Component analysis of three TV-guided grab sampler from the Sahul Shelf (NW Australia)

This paper constitutes a first detailed and systematic facies and biota description of an isolated carbonate knoll (Pee Shoal) in the Timor Sea (Sahul Shelf, NW Australia). The steep and flat-topped knoll is characterized by a distinct facies zonation comprising (A) soft sediments with scattered debris and scarce sponges, hydrozoans and crinoids (320-210 m water depth), (B) hardground outcrops (step-like banks, vertical cliffs) that are mainly colonized by octocorals and sponges (210-75 m), and (C) the summit region (75-21 m) where the slopes merge gently into the flat-topped summit that is densely colonized by massive and encrusting zooxanthellate corals and the octocoral Heliopora coerulea. In contrast, the sediments recovered from the summit are dominated by the green alga Halimeda, subordinate components are corals, benthic foraminifers, mollusks, and coralline red algae. Thus, the sediments are classified as chlorozoan grain assemblage. However, non-skeletal grains (fecal pellets, ooids) are almost completely absent. This discrepancy between the living biota and the sediment composition could reflect a disruption by the severe tropical cyclone Ingrid that hit the northern Australian shelf in March 2005, just before the sampling for this study took place (September 2005).

(Table 4) Estimated surface water phosphate concentrations for the past 200 kyr at the location of sediment core GeoB1016-3

We compared ocean atlas values of surface water [PO4]3- and [CO2(aq)] against the carbon isotopic fractionation (ep) of alkenones obtained from surface sediments of the South Atlantic and the central Pacific (Pacific data are from Pagani et al. 2002, doi:10.1029/2002PA000756). We observed a positive correlation between ep and 1/[CO2(aq)], which is opposite of what would be expected if the concentration of CO2(aq) were the major factor controlling the carbon isotopic fractionation of C37:2 alkenones. Instead, we found inverse relationships between ep and [PO4]3- for the two ocean basins (for the Atlantic, ep = -4.6*[PO4]3- + 15.1, R = 0.76; for the Pacific, ep = -4.1*[PO4]3- + 13.7, R = 0.64), suggesting that ep is predominantly controlled by growth rate, which in turn is related to nutrient concentration. The similarity of the slopes implies that a general relationship between both parameters may exist. Using the relationship obtained from the South Atlantic, we estimated surface water nutrient concentrations for the past 200,000 years from a deep-sea sediment core recovered off Angola. Low ep values, indicating high nutrient concentrations, coincide with high contents of total organic carbon and C37 alkenones, low surface water temperatures, and decreased bulk d15N values, suggesting an increased upwelling of nutrient-rich cool subsurface waters as the main cause for the observed ep decrease.

Stable isotope record of Globorotalia inflata

We sampled the upper water column for living planktic foraminifera along the SW-African continental margin. The species Globorotalia inflata strongly dominates the foraminiferal assemblages with an overall relative abundance of 70-90%. The shell delta18O and delta13C values of G. inflata were measured and compared to the predicted oxygen isotope equilibrium values (delta18O(eq)) and to the carbon isotope composition of the total dissolved inorganic carbon (delta13C(DIC)) of seawater. The delta18O of G. inflata reflects the general gradient observed in the predicted delta18O(eq) profile, while the delta13C of G. inflata shows almost no variation with depth and the reflection of the delta13C(DIC) in the foraminiferal shell seems to be covered by other effects. We found that offsets between delta18O(shell) and predicted delta18O(eq) in the surface mixed layer do not correlate to changes in seawater [CO3[2-]]. To calculate an isotopic mass balance of depth integrated growth, we used the oxygen isotope composition of G. inflata to estimate the fraction of the total shell mass that is grown within each plankton tow depth interval of the upper 500 m of the water column. This approach allows us to calculate the DELTA delta13C(interval added-DIC); i.e. the isotopic composition of calcite that was grown within a given depth interval. Our results consistently show that the DELTA delta13C(IA-DIC) correlates negatively with in situ measured [CO3[2-]] of the ambient water. Using this approach, we found DELTA delta13C(IA-DIC)/[CO3[2-]] slopes for G. inflata in the large size fraction (250-355 µm) of -0.013 per mil to 0.015 per mil (µmol/kg)**-1 and of -0.013 per mil to 0.017 per mil (µmol/kg)**-1 for the smaller specimens (150-250 µm). These slopes are in the range of those found for other non-symbiotic species, such as Globigerina bulloides, from laboratory culture experiments. Since the DELTA delta13C(IA-DIC)/[CO3[2-]] slopes from our field data are nearly identical to the slopes established from laboratory culture experiments we assume that the influence of other effects, such as temperature, are negligibly small. If we correct the delta13C values of G. inflata for a carbonate ion effect, the delta13C(shell) and delta13C(DIC) are correlated with an average offset of 2.11.

Calcareous nannofossils of ODP Leg 101 holes

Leg 101 of the Ocean Drilling Program drilled 19 holes at 11 sites to investigate the geology of the Straits of Florida and the northern Bahamas. Drilling at Site 626 indicated that the Gulf Stream has had significant flow through the Straits of Florida for at least the last 24 million years. Winnowed, foraminiferal grainstones and packstones with sparse nannofossil assemblages and the reworking of older nannofossils suggest strong bottom-current activity throughout this interval. Drilling north of Little Bahama Bank and in Exuma Sound documents the growth of platform slopes during the late Cenozoic. Nannofossil biostratigraphy of the upper Cenozoic sediments from the Little Bahama Bank and Exuma Sound slope transects indicates relatively continuous deposition, with only short breaks in the periplatform ooze and/or calciturbidite accumulation during the late Pliocene. These unconformities may be linked to sea-level lowstands. Nannofossil assemblages are generally poorly preserved owing to accelerated diagenesis caused by high aragonite and high magnesium calcite contents of bank-derived material. High rates of influx of bank-derived materials appear to coincide with highstands of sea level. Periplatform sediments are largely limited to the upper Cenozoic at Little Bahama Bank. Pelagic and/or hemipelagic conditions existed during the Late Cretaceous and Paleogene. A relatively complete, continuous section of Oligocene is present in the Little Bahama Bank area, although the rest of the Paleogene is thin. Paleogene material is also present in Northeast Providence Channel, although its thickness is uncertain. A thick upper Campanian chalk sequence with abundant, moderately to well-preserved nannofossils occurs in the Little Bahama Bank area. Hemipelagic nannofossil marls and marly chalks at Little Bahama Bank contain an excellent nannofossil record, which indicates a continuous lowermost to middle Cenomanian sequence overlying the upper Albian drowned platform. These hemipelagic sediments are significantly younger than the organic-rich, middle Albian limestones in Northeast Providence Channel. The latter indicate that a deep-water channel was already well established by the middle Albian.

Analyses of Manganese nodules off Izu Island

Manganese nodules have been found by the author in the shallow waters of the Hyotan-se bank west of Shikime-jima, an island of the Izu archipelago in the Sea of Japan. The slopes around the bank are steep and rocks are exposed; gravels and coarse material cover the broad and flat plain on its top; andesite and basalt, which are very common in the bedrock, are found mingled with liparite gravels together with a number of manganese concretions from the bank.

Seawater carbonate chemistry and biological processes of coral Acropora muricata during experiments and observations in La Saline fringing reef, La Reunion Island, western Indian Ocean, 2011

The effect of decreasing aragonite saturation state (Omega Arag) of seawater (elevated pCO2) on calcification rates of Acropora muricata was studied using nubbins prepared from parent colonies located at two sites of La Saline reef (La Réunion Island, western Indian Ocean): a back-reef site (BR) affected by nutrient-enriched groundwater discharge (mainly nitrate), and a reef flat site (RF) with low terrigenous inputs. Protein and chlorophyll a content of the nubbins, as well as zooxanthellae abundance, were lower at RF than BR. Nubbins were incubated at ~27°C over 2 h under sunlight, in filtered seawater manipulated to get differing initial pCO2 (1,440-340 µatm), Omega Arag (1.4-4.0), and dissolved inorganic carbon (DIC) concentrations (2,100-1,850 µmol/kg). Increasing DIC concentrations at constant total alkalinity (AT) resulted in a decrease in Omega Arag and an increase in pCO2. AT at the beginning of the incubations was kept at a natural level of 2,193 ± 6 µmol/kg (mean ± SD). Net photosynthesis (NP) and calcification were calculated from changes in pH and AT during the incubations. Calcification decrease in response to doubling pCO2 relative to preindustrial level was 22% for RF nubbins. When normalized to surface area of the nubbins, (1) NP and calcification were higher at BR than RF, (2) NP increased in high pCO2 treatments at BR compared to low pCO2 treatments, and (3) calcification was not related to Omega Arag at BR. When normalized to NP, calcification was linearly related to Omega Arag at both sites, and the slopes of the relationships were not significantly different. The increase in NP at BR in the high pCO2 treatments may have increased calcification and thus masked the negative effect of low Omega Arag on calcification. Removing the effect of NP variations at BR showed that calcification declined in a similar manner with decreased Omega Arag (increased pCO2) whatever the nutrient loading.

Grains size and components distribution in turbidite layesr of ODP Leg 101

Textural and compositional differences were found between gravity-flow sheets in an open-ocean environment on the northern slope of Little Bahama Bank (Site 628, Pliocene turbidite sequence) and in a closed-basin depositional setting (Site 632, Quaternary turbidite sequence). Mud-supported debris-flow sheets were cored at Site 628. Average mean grain size of the turbidite samples was lower, mud content was higher, and sorting was poorer than in comparable samples from Site 632. This reflects the deposition of proximal, low-energy turbidity currents and debris flows on a base-ofslope carbonate apron. No mud-supported debris-flow sheets were deposited in the investigated sediment sequence of Hole 632A. Many larger turbidity currents from around the margins of Exuma Sound may have reached this central basin setting, depositing sediments that had been transported over longer distances. Planktonic components dominate in the grain-sized fraction (500-1000 µm) of turbidite samples from Hole 628A, while platform detritus is rare. We interpreted this as resulting from the erosion and reworking of a large area of open-ocean slope sediments by gravity flows. In contrast, large amounts of benthic and platform components were found in the turbidite samples of Hole 632A. This may be explained by the fact that the slopes of the enclosed Exuma Sound are steep, and turbidity currents bypassed much of these slopes through pronounced channels, delivering more shallow-water detritus to the deep basin. Erosion of slope sediments, a possible source area of planktonic detritus, is assumed to be low. The small slope area in relation to the larger surrounding platform areas and lower production of planktonic components in the enclosed waters of Exuma Sound may also explain the observed low number of planktonic components at Hole 632A. Turbidite material from both open-ocean and enclosed-basin environments was deposited at Site 635.

Compilation of d18O data, living planktic foraminifera

Most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate. To test these equations in the modern ocean, we measured the oxygen isotope composition of planktonic foraminifera (Globigerinoides ruber, Globigerinoides sacculifer, Globigerina bulloides and Neogloboquadrina pachyderma) collected from Atlantic and Southern Ocean surface waters, and added published plankton tow data from the Pacific, Indian and Arctic Oceans. The resulting species-specific regression equations of the temperature:d18O relationships for G. ruber, G. sacculifer and G. bulloides are statistically indistinguishable. The equations derived for G. sacculifer and G. bulloides agree with relationships obtained from laboratory experiments, in which these species were cultured at pH values close to modern surface waters. The equation derived from N. pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer Cibicides sp. Our work on plankton tow and pumped samples indicates that culture-derived equations appear to be more appropriate for predicting the absolute d18O of the species examined compared to equations derived from inorganic precipitates. However, over the oceanic temperature range, the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates.

Uranium and radioactive isotopes in bottom sediments and Fe-Mn nodules and crusts of seas and oceans

The main stages of the sedimentary cycle of uranium in modern marine basins are under consideration in the book. Annually about 18 thousand tons of dissolved and suspended uranium enters the ocean with river runoff. Depending on a type of a marine basin uranium accumulated either in sediments of deep-sea basins, or in sediments of continental shelves and slopes. In the surface layer of marine sediments hydrogenic uranium is predominantly bound with organic matter, and in ocean sediments also with iron, manganese and phosphorus. In diagenetic processes there occurs partial redistribution of uranium in sediments, as well as its concentration in iron-manganese, phosphate and carbonate nodules and biogenic phosphate detritus. Concentration of uranium in marine sediments of various types depending on their composition, as well as on forms of its entering, degree of differentiation and of sedimentation rates, on hydrochemical regime and water circulation, and on intensity of diagenetic processes.