Contribution to the atmospheric NH3 budget

The paper deals with recent measurements of NH₃ applying an improved Indophenolblue method after Bertheolot. Aircraft measurements show a marked difference of the absolute concentration of NH₃ between summer and winter. This seasonal difference indicates the effectiveness of biogenic NH₃ sources during the summer months. Quantitative analysis of the source strength of different soils show the influence of the temperature at the ground and of the pH-value of the soil. The main sources of NH₃ are continental, but microbiological activity in the soil alone cannot fully explain the NH₃ flux into the atmosphere.     

Temporal dynamics and productivity of biogenic soil crusts in the central Karakum desert, Turkmenistan

Biogenic soil crusts (BSCs), consisting of different combinations of mosses, lichens, liverworts, fungi and cyanobacteria, are a widespread phenomenon in arid and semi-arid environments. BSCs are found throughout those areas unaffected by grazing and other anthropogenic activities. Current economic conditions in the newly Independent Central Asian States favor the development of BSCs, which may significantly influence plant communities. The data from 40-years of field observations in a protected area in the Karakum Desert, Turkmenistan, together with a sequence of aerial photographs of the same area may contribute to the study of the establishment of BSCs and understanding their role in vegetation communities. The fenced-off Karrykul area can serve as a model for the current processes in the vast desert areas in Central Asia, which are underused due to the financial constraints. It is hypothesized that after some 15 years, the role of BSCs changes from a positive (rehabilitating) effect on the first stages of protection, to a negative effect on the structure and biomass of vegetation communities. Therefore, undergrazing, as well as overgrazing, should be considered as a desertification factor.     

Competition between enzymatic and abiotic reduction of uranium(VI) under iron reducing conditions

Reduction of U(VI) under iron reducing conditions was studied in a model system containing the dissimilatory metal-reducing bacterium Shewanella putrefaciens and colloidal hematite. We focused on the competition between direct enzymatic uranium reduction and abiotic reduction of U(VI) by Fe(II), catalyzed by the hematite surface, at relatively low U(VI) concentrations (< 0.5 μM) compared to the concentrations of ferric iron (> 10 mM). Under these conditions surface catalyzed reduction by Fe(II), which was produced by dissimilatory iron reduction, was the dominant pathway for uranium reduction. Reduction kinetics of U(VI) were identical to those in abiotic controls to which soluble Fe(II) was added. Strong adsorption of U(VI) at the hematite surface apparently favored the abiotic pathway by reducing the availability of U(VI) to the bacteria. In control experiments, lacking either hematite or bacteria, the addition of 45 mM dissolved bicarbonate markedly slowed down U(VI) reduction. The inhibition of enzymatic U(VI) reduction and abiotic, surface catalyzed U(VI) reduction by the bicarbonate amendments is consistent with the formation of aqueous uranyl-carbonate complexes. Surprisingly, however, more U(VI) was reduced when dissolved bicarbonate was added to experimental systems containing both bacteria and hematite. The enhanced U(VI) reduction was attributed to the formation of magnetite, which was observed in experiments. Biogenic magnetite produced as a result of dissimilatory iron reduction may be an important agent of uranium immobilization in natural environments.     

Diatom Paleolimnological Record of Holocene Climatic and Environmental Change in the Altai Mountains, Siberia

The sedimentary diatom records of three shallow lakes in the Altai Mountains, southern Siberia, were examined to assess the nature and timing of Holocene environmental changes. Few paleoenvironmental records, especially reconstructions not based on pollen, have been reported from this region. The lakes differ in elevation, annual precipitation, and catchment vegetation. Diatom assemblages in all lakes were dominated for the entire period of record by small benthic species of Pseudostaurosira Williams & Round, Staurosira Ehrenberg, and Staurosirella Williams & Round. Planktonic taxa only occur in very low abundances (<5%). The most diverse diatom flora was found in Dzhangyskol, which is situated at the lowest elevation within a forested catchment. A lack of detailed information on the ecological preferences of the dominant taxa and the complexity of environmental drivers make direct interpretation of the diatom record difficult. However, other proxies suggest that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata in Grusha Ozero reflect millennial-scale variability in climate. Together, chironomids and diatoms provide evidence of a cooling possibly correlative to the Younger Dryas Stade and subsequent early-Holocene warming consistent with pollen evidence of afforestation, which also is likely linked to increased humidity. By ~6000 cal year BP, the transition to a cooler, more continental climate had begun. The diatom record of Akkol shows significantly less variation in diatom community composition, but biogenic silica accumulation rates, a proxy for diatom productivity, appear to reflect climatic variability driven by insolation trends over the past 8000 years. Long-term variability in Dzhangyskol is not clearly linked to climate.     

苏北高压变质带绿片岩中石榴石内文石包裹体的发现

苏北高压变质带位于苏鲁超高压变质带东南缘,露头多为绿片岩相的中—晚元古代云台岩群,典型的蓝片岩仅见于灌云县杨集的钻孔岩心中。本文通过拉曼光谱研究,在连云港地区的绿片岩内石榴石中发现文石(CaCO3)包裹体。文石呈细小包裹体残留于细粒半自形石榴石斑晶中。这些石榴石作为低扩散的刚性矿物,经历了多期变质变形作用,变质反应证据保存在石榴石的成分环带及包体矿物组合中。文石包裹体的存在证明苏北高压变质带北部的、即本区出露的这套岩系是早期经历了高压变质作用、晚期又叠加了绿片岩相变质作用的高压变质地体。     

胶州湾秋季文石饱和度分布及控制因素分析

基于2017-10-18航次在胶州湾调查获取的水文、碳化学和叶绿素a(Chl a)等数据与资料,分析了秋季该海域文石饱和度(Ω_arag(现场))的分布状况,探讨了影响其空间分布的主要控制因素。结果显示,秋季航次期间胶州湾表层Ω_arag(现场)为1.85～2.57,平均值为(2.20±0.24);其分布具有较大的空间差异,低值位于湾的西部和东北部(<2.05),高值位于湾口(>2.45),总体上呈现出由湾口向湾顶逐步降低的趋势。除了通过分析Ω_arag(现场)与温度、盐度和Chl a的相关性来定性确定Ω_arag(现场)的主控因素外,我们还通过引入总碱度与溶解无机碳的差值作为Ω_arag(现场)的指征参数,定量确定了影响Ω_arag(现场)空间分布的主要过程及其贡献。研究发现,陆源输入是影响胶州湾秋季Ω_arag(现场)空间分布的最重要因素(>50%),而温度和生物过程的影响相对较小。     

Potential deposition of biogenic silica source sediment in the Paleo-Yangtze Grand Underwater Delta estimated with satellite remote sensing

Biogenic silica sediment constitutes one of the critical sources of particle income in the oceans. In this paper, satellite remote sensing of primary production, sinking flux, and molar ratio of Si/C were utilized to elucidate potential biogenic silica sediment in the Paleo-Yangtze Grand Underwater Delta. Primary production retrieval showed that daily primary production in the Paleo-Yangtze Grand Delta was 3.3–10.8?Mt?d^?1, with 5.8?Mt?d^?1 on average. Sinking flux, retrieved with in situ observations and satellite remote sensing, was within the range of 109–657?mg?Cm^?2?d^?1, or about 23% of total primary production, on average. A molar ratio of Si/C of 0.11–0.45 interval was used in the area, for the Paleo-Yangtze Grand Delta was similar to coastal water and affected by many factors. Considering that phytoplankton in the Paleo-Yangtze Grand Underwater Delta is mainly diatom (80% on average), about 0.21–0.88 billion tons of biogenic silica source sediment is produced in the area annually. With the reduction of land source sediment occurring in recent years in the area, biogenic silica sediment may be one of the dominant sediment sources for maintaining the future stability of the Paleo-Yangtze Grand Underwater Delta.     

Natural background and anthropogenic inputs of polycyclic aromatic hydrocarbons (PAH) in sediments of South-Western Barents Sea

Polycyclic aromatic hydrocarbons (PAH) were measured in sediment cores from 13 locations in South-Western Barents Sea as part of a detailed study of the Norwegian seabed under the MAREANO program. The generally low PAH levels found, an average around 200 ng g⁻¹ dry weight for sum PAH, indicate low inputs of petroleum hydrocarbons to the marine environment in the area. Differences in PAH composition and various PAH ratios indicate a natural, mostly petrogenic origin of PAH in sediments from the open sea locations, while the fjord locations show higher pyrogenic PAH contents with an increase towards upper sediment layers, indicating low inputs from human activities. Petrogenic PAH levels increase in deeper sediments at open sea locations, also when normalised to total organic carbon (TOC) contents, suggesting natural leakages of oil-related hydrocarbons in the area.     

Occurrence of hydrogen sulfide in the ground water of Kuwait

Hydrogen sulfide occurs in high concentration (10–200 mg/l) in different parts of Kuwait City and its suburbs at relatively shallow depths (15–40 m from the surface). This was revealed by drilling through the aquifer system underlying the city and sampling and analyzing the ground water at the drilled locations. The near-absence of coliform bacteria in the sulfide-rich zones, the presence of sulfur-reducing bacteria in the deep (>80 m) Dammam Formation aquifer and a linear positive relation between the concentration of hydrogen sulfide and the total dissolved solids content suggested non-anthropogenic origin of the sulfide in the ground water of Kuwait. The upward movement of sulfide-rich water from depth and its differential flushing by surface recharge through outcrops of the aquifers appear to have given rise to the present distribution of hydrogen sulfide in the aquifers underlying the Kuwait City.     

Suitability of biogenic carbonate of Lithospermum fruits for C dating

Lithospermum (Boraginaceae) belongs to a small group of plant taxa that accumulate biogenic carbonate in their fruits. In this genus, carbonate incrustations form in the cells of the epidermis and sclerenchyma of the pericarp. Fossil Lithospermum fruits (nutlets) with well-preserved calcified tissues commonly occur in Quaternary sediments and cultural layers. We tested the suitability of biogenic carbonate of Lithospermum fruits for radiocarbon dating using a total of 15 AMS measurement results from four modern and 11 fossil samples. The ¹⁴C data from modern samples suggest that Lithospermum utilises only atmospheric carbon to synthesise calcite in the nutlets. In general, the ages determined through ¹⁴C dating of fossil fruitscorresponded well with the absolute-age intervals for archaeological sites over the last 5000 yr. Biogenic carbonate of Lithospermum fruits, like that of Celtis, represents a new source of chronological information for late Quaternary studies.