Masahiro Maruo

Distribution of trace bioelements in the subarctic North Pacific Ocean and the Bering Sea (the R/V Hakuho Maru Cruise KH-97-2)

A column concentration-high resolution inductively coupled plasma mass spectrometry (ICP-MS) determination was applied to measure the total dissolved concentrations of Fe, Co, Ni, Cu and Zn in seawater collected from the subarctic North Pacific (~45°N) and the Bering Sea in July–September 1997. Total adsorbable Mn was determined on board by column electrolysis preconcentration and chemiluminescence detection. The vertical profiles for Fe, Ni and Zn were nutrient-like. The deep water concentration of Fe was ~0.5 nM in the northeast Pacific (18°-140°W) and increased to ~1 nM in the northwest Pacific (161°E) and ~2 nM in the Bering Sea (57°N, 180°E). The deep water concentrations for Ni and Zn in the Bering Sea were also 1.3–2 times higher than in the North Pacific. The profiles for Co and Cu were examined in the subarctic North Pacific, and results obtained were consistent with previous reports. There was a significant correlation between the concentrations of Co and Mn except for surface mixed layer. The profiles for total adsorbable Mn were similar to the reported profiles for total dissolvable Mn. The deep water concentration of Mn in the Bering Sea was also 4 times higher than in the North Pacific. Iron and zinc were depleted in surface water of the subarctic North Pacific. The relationship between these trace elements and nutrients suggests that these elements could be a limiting factor of phytoplankton productivity. In the Bering Sea, surface water contained ~0.3 nM of Fe. The Zn concentration, which was less than the detection limit in surface water, increased at shallower depths (~30 m) compared with the subarctic North Pacific. These results imply a higher flux of Fe and Zn to surface water in the Bering Sea. This in turn may cause the ecosystem in the Bering Sea characterized by a dominance of diatoms and high regenerated production.

Development of a deep-sea in situ Mn analyzer and its application for hydrothermal plume observation

Abstract This paper presents the first in situ flow-through chemical analyzer using a chemiluminescence (CL) method in the deep sea to a depth of 5200 m. The analyzer, called GAMOS (Geochemical Anomalies MOnitoring System), determines the concentration of dissolved manganese continuously using a H 2 O 2 –luminol CL method. A detection limit of 0.23 nM was obtained. The GAMOS was used successfully for hydrothermal plume observation.

Automated determination of vanadium(IV) and (V) in natural waters based on chelating resin separation and catalytic detection with Bindschedler’s green leuco base

An automated method for determining V(V) and V(IV) in natural waters has been developed. The method is based on the combination of a selective column extraction using two kinds of chelating resins and an air-segmented continuous flow analysis (ASCFA) using catalytic detection with Bindschedler’s green leuco base (BGL)–KBrO3 system. Based on this method, V(V) in a sample solution at pHs from 2.2 to 3.8 is selectively collected on an acetylacetone-immobilized resin and then V(IV) in the eluent is collected on an 8-quinolinole-immobilized resin separating it from iron species, which interfere with the ASCFA detection. V(V) and V(IV) are successively eluted with diluted hydrochloric acid and the resulting eluent is carried into the ASCFA. The concentrations of vanadium species are determined from the absorbance of BGL. The detection range for vanadium species was 0.05–15.0 nM and the standard deviations at 5.0 nM were 1.1% for V(IV) and 0.9% for V(V), respectively. The method was successfully applied to study the behavior of vanadium species in natural waters.

Dissolved organic carbon and fluorescence in Lake Hovsgol : factors reducing humic content of the lake water

Abstract Lake Hovsgol is a large tectonic lake located in northern Mongolia, which has extremely transparent lake water. In our survey, the dissolved organic carbon of the lake water was 80–100 μM-C, and the fluorescence intensity in an excitation and emission matrix was very low. The brown color and high content of humic substances in river water flowing from a watershed consisting of grassland and forests rapidly declined in the coastal area of the lake. The decrease in humic content may be due not only to dilution by the lake water but also to flocculation and photobleaching. Among tectonic lakes in Asia, Lake Hovsgol would appear to have unique biological and hydrological features that reduce humic content and help to maintain water transparency.

The production-to-respiration ratio and its implication in Lake Biwa, Japan

Production-to-respiration (P:R) ratio was estimated at an offshore site of Lake Biwa in order to examine whether the plankton and benthic community is subsidized with allochthonous organic carbon, and to clarify the role of this lake as potential source or sink of carbon dioxide. The respiration rate of protozoan and metazoan plankton was calculated from their biomass and empirical equations of oxygen consumption rates, and that of bacterioplankton was derived from their production rate and growth efficiency. In addition, the carbon mineralization rate in the lake sediments was estimated from the accumulation rate of organic carbon, which was determined using a 210Pb dating technique. On an annual basis, the sum of respiration rates of heterotrophic plankton was comparable to net primary production rate measured by the 13C method. However, when the mineralization rate in the lake sediments was included, the areal P:R ratio was 0.89, suggesting that Lake Biwa is net heterotrophic at the offshore site with the community being subsidized with allochthonous organic carbon. Such a view was supported by the surface water pCO2 that was on average higher than that of the atmosphere. However, the estimate of net CO2 release rate was close to that of carbon burial rate in the sediments. The result suggests that the role of Lake Biwa in relation to atmospheric carbon is almost null at the offshore site, although the community is supported partially by organic carbon released from the surrounding areas.

The budget of dissolved trace metals in Lake Biwa, Japan

A comprehensive study on the dynamics of dissolved elements (Mg, Al, Si, P, Ca, V, Cr, Mn, Fe, Ni, Zn, As, Sr, Y, W, and U) in Lake Biwa was carried out using a clean technique. Lake water samples (n = 523) were collected from six stations in the North Basin and three stations in the South Basin. River water samples (n = 178) were collected from 14 major rivers flowing into the North Basin. Rainwater samples (n = 89) were collected at Otsu. The river water was enriched with Mn, Al, Fe, P, and Zn and the rainwater was enriched with Zn, Al, Fe, and Mn compared to North Basin water during winter mixing. The residence times of dissolved species were estimated on the basis of input through the rivers and rain. The residence times for Ca, Mg, and Sr were about 8 years, the same as that for water. Mn, Al, Fe, and Zn showed the shortest residence times (0.05–0.19 year). A budget calculation suggested that more than 60% of the input of dissolved Si, P, V, Cr, Mn, Fe, Ni, and Zn was scavenged and retained in the lake sediments and/or discharged as suspended particles.

Flow-through analysis of Al in seawater by fluorometric detection with the use of Lumogallion

A flow-through analytical method has been developed for the determination of trace amounts of aluminum in seawater with the use of Lumogallion fluorometric detection. Because iron was selectively removed by passing the sample through an 8-quinolinol immobilized chelating resin column (MAF-8HQ), this method could be applied to samples collected at the hydrothermal oceanic regime. Several known organic complexing agents were studied as a model group to examine the effect of naturally occurring organic ligands on the detection of aluminum in seawater. The detection limit was 0.17 nM for 10 ml of sample. The standard deviation was 2.7% at 2 nM of aluminum. This method permitted the sensitive, precise, and rapid determination of subnanomolar Al in seawater without contamination onboard ship.

Assessment of the Status of Groundwater Arsenic at Singair Upazila, Manikganj Bangladesh; Exploring the Correlation with Other Metals and Ions

Comparative study was conducted to correlate arsenic (As), iron (Fe), copper (Cu), manganese (Mn), calcium (Ca2+), magnesium (Mg2+), potassium (K+), nitrate (NO3−), phosphate (PO43−), and ammonia (NH3) by determining their concentration at different depths of the tube-wells in the selected study area at Singair, Manikganj Bangladesh. Total 99 tube-well water samples were collected from the study area. In most of the sampling points, the present concentrations of As were less than the previous concentrations. The correlation between As and Fe was positively significant. It can be suggested possible adsorption/co-precipitation of As with Fe in shallow aquifer. However, the relationship between As and Mn was not significantly observed. On the other hand, relationship between Cu and As showed a positive significant correlation. The correlation between As and PO43− was also significant, although the correlation between As and NO3− was not significant. PO43− may come from phosphate fertilizers application and can be a contributor of As in the shallow aquifer. The PCA biplot also indicated the significant relationship between As, Cu, Fe and PO43−. Excessive withdrawal of tube-well water along with aquifer dynamics and ionic interference might be responsible for the mobilization of As in the study area.

Seasonal characteristics of surface water fulvic acids from Lake Biwa and Lake Tankai in Japan

Seasonal characteristics of surface water fulvic acids (FAs) isolated from Japanese clear-water lakes were investigated. Qualitative changes in Lake Biwa and Lake Tankai FAs were determined and compared. Although the relative molecular weights determined by high-performance size-exclusion chromatography did not change remarkably, the elemental compositions,