Hydrogen isotopic substitution of solid methylamine through atomic surface reactions at low temperatures: A potential contribution to the D/H ratio of methylamine in molecular clouds

We experimentally studied hydrogen (H)–deuterium (D) substitution reactions of solid methylamine (CH₃NH₂) under astrophysically relevant conditions. We also calculated the potential energy surface for the H–D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18 kJ mol^?1, CH₃NH₂ reacted with D atoms to yield deuterated methylamines at 10 K, suggesting that the H–D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.     

Disastrous sediment discharge due to typhoon-induced heavy rainfall over fossil periglacial catchments in western Tokachi,Hokkaido, northern Japan

In August 2016, Typhoon 1610 (Lionrock) caused heavy rainfall in Hokkaido, which led to the discharge of a large volume of sediment and water from catchments on the eastern slope of the northern Hidaka Range. The eight catchments examined in this study are characterized by granitic lithology and late Pleistocene periglacial landforms with weakly cohesive, low-resistance periglacial debris thickly covering the weathered bedrocks. This characteristic of the landscape presumably provided a transport-limited condition where some debris flows were initiated by shallow landslides. As they moved, the debris flows grew larger through mobilization and erosion of sediment in channel beds and sidewalls. This sediment mobilization and erosion continued for an extensive distance along the course of the river. Morphological changes induced by channel aggradation and bank erosion were considerable and distinctive from upstream to downstream. Granitic periglacial sediments are amply present on the mountain slopes, river channels, and river banks in the area, likely due to the rarity of intensive rainfall events. These distinctive features of fossil periglacial catchments are important for disaster prevention and catchment-scale sediment management in sub-boreal areas, particularly in the context of climate change, which may generate more frequent and intensive rainfall events.     

Monitoring Heat Losses Using Landsat ETM + Thermal Infrared Data: a Case Study in Unzen Geothermal Field, Kyushu, Japan

The Unzen geothermal field, our study area, is situated in the Shimabara Peninsula of Kyushu Island in Japan and is an area of active fumaroles.. Our prime objectives were (1) to estimate radiative heat flux (RHF), (2) to calculate approximately the heat discharge rate (HDR) using the relationship of RHF with the total heat loss derived from two geothermal field studies, and (3) finally, to monitor RHF as well as HDR in our study area using seven sets of Landsat 7 ETM + images from 2000 to 2009. We used the normalized differential vegetation index (NDVI) method for spectral emissivity estimation, the mono-window algorithm for land surface temperature (LST), and the Stefan–Boltzmann equation analyzing those satellite TIR images for RHF. We estimated that the maximum RHF was about 251 W/m² in 2005 and minimum was about 27 W/m² in 2001. The highest total RHF was about 39.1 MW in 2005 and lowest was about 12 MW in 2001 in our study region. We discovered that the estimated RHF was about 15.7 % of HDR from our studies. We applied this percentage to estimate HDR in Unzen geothermal area. The monitoring results showed a single fold trend of HDR from 2000 to 2009 with highest about 252 MW in 2005 and lowest about 78 MW in 2001. In conclusion, TIR remote sensing is thought as the best option for monitoring heat losses from fumaroles with high efficiency and low cost.     

井-地与井间电位技术联合数值模拟研究剩余油分布(英文)

电法测井有很高的分辨率,但是它的探测半径仅限于井孔周围;井-地电位技术虽然可以探测到足够大的范围,但是它的分辨率却受到很大的限制,特别是对于油水分布或者结构复杂的储层。本文试图通过井-地电位技术和井间电位技术的联合来研究地下储层油水分布范围。具体方法是,采用井-地电位技术研究油水分布在在横向上的展布情况,利用井间电位技术研究油水储层在垂向上的分布,然后采用井间电位结果标定井地电位结果,两者结合提高纵向分辨率,从而确定剩余油的三维空间分布。研究中通过研究注水初期数值模拟结果与水淹期数值模拟结果之差,求取剩余油分布范围。有限差分方法数值模拟表明:井-地电位技术与井间电位技术联合方法可以有效地确定剩余油分布。     

Along-coast shifts of plankton blooms driven by riverine inputs of nutrients and fresh water onto the coastal shelf: a model simulation

Rivers transport nutrients and suspended sediment matter (SSM) as well as fresh water from land to coastal regions, where the biological productivity is high. In the coastal area, the buoyancy of fresh water leads to the formation of horizontal anticyclonic gyres and vertical circulations, which affect the variation of biological production such as plankton blooms. However, the primary production caused by the 3-D dynamics have not been quantitatively discussed, and observations can hardly capture the daily temporal variations of phytoplankton blooms. We developed an ocean general circulation model including a simple ecosystem model, to investigate the 3-D and temporal changes in phytoplankton blooms caused by riverine input such as flooding. The distribution patterns of nutrients and phytoplankton differ significantly from that of fresh water. The phytoplankton maxima shift from the downstream (right-hand side of the river mouth) to the upstream regions (left-hand side of the river mouth). The shift that occurs is categorized by the different nitrate origins: (1) river-originated nitrate is dominant in the downstream region; (2) subsurface-originated nitrate is dominant in the upstream region, and is transported by upwelling associated with vertical circulation and horizontal anticyclonic gyre; and (3) regenerated nitrate is dominant in the upstream region. The total primary production in phytoplankton blooms is maintained not only by river-originated nitrate but also by subsurface-originated nitrate that is 1.5 times larger than the river-originated. Several case studies (e.g., including SSM) were conducted in this study.     

Gas hydrate saturation at Site C0002, IODP Expeditions 314 and 315, in the Kumano Basin,Nankai trough

The degree of gas hydrate saturation at Integrated Ocean Drilling Program (IODP) Site C0002 in the Kumano Basin, Nankai Trough, was estimated from logging‐while‐drilling logs and core samples obtained during IODP Expeditions 314 and 315. Sediment porosity data necessary for the calculation of saturation were obtained from both core samples and density logs. Two forms of the Archie equation (‘quick‐look’ and ‘standard’) were used to calculate gas hydrate saturation from two types of electrical resistivity log data (ring resistivity and bit resistivity), and a three‐phase Biot‐type equation was used to calculate gas hydrate saturation from P‐wave velocity log data. The gas hydrate saturation baseline calculated from both resistivity logs ranges from 0% to 35%, and that calculated from the P‐wave velocity log ranges from 0% to 30%. High levels of gas hydrate saturation (>60%) are present as spikes in the ring resistivity log and correspond to the presence of gas hydrate concentrations within sandy layers. At several depths, saturation values obtained from P‐wave velocity data are lower than those obtained from bit resistivity data; this discrepancy is related to the presence of free gas at these depths. Previous research has suggested that gas from deep levels in the Kumano Basin has migrated up‐dip towards the southern and seaward edge of the basin near Site C0002. The high saturation values and presence of free gas at site C0002 suggest that a large gas flux is flowing to the southern and seaward edge of the basin from a deeper and/or more landward part of the Kumano Basin, with the southern edge of the Kumano Basin (the location of site C0002) being the main area of fluid accumulation.     

Relationship between sinking organic matter and minerals in the shallow zone of the western Subarctic Pacific

We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO₃, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.     

Effects of the introduction of rice on evapotranspiration in seasonal wetlands

Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice‐cropping on evapotranspiration in seasonal wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime^?1) and NVF (1.8 mm daytime^?1) were greater than that in UF (1.0 mm daytime^?1). RF and NVF showed a slight difference in seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non‐vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd.