Holocene paleoenvironmental changes inferred from diatom assemblages in sediments of Kusawa Lake, Yukon Territory, Canada

The southwest Yukon Territory, Canada, is an important region for recovering sensitive records of Holocene paleoclimatic change. More information is needed, however, to constrain the timing of the major Holocene climatic transitions, and to understand associated impacts on different ecosystems. For example, paleolimnological studies have focused on small lakes and ponds, but the history of large lakes has received little study. We analyzed diatom assemblages, species richness, valve concentrations, and biogenic silica, in the sediments of Kusawa Lake (60°16.5'N; 136°10.9'W; 671 m a.s.l.) to reconstruct the responses of this large (surface area = 142 km²), deep (Z_max = 135 m) freshwater ecosystem to Holocene climatic transitions. Diatoms colonized the lake soon after ice retreat, around 11,000 cal yr BP; assemblages throughout the record were dominated by planktonic types. Diatom concentrations and biogenic silica were high during the Holocene Thermal Maximum between 10,700 and 7300 cal yr BP, then began to decrease in response to cooling associated with orbitally driven reductions in insolation. Diatom assemblages shifted towards taxa with lower surface water temperature optima after 8300 cal yr BP, perhaps in response to abrupt and progressive cooling. Our study confirms that diatom assemblages in large lakes are sensitive to regional-scale paleoclimatic changes.     

Estimates of monoterpene and isoprene emissions from the forests in Switzerland

Emission rates of biogenic volatile organic compounds emitted by the forests were estimated for five geographical regions as well as for all Switzerland. Monoterpene and isoprene emissions rates were calculated for each main tree species separately using the relevant parameters such as temperature, light intensity and leaf biomass density. Biogenic emissions from the forests were found to be about 23% of the total annual VOC emissions (anthropogenic and biogenic) in Switzerland. The highest emissions are in July and lowest in January. Calculations showed that the coniferous trees are the main sources of the biogenic emissions. The major contribution comes from the Norway spruce (picea abies) forests due to their abundance and high leaf biomass density. Although broad-leaved forests cover 27% of all the forests in Switzerland, their contribution to the biogenic emissions is only 3%. Monoterpenes are the main species emitted, whereas only 3% is released as isoprene. The highest emission rates of biogenic VOC are estimated to be in the region of the Alps which has the largest forest coverage in Switzerland and the major part of these forests consists of Norway spruce. The total annual biogenic VOC emission rate of 87 ktonnes y^–1 coming from the forests is significantly higher than those from other studies where calculations were carried out by classifying the forests as deciduous and coniferous. The difference is attributed to the high leaf biomass densities of Norway spruce and fir (abies alba) trees which have a strong effect on the results when speciation of trees is taken into account. Besides the annual rate, emission rates were calculated for a specific period during July 4–6, 1991 when a photochemical smog episode was investigated in the Swiss field experiment POLLUMET. Emission rates estimated for that period agree well with those calculated for July using the average temperatures over the last 10 years.     

The establishment of the atmospheric emission inventories of the ESCOMPTE program

Within the frame of the ESCOMPTE program, a spatial emission inventory and an emission database aimed at tropospheric photochemistry intercomparison modeling has been developed under the scientific supervision of the LPCA with the help of the regional coordination of Air Quality network AIRMARAIX. This inventory has been established for all categories of sources (stationary, mobile and biogenic sources) over a domain of 19,600 km² centered on the cities of Marseilles–Aix-en-Provence in the southeastern part of France with a spatial resolution of 1 km². A yearly inventory for 1999 has been established, and hourly emission inventories for 23 days of June and July 2000 and 2001, corresponding to the intensive measurement periods, have been produced. The 104 chemical species in the inventory have been selected to be relevant with respect to photochemistry modeling according to available data. The entire list of species in the inventory numbers 216 which will allow other future applications of this database. This database is presently the most detailed and complete regional emission database in France. In addition, the database structure and the emission calculation modules have been designed to ensure a better sustainability and upgradeability, being provided with appropriate maintenance software. The general organization and method is summarized and the results obtained for both yearly and hourly emissions are detailed and discussed. Some comparisons have been performed with the existing results in this region to ensure the congruency of the results. This leads to confirm the relevance and the consistency of the ESCOMPTE emission inventory.     

南海北部一百万年以来的表层古生产力变化：来自ODP1144站的蛋白石记录

通过南海北部ODP 1144站蛋白石含量测定及其堆积速率的计算,并结合氧同位素记录等相关资料,获得南海北部1050ka以来高分辨率的表层古生产力变化与冰期旋回和东亚季风的关系。约900ka以来,蛋白石含量及其堆积速率较900ka以前明显增加,反映了“中更新世革命”事件之后,全球气候变冷,并导致表层生产力的提高。由于第四纪冰期旋回中的冬、夏季风的加强,加上1144站特殊的地理位置,使该站在冰期时表层生产力增加,间冰期时表层生产力降低。浮游有孔虫氧同位素记录与蛋白石含量及其堆积速率的时间序列频谱分析结果显示,三者均出现了相对应的偏心率周期、斜率周期和岁差周期,说明该站表层生产力的变化主要受地球轨道周期的驱动。     

生物胺对锯缘青蟹大颚器发育的调节作用

雌性锯缘青蟹(Scylla serrata)于实验的第1天、第5天、第10天，分别注射100μL剂量为1μg／g体质量的5-HT，OA和DA，第15天解剖。结果表明，5-HT对锯缘青蟹大颚器发育具有显的促进作用，OA和DA的作用不明显。经免疫细胞化学检测，大颚器内存在5-HT免疫阳性细胞，免疫阳性细胞多数为卵圆形，少数具有很长的胞突，该结果首次为5-HT参与大颚器的生理活动提供了形态学证据。     

A Study of Pretreatment Methods for Terrigenous Grain-Size Analysis of Marine Sediments

The prerequisite for obtaining variations of terrigenous grain-size of marine sediments is how to effectively remove non-terrigenous matters and preserve terrigenous particles synchronously. Combined with observations under biological microscope and scanning electron microscope, a comparative study of biogenic debris removal effect and terrigenous grain-size analysis under different pretreatment condition was performed on core sediments, which were retrieved in the South China Sea during the MD190 cruise. Our new results showed that the main three biogenic particles, namely, organic matter, carbonate, and opal in marine sediments could be removed effectively by 30% H₂O₂ in a stirring water bath at 60 ℃ for 3 h, 0.5% HCl for 1 h, and 2 mol/L Na₂CO₃ in a stirring water bath at 85 ℃ for 5 h, in turn. Such pretreatments achieved the goals of biogenic debris removal efficiency and relatively well-preserved terrigenous particles. Prior to selecting an appropriate pretreatment method, this study suggested that the actual effects of biogenic detritus on grain-size results of diverse marine sediment samples should be taken into account. If the laboratory data are ensured to be closer to the natural grain-size distribution of terrigenous particles, the removals of all biogenic debris are not always needed, and the less pretreatment processes the better. For example, opal particles have little effect on terrigenous grain-size distribution when their percentage is lower than 2%. Thus, there is no use to remove them from marine sediments before laboratory grain-size analysis of terrigenous particles. Additionally, ultrasonic is not suggested through the whole process of terrigenous grain-size analysis because the strong energy of ultrasonic can lead to the fragmentation of some fragile terrigenous particles.     

Biogenic signature and ultra microfossils in ferromanganese nodules of the Central Indian Ocean Basin

Theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts (1) chemical oxidation (abiotic origin) and (2) deposition of the metals through microbial enzymatic processes (biogenic origin). One of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes. However, well-documented literature in this regard is either lacking or very scanty in case of Indian Ocean nodules. Using high resolution FEG-SEM we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from Central Indian Ocean Basin (CIOB) that are presented in this paper. The microfossils are mostly protozoans belonging to varieties of bacteria, diatoms and foraminifera. Some of the features recorded in this study have perhaps never been reported before from any manganese nodules. The chemical compositions of these ultra microfossils indicate a high-level of manganese precipitation in and around them in comparison to the distant surrounding areas. While clumpy microbes are enriched with nickel, the rod shaped bacteria are rich in copper. Up to 4.70 wt.% nickel and 5.31 wt.% Cu have been recorded in the fossilized microbe bodies. The high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the CIOB.     

试论火山岩油气藏成藏机理

全球100多个国家/地区在火山岩内或其周围发现了油气藏或油气显示,展示了火山岩油气藏勘探的广阔前景。火山岩已从油气勘探的"禁区"转变为了"靶区",成为油气勘探的新目标。火山岩储集物性较好,其本身可直接作为储层,各类侵入体与围岩相互作用还可形成与火成岩有关的圈闭。火山岩油气藏的烃源包括有机成因和无机成因两种。火山作用可以明显提高烃源岩内有机质的成熟度,加快烃的产生,促进油气运移,并为无机成因烃提供合成原料(CO_2和H_2等)和运移通道。虽然火山岩在盆地早期尤为发育,约占盆地充填体积的1/4,但是目前火山岩油气储量仅占世界油气探明储量的1%左右,勘探潜力巨大。中国沉积盆地内发育不同时代火山岩,火山岩储层与烃源岩匹配较好,无机成因气来源丰富,火山岩油气藏正在成为我国油气勘探的重要领域之一。     

Paleolimnological evidence of the response of the central Canadian treeline zone to radiative forcing and hemispheric patterns of temperature change over the past 2000 years

Instrumental climate records from the central Canadian treeline zone display a pattern of variation similar to general Northern Hemisphere temperature trends. To examine whether this general correspondence extends back beyond the instrumental record, we obtained a sediment core from Lake S41, a small lake in the Northwest Territories of Canada at 63°43.11′ N, 109°19.07′ W. A radiocarbon-based chronology was developed for the core. The sediments were analyzed for organic-matter content by loss-on-ignition (LOI), biogenic-silica content (BSi), and chironomid community composition to reconstruct July air temperature and summer water temperature. The paleolimnological records were compared with records of atmospheric CO₂ concentration, solar variability, and hemispheric temperature variations over the past 2000 years. The results of the analyses suggest that widely-documented long-term variations in Northern Hemisphere temperature associated with radiative forcing, namely the cooling following the medieval period during the Little Ice Age (LIA), and twentieth century warming, are represented in the central Canadian treeline zone. There is also evidence of a brief episode of warming during the eighteenth century. As evidenced by LOI and BSi, the twentieth century warming is typified by increased lake productivity relative to the LIA. Depending upon the measure, the increased productivity of the twentieth century nearly equals or exceeds that of any other period in the past 2000 years. In contrast, the rate of chironomid head capsule accumulation decreased and remained low during the twentieth century. Although the chironomid-inferred temperature reconstructions indicate cooling during the LIA, they present no evidence of greatly increased temperatures during the twentieth century. Warming during the twentieth century might have enhanced lake stratification, and the response of the chironomid fauna to warming was attenuated by decreased oxygen and lower temperatures in the hypolimnion of the more stratification-prone lake.

The effects of organic removal treatment on the integrity of δ<Superscript>18</Superscript>O measurements from biogenic silica

Prior to oxygen isotope analysis of biogenic silica by fluorination techniques, sediments must be cleaned of all organic compounds. Despite the expanding volume of research utilising oxygen isotope ratios in biogenic silica in palaeoclimatology, very little is known about the effects of different standard preparation methods for the removal of organic matter on the isotope values. Here we compare a number of methods for the removal of organic matter in order to assess their effectiveness and influence on subsequent isotope measurements. Not all the methods described here effectively removed organic matter, the best treatments were H₂O₂ and ignition in air at 550°C. Ignition in air at 950°C, and heating in vacuum at 250 and 450°C results in marked alteration of isotope values, whereas use of hydrogen peroxide (H₂O₂), nitric acid (HNO₃) and plasma ashing have little or no effect, within the bounds of analytical error. Ignition in air at 550°C was the most effective technique, and induced no alteration of δ¹⁸O_silica, but practical constraints may limit the application of this method routinely. Our findings indicate that considerable caution is required when preparing sediment for isotope analysis of biogenic silica.