中国南极球粒陨石的高精度钾同位素研究

钾和其他中等挥发性元素亏损是类地行星普遍的全岩化学成分特征之一,能用来示踪不同的亏损过程。球粒陨石是组成行星的前体物质,研究球粒陨石中钾同位素的亏损和分异机制,对于太阳系物质或行星的起源、形成和演化具有十分重要的意义。本文利用近年来发展的高精度钾同位素分析技术,测试了14个中国南极陨石以及6个目击型陨石(Murchison、Allende、Ningqiang、Tagish Lake、Xinyang和Banma)的全岩钾同位素组成。结果显示,21个碳质球粒陨石全岩δ⁴¹K值分布范围为-0.62‰±0.05‰至0.37‰±0.08‰,平均值为-0.32‰±0.24‰(2SD),比全岩硅酸盐地球(BSE)稍重。18个普通球粒陨石全岩数据(如果异常值GRV 021603除外)的δ⁴¹K值分布范围为-1.02‰±0.05‰到-0.61‰±0.02‰,平均δ⁴¹K值为-0.81‰±0.15‰(2SD),比全岩硅酸盐地球稍轻。2个目击型陨石Murchison(CM2型)和Allende(CV3型),呈现较大的内部钾同位素差异(分别为0...     

南极格罗夫山普通球粒陨石的矿物岩石学特征

本文研究了第19次中国南极科学考察队收集的97块普通球粒陨石样品的矿物岩石学特征,在此基础上划分了陨石的岩石学类型、化学群、冲击变质和风化类型。共发现5块非平衡型普通球粒陨石:GRV 020011(L3),GRV 020035(H3),GRV 020054(H3),GRV 020137(L3)和GRV020169(L3)。化学群分类的结果是H群陨石24块,L群70块,LL群3块。多数样品的冲击变质程度较低,但也有少量样品具有S5型的冲击变质特征。样品的风化程度普遍较低,仅GRV020055(H5),GRV022123(L5)和GRV022462(LL6)3块陨石达到了W3型。     

GIS for the assessment of the groundwater recharge potential zone

Water resources in Taiwan are unevenly distributed in spatial and temporal domains. Effectively utilizing the water resources is an imperative task due to climate change. At present, groundwater contributes 34% of the total annual water supply and is an important fresh water resource. However, over-exploitation has decreased groundwater availability and has led to land subsidence. Assessing the potential zone of groundwater recharge is extremely important for the protection of water quality and the management of groundwater systems. The Chih-Pen Creek basin in eastern Taiwan is examined in this study to assess its groundwater resources potential. Remote sensing and the geographical information system (GIS) are used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The weights of factors contributing to the groundwater recharge are derived using aerial photos, geology maps, a land use database, and field verification. The resultant map of the groundwater potential zone demonstrates that the highest recharge potential area is located towards the downstream regions in the basin because of the high infiltration rates caused by gravelly sand and agricultural land use in these regions. In contrast, the least effective recharge potential area is in upstream regions due to the low infiltration of limestone.     

Polycyclic aromatic hydrocarbons in surface sediments of the East China Sea and their relationship with carbonaceous materials

This study measured concentrations of polycyclic aromatic hydrocarbons (PAHs) in surface sediments in the East China Sea (ECS) to investigate possible sources and fate of PAHs. Total concentration of PAHs in the sediments of the ECS ranged from 22 to 244 ng g(-1), with the highest levels in the coastal area and outer shelf. The observed PAH results showed elevated levels in both inner and outer shelf areas, a finding that is different from predictions by an ocean circulation model, suggesting that terrestrial sources are important for PAH contaminations in the ECS, while sediment resuspension, tidal changes and lateral transport may be important in affecting the distribution of PAHs in the outer shelf. The distribution of PAHs in the surface sediments of the ECS is similar to the distribution of carbonaceous materials (e.g., particulate organic carbon and black carbon), suggesting that carbonaceous materials may strongly affect the distribution of PAHs.     

Evaluation of dam overtopping probability induced by flood and wind

This study develops a probability-based methodology to evaluate dam overtopping probability that accounts for the uncertainties arising from wind speed and peak flood. A wind speed frequency model and flood frequency analysis, including various distribution types and uncertainties in their parameters, are presented. Furthermore, dam overtopping probabilities based on monthly maximum (MMax) series models are compared with those of the annual maximum (AMax) series models. An efficient sampling scheme, which is a combination of importance sampling (IS) and Latin Hypercube sampling (LHS) methods, is proposed to generate samples of peak flow rate and wind speed especially for rare events. Reservoir routing, which incorporates operation rules, wind setup, and run-up, is used to evaluate dam overtopping probability.     

Seasonal evolution of the intraseasonal variability of China summer precipitation

Climate Dynamics - Seasonal cycle of China summer precipitation has significant impacts on its subseasonal predictability; yet current understanding of seasonal evolution of the intraseasonal...     

Analysis of the Sanchung inundation during Typhoon Aere, 2004

Typhoon Aere swept over Taiwan with heavy rain, which induced huge discharge in the Danshuei River in August 2004. The flood in the Danshuei River intruded Sanchung through a culvert that was under construction. The deluge inundated thousands of premises and resulted in severe damage. This study reconstructs the event scenario using hydrologic and hydraulic methods to analyse the causes of the disaster. We integrated the radar rainfall estimations and rain gauge observations to recreate the temporal and spatial varied precipitation inputs; estimated the influent volume from the culvert using hydrologic equations; and simulated the flood dynamic within the study area during the event with a coupled overland and sewer flow model. The evidence showed that both the rainfall and the culvert flow contributed similar flood volume to the study area, but culvert discharge concentrated at single location within short time period such that the local drainage system could not cope with and notable damage was incurred.     

Milankovitch-scale environmental variation in the Banda Sea over the past 820 ka: Fluctuation of the Indonesian Throughflow intensity

We describe the environmental variation in the Banda Sea over the past 820 ka by using the magnetic parameters and oxygen isotope data from the core MD012380. Overall, characteristics of the magnetic parameters show simultaneous variation with marine isotope stage (MIS), especially in the last 420 ka. There are fewer, coarser and more oxidative magnetic minerals in glacial periods, and turn to opposite conditions in interglacial periods. Spectral results clearly present the Milankovitch periods over the last 820 ka, especially the eccentricity period (400-ka and 100-ka). However, the magnetic data shows different pattern before and after 420 ka. Thus, we segmented the time-series data into two periods: MIS 20 to MIS 12 and MIS 11 to MIS 1. During MIS 20 to MIS 12, the spectra of magnetic data show clear periods related to the obliquity (41-ka) and precession (23-ka and 19-ka), while they present only the eccentricity period (100-ka) during MIS 11 to MIS 1. This feature, which splits the late Pleistocene at around 420 ka, could be attributed to the mid-Brunhes event (MBE). In the Banda Sea, main factor controlling the variation of the magnetic minerals is considered as the fluctuation of the Indonesian Throughflow (ITF) intensity due to sea-level change. Thus, the magnetic data show clear 400-ka and 100-ka periods (main MIS cycle). Besides, the eccentricity signals are relatively dominant in the last ～420 ka, implying that the ITF might become more important after the MBE in the Banda Sea.     

A note on the derivation of wave action balance equation in frequency space

In this paper the wave action balance equation in terms of frequency-direction spectrum is derived.A theoretical formulation is presented to generate an invariant frequency space to replace the varying wavenumber space through a Jacobian transformation in the wave action balance equation.The physical properties of the Jacobian incorporating the effects of water depths are discussed.The results provide a theoretical basis of wave action balance equations and ensure that the wave balance equations used in the SWAN or other numerical models are correct.It should be noted that the Jacobian is omitted in the wave action balance equations which are identical to a conventional action balance equation.