The effects of possible contamination by sample holders on samples to be returned by Hayabusa2     

Naoki Shirai  Yuzuru Karouji  Kazuya Kumagai  Masayuki Uesugi  Kaori Hirahara  Motoo Ito  Naotaka Tomioka  Kentaro Uesugi  Akira Yamaguchi  Naoya Imae  Takuji Ohigashi  Toru Yada  Masanao Abe 《Meteoritics & planetary science》2020,55(7):1665-1680

Chemical compositions of materials used for new sample holders (vertically aligned carbon nanotubes [VACNTs] and polyimide film), which were developed for the analysis of Hayabusa2‐return samples, were determined by instrumental neutron activation analysis and/or instrumental photon activation analysis, to estimate contamination effects from the sample holders. The synthetic quartz plate used for the sample holders was also analyzed. Ten elements (Na, Al, Cr, Mn, Fe, Ni, Eu, W, Au, and Th) and 14 elements (Na, Al, K, Sc, Ti, Cr, Zn, Ga, Br, Sb, La, Eu, Ir, and Au) could be detected in the VACNTs and polyimide film, respectively. The VACNT data show that contamination by this material with respect to the Murchison meteorite is negligible in terms of the elemental ratios (e.g., Fe/Mn, Na/Al, and Mn/Cr) used for the classification of meteorites due to the extremely low density of VACNTs. However, for the Au/Cr ratio, even small degrees (1.7 wt%) of contamination by VACNTs will change the Au/Cr ratio. Elemental ratios used for the classification of meteorites are only influenced by large amounts of contamination (>60 wt%) of polyimide film, which is unlikely to occur. In contrast, detectable effects on Ti isotopic compositions are caused by >0.1 and >0.3 wt% contamination by VACNTs and polyimide film, respectively, and Hf isotopic changes are caused by >0.1 wt% contamination by VACNTs. The new sample holders (VACNTs and polyimide film) are suitable for chemical classification of Hayabusa2‐return samples, because of their ease of use, applicability to multiple analytical instruments, and low contamination levels for most elements.  相似文献   

Theoretical and experimental investigation of nickel isotopic fractionation in species relevant to modern and ancient oceans     

Toshiyuki Fujii  Frédéric Moynier  Minori Abe 《Geochimica et cosmochimica acta》2011,75(2):469-7643

Nickel plays a central role as an enzyme co-factor in the metabolism of methanogenic Archaea. Methanogens can fractionate Ni isotopes during assimilation, opening the possibility of using the stable isotopic composition of Ni as a biomarker. However, other sources of Ni isotopic variations need to be evaluated before one can establish Ni isotopes as an unambiguous tracer of methanogenesis in the rock record. Equilibrium exchange of Ni between the different species present in the ocean is a potential source of isotopic fractionation. Through controlled laboratory experiments and theoretical calculations, we quantify equilibrium Ni isotope fractionation between different species relevant to the modern and ancient ocean: Ni(H₂O)₆²⁺, Ni(H₂O)₁₈²⁺, NiOH(H₂O)₅⁺, Ni(OH)₂(H₂O)₄, NiCl(H₂O)₅⁺, cis-NiCl₂(H₂O)₄, trans-NiCl₂(H₂O)₄, NiHS(H₂O)₅⁺, Ni(HS)₂(H₂O)₄, NiSO₄(H₂O)₄, NiHCO₃(H₂O)₄⁺, NiCO₃(H₂O)₄, and organic ligands (crown ether and oxalic acid). The magnitude of ligand-controlled Ni isotopic fractionation, approximately 1.25‰/amu (2.5‰ for the ⁶⁰Ni/⁵⁸Ni ratio), is similar to that previously measured in cultures of methanogenic Archaea.  相似文献   

Breaking Up: Comminution Mechanisms in Sheared Simulated Fault Gouge   总被引：1，自引：0，他引：1  

K. Mair  S. Abe 《Pure and Applied Geophysics》2011,168(12):2277-2288

The microstructural state and evolution of fault gouge has important implications for the mechanical behaviour, and hence the seismic slip potential of faults. We use 3D discrete element (DEM) simulations to investigate the fragmentation processes operating in fault gouge during shear. Our granular fault gouge models consist of aggregate grains, each composed of several thousand spherical particles stuck together with breakable elastic bonds. The aggregate grains are confined between two blocks of solid material and sheared under a given normal stress. During shear, the grains can fragment in a somewhat realistic way leading to an evolution of grain size, grain shape and overall texture. The ‘breaking up’ of the fault gouge is driven by two distinct comminution mechanisms: grain abrasion and grain splitting. The relative importance of the two mechanisms depends on applied normal stress, boundary wall roughness and accumulated shear strain. If normal stress is sufficiently high, grain splitting contributes significantly to comminution, particularly in the initial stages of the simulations. In contrast, grain abrasion is the dominant mechanism operating in simulations carried out at lower normal stress and is also the main fragmentation mechanism during the later stages of all simulations. Rough boundaries promote relatively more grain splitting whereas smooth boundaries favor grain abrasion. Grain splitting (plus accompanying abrasion) appears to be an efficient mechanism for reducing the mean grain size of the gouge debris and leads rapidly to a power law size distribution with an exponent that increases with strain. Grain abrasion (acting alone) is an effective way to generate excess fine grains and leads to a bimodal distribution of grain sizes. We suggest that these two distinct mechanisms would operate at different stages of a fault’s history. The resulting distributions in grain size and grain shape may significantly affect frictional strength and stability. Our results therefore have implications for the earthquake potential of seismically active faults with accumulations of gouge. They may also be relevant to the susceptibility of rockslides since non-cohesive basal shear zones will evolve in a similar way and potentially control the dynamics of the slide.  相似文献   

Under‐ice salinity and stable isotope distribution of Saroma‐ko Lagoon,Hokkaido, northern Japan     

Maki Morimoto  Kyoko Kawanobe  Osamu Abe  Takayoshi Kawai  Toshiyuki Kawamura  Kunio Shirasawa 《水文研究》2010,24(7):904-916

In winter, lakes and lagoons at high altitudes or high latitudes have interesting hydrological cycles that differ from those in other seasons or in other regions, because water surfaces are covered with ice. Hydrological balances of lakes and lagoons are complex dynamic systems, and to elucidate them, isotopic tracers of water have been used as effective tools along with observations of precipitation, evaporation, inflows, and outflows. Here, to understand hydrological processes during freezing periods in the brackish Saroma‐ko Lagoon, Hokkaido, northern Japan, we examined horizontal and vertical distributions of salinity and isotope compositions of lagoon water and ice in 2005 and 2006. Horizontal and vertical gradients of salinity and isotope compositions were observed from the river mouth to the sea channel, and factors determining these distributions were considered. The mixing of freshwater and seawater and a freezing effect were presumed to be factors in relationships between salinity and isotopes and in relationships between surface waters and ice just above the water. A simple box model for water balance was constructed based on these putative factors to reproduce the distributions of salinity and isotope compositions of surface waters and ice. An evaluation of the model revealed that this hydrological system is controlled primarily by horizontal advection of the epilimnion, freshwater influx, and the ice growth rate. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Dynamics of pelagic variables in two contrasting coastal systems in the western Hokkaido coast off Otaru port,Japan     

Julius I. Agboola  Mario Uchimiya  Isao Kudo  Kazuo Kido  Masato Osawa 《Estuarine, Coastal and Shelf Science》2010,86(3):477-484

Human impact on adjacent coastal waters, leading to alteration in nutritional environment and hence affecting phytoplankton biomass (Chlorophyll a), will probably be enhanced by the nearby presence of ports. The main goal of this study is to assess the influence of nearby presence of port on phytoplankton biomass build-up and the physical–chemical environmental characteristics in two contrasting coastal systems (Otaru port, S-IN and an exposed coastal area, S-OUT) in the western Hokkaido coast off Otaru port, Japan. Sampling was conducted on “bi-weekly and monthly” basis during the period of September 2006–December 2007 and data comprising 11 pelagic variables were obtained. In most instance, phytoplankton biomass, nutrients' (NH₄, NO₃, PO₄, and Si(OH)₄) concentrations and nutrients' molar ratios were higher at the Otaru port location. Physical parameters (temperature, salinity, hydrogen ion concentration (pH), photosynthetically active radiation (PAR) and dissolved oxygen, (DO)) were not significantly different (P > 0.05) between the two locations. With the exception of salinity, pH and DIC, all variables measured showed significant variation (P < 0.05) with season. While the coefficient of variation (CV) of physical parameters and phytoplankton biomass were relatively higher in Otaru port location (S-IN), the exposed coastal location (S-OUT) showed a higher variation in chemical parameters. Other variables showed different patterns between the two locations. We conclude that ports, due to its activities and restricted circulation favour high nutrient loading and phytoplankton biomass build-up in adjacent coastal systems, thus, suggesting the need for continuous field observation data in order to advance our knowledge on possible future human impact on coastal environment and the need to monitor and control port activities.  相似文献   

Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal   总被引：4，自引：4，他引：0  

Akihiro Hachikubo  Oleg Khlystov  Alexey Krylov  Hirotoshi Sakagami  Hirotsugu Minami  Yutaka Nunokawa  Satoshi Yamashita  Nobuo Takahashi  Hitoshi Shoji  Shin’ya Nishio  Masato Kida  Takao Ebinuma  Gennadiy Kalmychkov  Jeffrey Poort 《Geo-Marine Letters》2010,30(3-4):321-329

We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ¹³C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ¹³C signatures at two sites where ethane δ¹³C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which ¹³C and deuterium were both highly depleted (mean δ¹³C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C₂ δ¹³C–δD classification for hydrate-bound gas in either freshwater or marine environments.  相似文献   

Deep water observations of extreme waves with moored and free GPS buoys   总被引：1，自引：1，他引：0  

Takuji Waseda  Masato Sinchi  Keiji Kiyomatsu  Tomoya Nishida  Shunsuke Takahashi  Sho Asaumi  Yoshimi Kawai  Hitoshi Tamura  Yasumasa Miyazawa 《Ocean Dynamics》2014,64(9):1269-1280

Point-positioning GPS-based wave measurements were conducted by deep ocean (over 5,000 m) surface buoys moored in the North West Pacific Ocean in 2009, 2012, and 2013. The observed surface elevation bears statistical characteristics of Gaussian, spectrally narrow ocean waves. The tail of the averaged spectrum follows the frequency to the power of ?4 slope, and the significant wave height and period satisfies the Toba’s 3/2 law. The observations compare well with a numerical wave hindcast. Two large freak waves exceeding 13 m in height were observed in October 2009 and three extreme waves around 20 m in height were observed in October 2012 and in January 2013. These extreme events are associated with passages of a typhoon and a mid-latitude cyclone. Horizontal movement of the buoy revealed that the orbital motion of the waves at the peak of the wave group mostly exceed the weakly nonlinear estimate. For some cases, the orbital velocity exceeded the group velocity, which might indicate a breaking event but is not conclusive yet.  相似文献   

Raman spectroscopic and calorimetric observations on natural gas hydrates with cubic structures I and II obtained from Lake Baikal     

Akihiro Hachikubo  Oleg Khlystov  Masato Kida  Hirotoshi Sakagami  Hirotsugu Minami  Satoshi Yamashita  Nobuo Takahashi  Hitoshi Shoji  Gennadiy Kalmychkov  Jeffrey Poort 《Geo-Marine Letters》2012,32(5-6):419-426

This study reports measurements of the Raman spectra of Lake Baikal gas hydrates and estimations of the hydration number of methane-rich samples. The hydration number of gas hydrates retrieved from the southern Baikal Basin (crystallographic structure I) was approx. 6.1. Consistent with previous results, the Raman spectra of gas hydrates retrieved from the Kukuy K-2 mud volcano in the central Baikal Basin indicated the existence of crystallographic structures I and II. Measurements of the dissociation heat of Lake Baikal gas hydrates by calorimetry (from the decomposition of gas hydrates to gas and water), employing the hydration number, revealed values of 53.7–55.5?kJ?mol^–1 for the southern basin samples (structure I), and of 54.3–55.5?kJ?mol^–1 for the structure I hydrates and 62.8–64.2?kJ?mol^–1 for the structure II hydrates from the Kukuy K-2 mud volcano.  相似文献   

Thermal anomalies associated with shallow gas hydrates in the K-2 mud volcano, Lake Baikal     

Jeffrey Poort  Oleg M. Khlystov  Lieven Naudts  Albert D. Duchkov  Hitoshi Shoji  Shin’ya Nishio  Marc De Batist  Akihiro Hachikubo  Masato Kida  Hirotsugu Minami  Andrey Y. Manakov  Marina V. Kulikova  Alexey A. Krylov 《Geo-Marine Letters》2012,32(5-6):407-417

Thermal measurements and hydrate mapping in the vicinity of the K-2 mud volcano in Lake Baikal have revealed a particular type of association of thermal anomalies (29–121?mW?m^–2) near hydrate-forming layers. Detailed coring within K-2 showed that hydrates are restricted to two distinct zones at sub-bottom depths exceeding 70–300?cm. Temperature data from stations with hydrate recovery and degassing features all display low thermal gradients. Otherwise, the thermal gradients within the mud volcano are generally increased. These findings imply a more complicated thermal regime than often assumed for mud volcanoes, with important roles for both fluids and hydrates. The coexistence of neighbouring low and high thermal anomalies is interpreted to result from discharging and recharging fluid activity, rather than hydrate thermodynamics. It is suggested that hydrates play a key role in controlling the fluid circulation pattern at an early stage. At a later stage, the inflow of undersaturated lake water would favour the dissolution of structure I hydrates and the formation of structure II hydrates, the latter having been observed on top of structure I hydrates in the K-2 mud volcano.  相似文献   

Perturbed physics ensemble using the MIROC5 coupled atmosphere–ocean GCM without flux corrections: experimental design and results     

Hideo Shiogama  Masahiro Watanabe  Masakazu Yoshimori  Tokuta Yokohata  Tomoo Ogura  James D. Annan  Julia C. Hargreaves  Manabu Abe  Youichi Kamae  Ryouta O’ishi  Rei Nobui  Seita Emori  Toru Nozawa  Ayako Abe-Ouchi  Masahide Kimoto 《Climate Dynamics》2012,39(12):3041-3056

In this study, we constructed a perturbed physics ensemble (PPE) for the MIROC5 coupled atmosphere–ocean general circulation model (CGCM) to investigate the parametric uncertainty of climate sensitivity (CS). Previous studies of PPEs have mainly used the atmosphere-slab ocean models. A few PPE studies using a CGCM applied flux corrections, because perturbations in parameters can lead to large radiation imbalances at the top of the atmosphere and climate drifts. We developed a method to prevent climate drifts in PPE experiments using the MIROC5 CGCM without flux corrections. We simultaneously swept 10 parameters in atmosphere and surface schemes. The range of CS (estimated from our 35 ensemble members) was not wide (2.2–3.2?°C). The shortwave cloud feedback related to changes in middle-level cloud albedo dominated the variations in the total feedback. We found three performance metrics for the present climate simulations of middle-level cloud albedo, precipitation, and ENSO amplitude that systematically relate to the variations in shortwave cloud feedback in this PPE.  相似文献