Isotope fractionation of neon during stepheating extraction?: a comment on ‘Re‐interpretation of the existence of a primitive plume under Australia based on neon isotope fractionation during step heating’ by Gautheron and Moreira (2003)

Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re‐interpreted the plume‐like neon isotopic compositions found in metasomatic apatite from a south‐eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh‐type isotope fractionation of originally MORB‐type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume‐like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion.     

Measuring the k–S–p relations on DNAPLs migration

Migration characteristics of dense non-aqueous phase liquids (DNAPLs) in the subsurface can be expressed as a water–DNAPL two-phase system based on mainly the k–S–p relations, which describe the relations among relative permeability (k), degree of water saturation (S), and capillary pressure head (p). The aims of this research are to develop an experimental system with new type of probes, such as the electrical conductivity probe for measuring the degree of water saturation and the hydrophilic and hydrophobic tensiometer for measuring the pore water and DNAPL pressures, and also to estimate the results obtained from the developed experimental system. From these tests, the excellent k–S–p relations were obtained and the efficiency and validity of this developed experimental system have been confirmed in terms of the concept of the scaling coefficient calculated by interfacial tensions.     

泰国北部三叠系Lampang群Doi Long组的有孔虫组合与沉积环境

A rich foraminiferal assemblage, consisting of abundant Aulotortus sinuosus and A. tumidus in association with Lamelliconus multispirus, Endoteba ex gr. controversa, E. ex gr. badouxi, Endotebanella kocaeliensis, Endotriada tyrrhenica, Endotriadella wirzi, Malayspirina fontainei, Ammobaculites rhaeticus, Diplotremina astrofimbriata, Agathammina austroalpina, and others, was found in the Doi Long Formation of the Triassic Lampang Group, Northern Thailand. These foraminifers suggest that the formation is referable to the Carnian (early Late Triassic), which is consistent with the age estimated by ammonoids. In microfacies, peloidal grainstone, bioclastic grainstone, sponge-microbial boundstone, and oolitic grainstone were recognized in the Doi Long Formation. Based on microfacies, three depositional facies, the lagoon facies, reef facies, and shoal facies, are recognized in this formation. These lines of evidence are suggestive that the Doi Long Formation was deposited in a reef or bank setting rather than a ramp setting.     

Recent hydrological and geochemical research for earthquake prediction in Japan

Hydrological and geochemical studies for earthquake prediction in Japan during the last two decades are reviewed. Following the 1995 Hyogo-ken Nanbu (Kobe) earthquake, the central approach to research on earthquake prediction was modified. Instead of precursory detection, emphasis was placed on understanding the entire earthquake cycle. Moreover, the prediction program for the anticipated Tokai earthquake was revised in 2003 to include the detection of preslip-related precursors. These changes included the promotion of the following hydrological and geochemical studies for earthquake prediction: (1) development and/or application of statistical methods to extract small fluctuations from hydrological/geochemical data, (2) evaluation of the detectability of preslip-related anomalies in terms of groundwater levels in wells in the Tokai region, and (3) establishment of a new groundwater and borehole strain observation network for Nankai and Tonankai earthquake prediction research. The following basic geochemical studies were carried out: (1) development of a new monitoring system using a quadrupole mass spectrometer, (2) experimental studies on hydrogen generation by the grinding of rock and crystal powders, (3) comprehensive monitoring of groundwater gas and precise crustal deformation, and (4) mantle-derivative helium observation to compare with seismic velocity structures and the distribution of non-volcanic tremors. Moreover, hydrological and geochemical investigations related to the evolution of fault zones were introduced within the framework of fault zone drilling projects.     

Seasonal variations in the nitrogen isotopic composition of settling particles at station K2 in the western subarctic North Pacific

Intensive observations using hydrographical cruises and moored sediment trap deployments during 2010 and 2012 at station K2 in the North Pacific Western Subarctic Gyre (WSG) revealed seasonal changes in δ ¹⁵N of both suspended and settling particles. Suspended particles (SUS) were collected from depths between the surface and 200 m; settling particles by drifting sediment traps (DST; 100–200 m) and moored sediment traps (MST; 200 and 500 m). All particles showed higher δ ¹⁵N values in winter and lower in summer, contrary to the expected by isotopic fractionation during phytoplankton nitrate consumption. We suggest that these observed isotopic patterns are due to ammonium consumption via light-controlled nitrification, which could induce variations in δ ¹⁵N(SUS) of 0.4–3.1 ‰ in the euphotic zone (EZ). The δ ¹⁵N(SUS) signature was reflected by δ ¹⁵N(DST) despite modifications during biogenic transformation from suspended particles in the EZ. δ ¹⁵N enrichment (average: 3.6 ‰) and the increase in C:N ratio (by 1.6) in settling particles suggests year-round contributions of metabolites from herbivorous zooplankton as well as TEPs produced by diatoms. Accordingly, seasonal δ ¹⁵N(DST) variations of 2.4–7.0 ‰ showed a significant correlation with primary productivity (PP) at K2. By applying the observed δ ¹⁵N(DST) vs. PP regression to δ ¹⁵N(MST) of 1.9–8.0 ‰, we constructed the first annual time-series of PP changes in the WSG. This new approach to estimate productivity can be a powerful tool for further understanding of the biological pump in the WSG, even though its validity needs to be examined carefully.     

Improved Method for Calculating Anthropogenic CO2 in the Upper Layer of the North Pacific Subtropical Gyre along 175°E

Seawater samples were collected in the North Pacific along 175°E during a cruise of the Northwest Pacific Carbon Cycle Study (NOPACCS) program in 1994. Many properties related to the carbonate system were analyzed. By using well-known ratios to correct for chemical changes in seawater, the CO₂ concentration at a given depth was back calculated to its initial concentration at the time when the water left the surface in winter. We estimated sea-surface CO₂ and titration alkalinity (TA) in present-day winter, from which we evaluated the degree of air-sea CO₂ disequilibrium in winter was. Using a correction factor for air-sea CO₂ disequilibrium in winter, we reconstructed sea-surface CO₂ in pre-industrial times. The difference between the back-calculated initial CO₂ and sea-surface CO₂ in pre-industrial times should correspond to anthropgenic CO₂ input. Although the mixing of different water masses may cause systematic error in the calculation, we found that the nonlinear effect induced by the mixing of different water masses was negligible in the upper layer of the North Pacific subtropical gyre along 175°E. The results of our improved method of assessing the distribution of anthropogenic CO₂ in that region show marked differences from those obtained using the previous back-calculation method.     

Bottom pressure change associated with the 2004–2005 large meander of the Kuroshio south of Japan

A large meander of the Kuroshio was generated in the region off the southern coast of Japan in August 2004 and continued until approximately July 2005. The formation and decay of the large-meander (LM) path was observed by bottom pressure (BP) sensors installed on inverted echo sounders (PIESs) and a seismic observing system off Shikoku. The variation in BP was examined focusing on the development, persistence, and decay of the LM path. The BP was found to be depressed associated with a Kuroshio path disturbance, called a small meander, and this BP depression led the sea surface height (SSH) depression by up to approximately two months. The temporal phase shift between the sea surface and deep disturbances was significantly greater than those of other small meanders that did not develop into large meanders. After the formation of the LM path, the BP beneath the Kuroshio increased with a lag of approximately two months behind the SSH elevation along with the upward displacement of the main thermocline. The increase in BP is associated with that of the positive southward BP gradient anomaly, i.e., the eastward deep Kuroshio current anomaly, which suggests an enhancement of the topographic steering and stability of the LM path. This is consistent with the fact that no small meanders occurred in the early LM period from late July 2004 to late January 2005.     

Barrier Layer and Relevant Variability of the Salinity Field in the Equatorial Pacific Estimated in an Ocean Reanalysis Experiment

This paper investigates the feasibility of an ocean data assimilation system to analyze the salinity variability associated with the barrier layer in the equatorial Pacific. In order to validate reproducibility of the temperature and salinity fields, we perform an assimilation run where some temperature and salinity observations by TRITON buoys and Argo floats are withheld. The assimilation run reproduces interannual variability of salinity in the equatorial Pacific exhibited in the data that are withheld. Statistics shows that salinity values and variations in the assimilation run are closer to the data than the climatology and in the model free run. We also confirm that zonal currents in the equatorial Pacific in the reanalysis, where all available temperature and salinity data are assimilated, are consistent with an observation-based mapping and the data of the Acoustic Doppler Current Profiler mounted on TAO buoys. Variability of the barrier layer and relevant salinity field in the reanalysis is consistent with former studies. A thick barrier layer area generally exists west of the equatorial salinity front and is displaced zonally with the migration of the front in the response to El Niño-Southern Oscillation, although the area moved to the east over the front in the 1997 El Niño. It is confirmed that the barrier layer thickness is closely correlated with the near-surface temperature in the equatorial Pacific.     

汶川地震前的b值变化

Gutenberg-Richter定理给出了地震频度随震级的分布特征.大量研究表明频度-震级关系的斜率（b值）在大地震孕育的过程中会出现减小.为了考察b值在汶川地震孕育过程中的时间演化特征,本文尝试基于破裂断层选取研究区域,考察了2000年1月至2008年4月间,汶川地震（M_S8.0）破裂区的地震活动性,并对该区域b值的变化进行了探讨.结果表明,在2005年中至2006年底,地震月频度及季度频度有一个较明显的下降.b值从2002年始至地震前呈现出一个长期趋势性减小;在地震前约半年,出现快速、显著的下降.b值的这一时间变化特征与其他研究者报道的日本东北M_W9.0级地震前的b值变化特征具有很高相似性,可能反映了大地震准备过程中的应力变化.以上结果有益于认识和理解大地震孕育演化过程,同时也表明b值在中长期地震灾害评估中具有潜在价值.

     

基于参考台的盲源分离法在抑制地磁场近场噪音中的应用研究

随着城市建设的不断发展,地磁场观测受到的人文干扰越来越严重.汽车、地铁、高铁等产生的近场噪音造成了地磁脉动等空间场源信号难以被精确观测,严重影响了地磁观测资料的实际使用价值.因此抑制这些近场噪音、提取空间场源信号具有科学意义和应用价值.本研究将远场参考法和盲源信号分离法相结合,提出了一种能有效分离空间场源信号和近场噪音的方法.首先,基于仿真分析,我们准确分离了不同特征的源信号,阐明了此方法的有效性.然后,我们将该方法应用于日本千叶地区受电车干扰较为严重的实际磁场观测数据,并选用数据质量较高的KAK国际基准台作为远场参考,实现了地磁脉动和电车干扰信号的分离,并在此基础上对观测台站的近场噪音进行了抑制.这些结果表明基于参考台的盲源信号分离法在抑制近场噪音、提取地磁场信号中是有效的,可能在电磁法勘探中具有潜在的应用价值.