of bismutite was made. A mineral rich in Mn and minerals with strong reflections at 12.9 Å and 3.20 Å remain unidentified. Trioctahedral smectite replaces glass and olivine in the basalt groundmass. The other secondary minerals occur in veins. The distribution of the secondary minerals in the basalt section shows both hydrothermal and oxidizing-nonoxidizing zonation. Most of the secondary minerals formed under alkaline, nonoxidizing conditions at temperatures up to 120° C. An acidic regime probably existed in the lowest portion of basalt. Oxidative diagenesis followed nonoxidative diagenesis in the upper part of the section. Oxidative diagenesis is characterized by the absence of celadonite, rare occurrences of dioctahedral smectite, and widespread hematite and phillipsite.