Near-infrared laboratory spectra of solid H2O/CO2 and CH3OH/CO2 ice mixtures

We present near-IR spectra of solid CO₂ in H₂O and CH₃OH, and find they are significantly different from that of pure solid CO₂. Peaks not present in either pure H₂O or pure CO₂ spectra become evident when the two are mixed. First, the putative theoretically forbidden CO₂ (2ν₃) overtone near 2.134 μm (4685 cm⁻¹), that is absent from our spectrum of pure solid CO₂, is prominent in the spectra of H₂O/CO₂=5 and 25 mixtures. Second, a 2.74-μm (3650 cm⁻¹) dangling OH feature of H₂O (and a potentially related peak at 1.89 μm) appear in the spectra of CO₂-H₂O ice mixtures, but are probably not diagnostic of the presence of CO₂. Other CO₂ peaks display shifts in position and increased width because of intermolecular interactions with H₂O. Warming causes some peak positions and profiles in the spectrum of a H₂O/CO₂=5 mixture to take on the appearance of pure CO₂. Absolute strengths for absorptions of CO₂ in solid H₂O are estimated. Similar results are observed for CO₂ in solid CH₃OH. Since the CO₂ (2ν₃) overtone near 2.134 μm (4685 cm⁻¹) is not present in pure CO₂ but prominent in mixtures, it may be a good observational (spectral) indicator of whether solid CO₂ is a pure material or intimately mixed with other molecules. These observations may be applicable to Mars polar caps as well as outer Solar System bodies.     

Comment on 'The magnetotelluric phase tensor' by T. Grant Caldwell, Hugh M. Bibby and Colin Brown

We demonstrate a minor inconsistency in the appendix of 'The magnetotelluric phase tensor' by Caldwell et al. that can lead to incorrect results, and provide a simple solution for this problem.     

The dependence of the partitioning of iron and europium between plagioclase and hydrous tonalitic melt on oxygen fugacity

The dependence of iron and europium partitioning between plagioclase and melt on oxygen fugacity was studied in the system SiO₂(Qz)—NaAlSi₃O₈(Ab)—CaAl₂Si₂O₈(An)—H₂O. Experiments were performed at 500 MPa and 850 °C/750 °C under water saturated conditions. The oxygen fugacity was varied in the log f _O2-range from −7.27 to −15.78. To work at the most reducing conditions the classical double-capsule technique was modified. The sample and a C—O—H bearing sensor capsule were placed next to each other within a BN jacket to minimise loss of hydrogen to the vessel atmosphere. By this setup redox conditions slightly more reducing than the FeO—Fe₃O₄ buffer could be maintained even in 96 h runs. Raman spectra showed that the BN was modified by reaction with hydrogen resulting in a low hydrogen permeability. The partition coefficients determined for Eu at 850 °C and 500 MPa vary from 0.095 at conditions of the Cu—Cu₂O buffer to 1.81 at the most reducing conditions (C—O—H sensor). In the same f _O2 interval the partition coefficient for Fe varies from 0.55 at oxidising conditions to 0.08 at the most reducing conditions. The partitioning of Sm, which was added as a reference for a trivalent REE, does not vary with the oxygen fugacity, yielding an average value for D = 0.07. Lowering the temperature to 750 °C for a given f _O2 decreases the partition coefficient of Eu and increases that of Fe. Comparison with published data at 1 atm and at higher temperatures shows that both temperature and composition of the melt have strong effects on the partitioning behaviour. As the change of the partition coefficients in the geologically relevant f _O2 range is quite strong, element partitioning of Eu and Fe might be used to estimate redox conditions for the genesis of igneous rocks. Furthermore, by modelling the partitioning data it is possible to extract information about the redox state of the melt. Resulting ferric-ferrous ratios show significant differences from those predicted by empirical models. Received: 14 October 1998 / Received: 5 March 1999     

A global context for megadroughts in monsoon Asia during the past millennium

Proxy reconstructions of precipitation from central India, north-central China, and southern Vietnam reveal a series of monsoon droughts during the mid 14th–15th centuries that each lasted for several years to decades. These monsoon megadroughts have no analog during the instrumental period. They occurred in the context of widespread thermal and hydrologic climate anomalies marking the onset of the Little Ice Age (LIA) and appear to have played a major role in shaping significant regional societal changes at that time. New tree ring-width based reconstructions of monsoon variability suggest episodic and widespread reoccurrences of monsoon megadroughts continued throughout the LIA. Although the El-Niño Southern Oscillation (ENSO) plays an important role in monsoon variability, there is no conclusive evidence to suggest that these megadroughts were associated with anomalous sea surface temperature anomalies that were solely the result of ENSO-like variability in the tropical Pacific. Instead, the causative mechanisms of these megadroughts may reside in protracted changes in the synoptic-scale monsoon climatology of the Indian Ocean. Today, the intra-seasonal monsoon variability is dominated by ‘active’ and the ‘break’ spells – two distinct oscillatory modes of monsoon that have radically different synoptic scale circulation and precipitation patterns. We suggest that protracted locking of the monsoon into the “break-dominated” mode – a mode that favors reduced precipitation over the Indian sub-continent and SE Asia and enhanced precipitation over the equatorial Indian Ocean, may have caused these exceptional droughts. Impetus for periodic locking of the monsoon into this mode may have been provided by cooler temperatures at the extratropical latitudes in the Northern Hemisphere which forced the mean position of the Inter-Tropical Convergence Zone (ITCZ) further southward in the Indian Ocean.     

阿拉斯加输油管的设计和施工方式方案变更过程及其背后的原因和哲学思想

阿拉斯加输油管道公司曾经研发和使用了3种主要施工方案和技术:传统地埋式、特殊埋设和地上敷设方式.在传统地埋式施工方案中,管顶埋深变化于0.9~2.7 m.这主要是考虑了地形变化,而不是沿途的岩性和土壤类型.在特殊埋设方案中,在原油管道必须埋设的地段,如大规模动物迁徙常用地段则使用通道冷液循环降(保)温系统和(或)热管(桩)降(保)温,来保护多年冻土.地上敷设方案包括桩基架设和地上洁净砾石管堤(垫护层).后者只在管道进入和离开多年冻土时采用.架设桩基横梁方案中使用有或没有热管保温的垂直支架梁(单元)(VSM).在初步规划和设计阶段,管道的业主公司(即横穿阿拉斯加管道系统,或TAPS)和随后的阿拉斯加管道服务公司(APSC)不容商量的坚决要求100%的埋设方案.但是,随着勘察工作的进展和设计方案的细化,施工设计方案在不断变化.1977年管道施工结束时,只有57%的管道采用了埋设方式.管道运行30 a后的今天(考虑运行期间维护中所产生的问题),很多经验丰富的工程师认为53%的埋设可能更合理.设计和施工方案变更的原因主要有:1)为了获得通过联邦政府所属的土地所需的许可证,政府有特殊的规定和要求;2)管道公司的设计、施工和管理人员进行了现场野外调查、研究,并积极参与了详细设计和研发;3)美国环境政策法案(NEPA)的最新要求(启用了核准制).阿拉斯加管道服务公司是7家主要石油公司的服务机构.由于这个项目的巨大规模和所涉及的高昂费用,致使各大石油公司的工程师非同寻常程度的参与.在文章中,笔者论述了与阿拉斯加管道施工有关的阿拉斯加管道服务公司、美国联邦和阿拉斯加州政府相关组织机构的形成历史,管道设计演变过程及其背后的哲学思想,以及阿拉斯加管道工程项目的经验和教训.     

Late pleistocene sedimentation history of the Shirshov Ridge, Bering Sea

The analysis of the lithology, grain-size distribution, clay minerals, and geochemistry of Upper Pleistocene sediments from the submarine Shirshov Ridge (Bering Sea) showed that the main source area was the Yukon-Tanana terrane of Central Alaska. The sedimentary materials were transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong northwestward-flowing sea current. The lithological data revealed several pulses of ice-rafted debris deposition, roughly synchronous with Heinrich events, and periods of weaker bottom-current intensity. Based on the geochemical results, we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. The results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.