Age determination of marine sediments in the western North Pacific by as partic acid chronology

The ages of fossil planktonic foraminifera,Pulleniatina obliquiloculata, in sediments (core 3bPC) from the western North Pacific were determined by aspartic acid chronology, which uses the racemization reaction rate constant of aspartic acid (k_Asp). Aspartic acid racemization-based ages (Asp ages) ranged from 7,600 yrBP at the surface, to 307,000 yrBP at a depth of 352.9 cm in the sediments. This sediment core was also dated by the glacial-interglacial fluctuation of δ¹⁸O chronology, and the ages determined by both chronologies were compared. The ages derived from aspartic acid chronology and δ¹⁸O stratigraphy were more or less consistent, but there appeared to be some differences in age estimates between these two dating methods at some depths within the core. In the core top sediments, the likely cause for the age discrepancy could be the loss of the surface sediment during sampling of the core. At depths of 66.3 and 139 cm within the core, Asp ages indicated reduced sedimentation rates duringca. 60,000-80,000 yrBP andca. 140,000–190,000 yrBP. The maximum age differences in both chronologies are 33,000 yr and 46,600 yr during each of these periods. These anomalous reductions in sedimentation rates occurring during these periods could possibly be related to some geological events, such as an increased dissolution effect of the calcium carbonate in the western North Pacific. Another possible reason for these age differences could be the unreliability in δ¹⁸O ages of core 3bPC as they were estimated by δ¹⁸O ages of another core, 3aPC.     

An automated precise Winkler titration for determining dissolved oxygen on board ship

An automated titration for the Winkler method is presented for measuring primary productivity in the ocean. The system is based on a microcomputer-controlled titration with potentiometric endpoint detection. By the use of 0.005-N sodium thiosulfate as a titrant and a program designed to shorten the time for measuring, the method achieves a precision of 0.04% coefficient of variation with a range of 0.01 to 0.10% for six replicates of samples at oxygen concentration of 70 to 250 M. It takes about four to five minutes to measure one sample.     

Using HED meteorites to interpret neutron and gamma‐ray data from asteroid 4 Vesta

Here, we construct a comprehensive howardite, eucrite, and diogenite (HED) bulk chemistry data set to compare with Dawn data. Using the bulk chemistry data set, we determine four gamma‐ray/neutron parameters in the HEDs (1) relative fast neutron counts (fast counts), (2) macroscopic thermal neutron absorption cross section (absorption), (3) a high‐energy gamma‐ray compositional parameter (C_p), and (4) Fe abundance. These correspond to the four measurements of Vesta made by Dawn's Gamma Ray and Neutron Detector (GRaND) that can be used to discern HED lithologic variability on the Vestan surface. We investigate covariance between fast counts and average atomic mass (<A>) in the meteorite data set, where a strong correlation (r² = 0.99) is observed, and we demonstrate that systematic offsets from the fast count/<A> trend are linked to changes in Fe and Ni concentrations. To compare the meteorite and GRaND data, we investigate and report covariance among fast counts, absorption, C_p, and Fe abundance in the HED meteorite data set. We identify several GRaND measurement spaces where the Yamato type B diogenites are distinct from all other HED lithologies, including polymict mixtures. The type B's are diogenites that are enriched in Fe + pigeonite + diopside ± plagioclase, relative to typical, orthopyroxenitic diogenites. We then compare these results to GRaND data and demonstrate that regions north of ~70°N latitude on Vesta (including the north pole) are consistent with type B diogenites. We propose two models to explain type B diogenite compositions in the north (1) deposition as Rheasilvia ejecta, or (2) type B plutons that were emplaced at shallow depths in the north polar region and sampled by local impacts. Lastly, using principal component (PC) analysis, we identify unique PC spaces for all HED lithologies, indicating that the corresponding GRaND measurables may be used to produce comprehensive lithologic maps for Vesta.     

Petromagnetic parameters of bottom sediments as indicators of the climatic and environmental changes in the central zone of the Sea of Okhotsk during the last 350 kyr

Bottom sediments from the central zone of the Sea of Okhotsk were preliminarily dated. The petromagnetic parameters of two groups of samples formed at cold and warm climatic stages were studied. Warm oxygen isotopic stages and substages were characterized by the coexistence of pseudo-single-domain allogenic magnetite and predominant magnetite and greigite (pyrrhotite) grains subject to biologic control. At cold stages, sediments containing a mixture of pseudo-single-domain and multidomain terrigenous magnetite particles accumulated. The petromagnetic curves agree with the normalized standard oxygen isotopic curve over the last 350 kyr of the column section.     

Silicon flux and distribution of biogenic silica in deep-sea sediments in the western North Pacific Ocean

We investigated biogenic silica, several biological components, and silicate in pore-water in the abyssal sediment to determine silicon flux of western North Pacific during several cruises. The surficial sediment biogenic silica content was high at high latitudes with the boundary running along the Kuroshio Extension, and maximum values (exceeding 20%) were found in the Oyashio region. In the subtropical region to the south, most stations showed less than 5% biogenic silica content. This distribution pattern reflected primary production and ocean currents in the surface layer very well. Pore-water samples were collected from 4 stations along the east coast of Japan. The highest asymptotic silicic acid concentration (670 μmol L^?1) in pore-water was observed at the junction of Kuroshio and Oyashio, followed by samples from the Oyashio region. It is at the southern station that the lowest value (450 μmol L^?1) was observed, and the primary production is low under the influence of Kuroshio there. The diffusive flux followed the same geographic trend as the asymptotic silicic acid concentrations did, ranging 77–389 mmol m^?2 yr ^?1. Multiple sampling of pore-water was conducted throughout the year at one station at high latitude. The average annual biogenic silica rain flux observed using sediment traps was 373 mmol m^?2 yr^?1; the diffusive flux and burial flux at the sediment–water interface were 305 and 9 mmol m^?2 yr^?1, respectively. We concluded that most of the settling silica particles dissolved and diffused at the sediment–water interface and approximately 3% only were preserved in this area. In addition, the obvious time lag observed between the peak rain flux and the maximum diffusive flux suggested that primary production in the surface layer has a great influence on the sedimentation environment of abyssal western North Pacific. These transitions of Si flux at the sediment–water interface were considerably greater in northwestern North Pacific than in southwestern North Pacific. In addition, a station in the Philippine Sea indicated high biogenic silica content because of Ethmodiscus ooze, which are scattered randomly on the sea floor in the subtropical region.     

Latitudinal Distribution of CO2 Fugacity along 175°E in the North Pacific in 1992–1996

In order to examine latitudinal distribution and seasonal change of the surface oceanic fCO₂, we analyzed the data obtained in the North Pacific along 175°E during the NOPACCS cruises in spring and summer of 1992–1996. Except for around the equator where the fCO₂ was significantly affected by the upwelling of deep water, the latitudinal distribution of fCO₂ showed distinctive seasonal variation. In the spring, the fCO₂ decreased and then increased going southward with the minimum value of about 300 µatm around 35°N, while in the summer, the fCO₂ displayed high variability, showing minimum and maximum values at latitudes of around 44° and 35°N, respectively. It was also found that the fCO₂ was well correlated with the SST, but the relationship between the two was different for different hydrographic regions. In the subpolar gyre, the frontal regions between the Water-Mass Front and the Kuroshio bifurcation front, and between the Kuroshio bifurcation front and the Kuroshio Extension current, SST, DIC and TA influenced the seasonal fCO₂ change through seasonally-dependent biological activities and vertical mixing and stratification of seawater. In the central subtropical gyre and the North Equatorial current, the seasonal fCO₂ change was found to be produced basically by changes in SST and DIC. The summertime oceanic fCO₂ generally increased with time over the period covered by this study, but the increased rate was clearly higher than those expected from other measurements in the western North Pacific.     

Continuing observation of disturbed reproductive cycle and ovarian spermatogenesis in the giant abalone, Haliotis madaka from an organotin-contaminated site of Japan

Histological examination of gonads as well as chemical analysis of organotin compounds in tissues of the giant abalone, Haliotis madaka, was conducted to evaluate continuing endocrine disruption in abalone populations in Japan. Abalone specimens were collected from two different areas, Tsushima as a reference site and Jogashima as a site representative of declining abalone populations where serious organotin contamination had been observed, each month from January 1998 to March 1999. Scores were given to the development stages of reproductive cells in the ovary and testis. The degree of sexual maturation was evaluated by calculating the mean value of a histogram of these scores for the reproductive cells of each abalone. The temporal variations in degree of sexual maturation showed that female and male abalone from Tsushima matured synchronously, while those from Jogashima did not, which were similar to results of the previous study during September 1995–November 1996. Approximately 19% of the female abalone from Jogashima were masculinized with an ovo-testis, which was also similar to the result of the previous study. The masculinization of female abalone is reported to be induced by tributyltin (TBT) and triphenyltin (TPhT) from antifouling paints. Concentrations of the sum of butyltins (TBT, dibutyltin (DBT) and monobutyltin (MBT): ΣBTs) and the sum of phenyltins (TPhT, diphenyltin (DPhT) and monophenyltin (MPhT): ΣPhTs) in the muscle of abalone from Jogashima (n = 73) of 7.8 ± 9.0 ng/g wet wt. and 4.5 ± 6.8 ng/g wet wt., respectively, were significantly higher than those from Tsushima (n = 87) of 4.7 ± 4.9 ng/g wet wt. and 0.8 ± 1.7 ng/g wet wt., respectively (p < 0.05 for ΣBTs; p < 0.001 for ΣPhTs), although concentrations of TBT and TPhT in the muscle of abalone from Jogashima (n = 73) of 2.2 ± 2.5 ng/g wet wt. and 5.8 ± 5.1 ng/g wet wt., respectively, were insignificantly and significantly higher than those from Tsushima (n = 87) of 0.4 ± 0.6 ng/g wet wt. and 0.5 ± 0.9 ng/g wet wt., respectively, (p > 0.05 for TBT; p < 0.001 for TPhT). Thus, endocrine disruption as well as contamination by organotins in the giant abalone from Jogashima is still persisting.     

Origin of the difference in the distribution behavior of tellurium and selenium in a soil-water system

The distribution behavior of tellurium (Te) between soil and water in a synthetic soil-water system was studied coupled with the speciation of Te both in soil and water phases by using X-ray absorption fine structure (XAFS) spectroscopy and a high-performance liquid chromatography connected to an ICP-MS (HPLC-ICP-MS), respectively. The results were compared with a similar data set for Se, which was simultaneously obtained in this study. The oxidation states and host phases of Te and Se in the soil samples were given by XAFS, while the oxidation states in water were given by HPLC-ICP-MS. It was found that both Te and Se in soil are mainly associated with Fe(III) hydroxides under oxic conditions. From the EXAFS analyses, the outer-sphere complex is important for the Se(VI) sorbed on Fe(III) hydroxides in soils, while Se(IV), Te(IV), and Te(VI) form inner-sphere complexes. Under reducing condition, it was found that Te(0) and Se(0) species were formed and that Se was more readily reduced to Se(0) than Te, as is predicted from their Eh-pH diagrams. The reduction process from hexavalent to zerovalent species was different between Se and Te, that is, the direct reduction from Se(VI) to Se(0) was observed for Se, while Te was reduced stepwise from Te(VI) to Te(0) via Te(IV). In terms of the distribution between soil and water, Se distribution to water was much higher than that of Te under wide redox conditions. For Se, selenate is the predominant species in water even under reducing condition due to the much higher solubility of Se(VI) than Se(IV). Furthermore, a much smaller distribution of Te in water was primarily due to the larger affinities of Te(IV) and Te(VI) to Fe(III) hydroxides than Se(VI), which originates from the formation of the inner-sphere complexes of Te(IV) and Te(VI) to Fe(III) hydroxides.