Study of Water Motion at the Dissolved Oxygen Minimum Layer and Local Oxygen Consumption Rate from the Lagrangian Viewpoint

By using the Euler-Lagrangian method, we examine water movements within the layer of minimum oxygen concentration and estimate local oxygen consumption rates for 15 regions of the global ocean. To do this, a number of labeled particles (which represent water parcels) are deployed at the center of a grid with 15 depth levels and tracked backward in time for 50 years in a three-dimensional velocity field. We assume that a particle picks up oxygen when it encounters the point of maximum oxygen concentration along the 50 years segment of its path. We introduce a contribution rate from waters distributed throughout the global ocean to the oxygen concentration of a local layer under consideration. Water parcels which are assumed to pick up oxygen within the oxygen minimum layer of an oceanic region under consideration make a very small contribution to the overall oxygen concentration of this layer. In addition, these parcels move out of the layer and water parcels from the upper layers take their place. The averaged Lagrangian local oxygen consumption rate is 0.033 ml/l/yr for the depth of the oxygen minimum layer, 0.20 ml/l/yr at 100 m depth (euphotic layer), 0.043 ml/l/yr for layers from 150 m to 800 m depth and 0.012 ml/l/yr for deep layers from 800 m to 3000 m. The present Lagrangian numerical experiment produces a maximum difference between observed and calculated concentrations of oxygen and, therefore, a maximum oxygen consumption rate. Although the present method has an ambiguity as to how oxygen is picked up, we nevertheless were able to identify regions in which the water parcels pick up oxygen of maximum concentration. We found that the South Equatorial Current (SEC) transports oxygen of higher concentration to the middle latitude regions of both the North Atlantic and the North Pacific across the equator.     

The distribution of manganese and iron between ilmenite and granitic magma in the Ôsumi Peninsula,Japan

Manganoan ilmenite with a variable manganese content occurs as an early accessory constituent of granitic rocks in the Ôsumi Peninsula, southern Kyushu. Electron probe micro-analysis of a grain containing highest manganese gives the structural formula (Fe _1.23 ²⁺ Mn _0.81 ²⁺ ) (Ti_1.97) O₆, if all of the manganese and iron are in the divalent state. The manganese content of manganoan ilmenite increases with an increase of the differentiation index of host rocks, however, the amount of ilmenite tends to decrease with the increase of the same index. The mode of occurrence of the ilmenite suggests that it is the first mafic mineral to precipitate from the magma. The average value of the distribution coefficient of manganese and ferrous iron between ilmenite and granitic magma is 5.5, if the Mn/Fe ratio of the granitic rocks represents that of granitic magma. The variation in the FeO and MnO contents against the differentiation index for granitic rocks of the Ôsumi Peninsula, and the value of the distribution coefficient, show that high manganoan ilmenite is stable in the most differentiated granitic rock of the Ôsumi Peninsula.     

Determination of Ge, As, Se and Te in Silicate Samples Using Isotope Dilution-Internal Standardisation Octopole Reaction Cell ICP-QMS by Normal Sample Nebulisation

A method for the determination of Ge, As, Se and Te in silicate samples using isotope dilution-internal standardisation (ID-IS) octopole reaction cell (ORC) ICP-QMS by normal sample nebulisation was developed. The method does not involve either hydride generation or ion exchange. Germanium, Se and Te were determined by isotope dilution (ID), and As was determined by ID-IS. A silicate sample with an added Ge-Se-Te spike was digested with an HF-HNO₃-HBr mixture, dried, re-dissolved with HF and the supernatant liquid was directly aspirated into an ORC-ICP-QMS instrument with He or H₂ gas. No matrix effects were observed down to a dilution factor (DF) of ∼ 70 for Ge, Se and Te and DF of ∼ 1000 for As, which resulted in 3s detection limits in silicates of 2, 1, 0.1 and 4 ng g⁻¹, respectively. Advantages of the method are the simple sample introduction as well as a capability of determining S, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by ID-IS-ICP-QMS/SFMS from the same solution. Furthermore, the total sample solution consumption was only 0.253 ml with DF = 2000. Therefore, only a 0.13 mg test portion was required. To demonstrate the applicability of this technique, Ge, As, Se and Te in eight silicate reference materials were determined, as well as S, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta in four carbonaceous chondrites.     

Impact of tropical and subtropical SSTs on mid-latitude tropospheric warming in the northern summer of 2010

The relationship between mid-latitude tropospheric warming (MLTW) and the tropical sea surface temperatures (SSTs) in June–August (JJA) of 2010 has been investigated using an atmospheric general circulation model forced with the evolving observed SSTs. The simulation results indicate that the SST anomalies (SSTAs) in the equatorial Pacific in JJA 2010, indicating La Niña condition, did not contribute simultaneously to produce the MLTW in JJA 2010, and, instead, the SSTAs in the northern subtropics (the whole latitudinal band between 10°N and 30°N) contributed. However, it is shown by the results that enough magnitude of the atmospheric height anomalies over the northern mid-latitude was not reproduced by the SSTAs over the northern subtropical Indo-western Pacific (IWP) alone or over the northern subtropical Atlantic alone. It implies that both the SSTA over the northern subtropics of IWP and Atlantic were necessary to reproduce the MLTW. The possible role of convective activity for the MLTW is also discussed.     

ENSO modulation by mountain uplift

How climate changes will modify the behavior of El Niño/Southern Oscillation (ENSO) is one of the important questions in future climate projections. An investigation under different climate forcing gives us a good insight on the mechanism of ENSO variability and its changes. In this paper, sensitivity on ENSO by progressive mountain uplift is investigated with an atmosphere–ocean coupled general circulation model. We used eight different mountain heights: 0% (no mountain), 20, 40, 60, 80, 100 (control run), 120, and 140%. Land–sea distribution is the same for all experiments and all mountains in the world are uniformly varied. Systematic changes in precipitation and circulation fields as well as SST are obtained with progressive mountain uplift. In the summertime, the precipitation area moved inland of the Asian continent with mountain uplift, while the Pacific subtropical anticyclone and associated trade winds became stronger. The western Pacific warm pool and ENSO also systematically changed. When the mountain height is low, a warm pool is located over the central Pacific due to weak trade winds in the Pacific. The model ENSO is strongest, its frequency longest, and is most periodic in the no mountain run. The model ENSO becomes weaker, shorter and less periodic when the mountain height increases. Strengthening the mean state trade winds and narrowing meridional extent of equatorial wind and ocean response by mountain uplift would be responsible for ENSO modulation.     

Characteristics of rainfall systems accompanied with Changma front at Chujado in Korea

The rainy season from June to July in the East Asia is called the Changma in Korea, the Meiyu in China, or the Baiu in Japan. The mesoscale convective systems which occur near a front frequently lead to severe weather phenomenon such as localized gust and heavy rainfall. An intensive field experiment was conducted at Chujado (33.95°N, 126.28°E) to find out the characteristics of the precipitating system using information such as the raindrop size distribution, kinematic features during a Changma period between June 21 2007 and July 11 2007. Different characteristics of three identified rainfall cases in a Changma frontal precipitation system occurred from 5 to 6 July in 2007 at Chujado area have been identified. Based on the radar reflectivity and raingage at Chujado, each rainfall system maintained for 7 hours, 4 hours, and 9 hours, respectively. According to the analysis of a total vertical wind shear (TVWS) and a directional vertical wind shear (DVWS), the temperature gradient was the strongest near the surface and both warm and cold advections were occurred in all cases but at different levels. The deep warm advection was related to the longer rainfall lifetime and stronger rainrate, but smaller raindrop size. The unstable atmospheric condition, which has cold advection at the surface and warm advection in higher level, caused the larger size diameter of raindrop. The echo top height of 30 dBZ was around 6 km in the two rainfall systems and around 4 km in the other one. The number concentrations of raindrop has turning point at the drop size of 2 mm in diameter. The stronger (weaker) updraft and downdraft were also related to the decreased number concentration of smaller (larger) size drops and increased that of the larger (smaller) drops.     

Upper Mantle Velocity Structure Estimated From Ps-Converted Wave Beneath the North-Eastern Japan Arc

Summary. The upper boundary of the descending oceanic plate is located by using PS -waves (converted from P to S at the boundary) in the Tohoku District, the north-eastern part of Honshu, Japan. the observed PS-P time data are well explained by a two-layered oceanic plate model composed of a thin low-velocity upper layer whose thickness is less than 10 km and a thick high-velocity lower layer; the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle. the estimated location of the upper boundary is just above the upper seismic plane of the double-planed deep seismic zone. This result indicates that events in the upper seismic plane, at least in the depth range from 60 to 150 km, occur within the thin low-velocity layer on the surface of the oceanic plate.     

Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in ¹¹B relative to ¹⁰B (δ¹¹B = −1.2 to +7.7) and ⁷Li relative to ⁶Li (δ⁷Li = −1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (δ¹¹B = −16.6 to −2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle.     

Suppression of Matrix Effects in ICP-MS by High Power Operation of ICP: Application to Precise Determination of Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U at ng g-1 Levels in Milligram Silicate Samples

We found that the suppression of signals for ⁸⁸Sr, ¹⁴⁰Ce and ²³⁸U in rock solution caused by rock matrix in ICP-MS (matrix effects) was reduced at high power operation (1.7 kW) of the ICP. To make the signal suppression by the matrix negligible, minimum dilution factors (DF) of the rock solution for Sr, Ce and U were 600, 400 and 113 at 1.1, 1.4 and 1.7 kW, respectively. Based on these findings, a rapid and precise determination method for Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U using FI (flow injection)-ICP-MS was developed. The amount of the sample solution required for FI-ICP-MS was 0.2 ml, so that 1.8 mg sample was sufficient for analysis with a detection limit of several ng g^-1. Using this method, we determined the trace element concentrations in the USGS rock reference materials, DTS-1, PCC-1, BCR-1 and AGV-1, and the GSJ rock reference materials, JP-1, JB-1, -2, -3, JA-1, -2 and -3. The reproducibilities (RSD %) in replicate analyses (n=5) of BCR-1, AGV-1, JB-1, -2, -3, JA-1, -2, and -3 were < 6 %, and typically 2.5%. The difference between the average concentrations of this study for BCR-1 and those of the reference values were < 2%. Therefore, it was concluded that the method can give reliable data for trace elements in silicate rocks.