南黄海夏秋季纤毛虫等微小型浮游动物丰度和生物量变动及其与沙海蜇旺发的关系

大型水母沙海蜇旺发已成为黄海夏季的一个常见的生态现象。然而,沙海蜇旺发与微小型浮游动物尤其是纤毛虫的相互作用关系依然不明。本研究基于2013年6月(水母旺发初期)、8月和9月(水母旺发期)三个航次的调查,对黄海水母高发的I(33°N)、G(34°N)、E(35°N)断面的表层微小型浮游动物的丰度及生物量分布变化与水母发生关系进行探讨。微型鞭毛虫丰度6月平均丰度和生物量分别为357ind./m L和3.92μg C/L,至8月降为145ind./m L和2.55μg C/L,9月回升至160ind./m L和2.84μg C/L。共鉴定纤毛虫31属64种,三个月份纤毛虫的种类组成差别不大。纤毛虫6月的平均丰度和生物量分别为2282ind./L和8.93μg C/L,至8月降为933ind./L和3.92μg C/L,9月回升至2319ind./L和6.55μg C/L。与丰度和生物量的较大变化不同,纤毛虫6月的平均生产力为12.74μg C/(L·d),8月降至7.39μg C/(L·d),9月略增至7.79μg C/(L·d)。桡足类无节幼体仅见于6月(10.59ind./L)和8月(8ind./L),在沙海蜇旺发的8月其平均生物量(0.08μg C/L)和生产力(0.032μg C/(L·d))远低于纤毛虫。本研究表明,在南黄海水母发生过程中,纤毛虫在微小型浮游动物的生物量和生产力中占据了主导地位,并受到水母旺发的直接和间接(级联效应)影响。     

云南金顶超大型铅锌矿床沥青Re-Os法测年及地质意义

油气藏与金属矿床在世界许多沉积盆地内共存,油气成藏与金属成矿的动力学关系备受关注。云南兰坪金顶产有中国目前最大铅锌矿床,也是世界上唯一陆相沉积岩容矿、且形成于新生代的超大型铅锌矿床。矿床中常见沥青、重油等有机质,它们的形成早于或晚于铅锌硫化物成矿存在明显分歧,限制了对油气成藏与铅锌成矿关系的认识。本文针对金顶超大型矿区以古新统云龙组含砾砂岩和砂砾岩为主岩铅锌矿石中沥青,开展了Re-Os法同位素测年,获得68±5Ma的等时线年龄(MSWD=9.2,n=6),指示金顶古油气成藏形成于古新世,先于铅锌硫化物大规模成矿;烃类物质具有通过热化学还原硫酸盐提供铅锌成矿所需硫化氢的客观条件;油气成藏与铅锌成矿在云南金顶矿区很可能是一个先后发生的连续地质过程,成藏为成矿奠基,成矿伴随着油气藏的破坏。     

New measures of the orientation of the linear structure in the sunward hemisphere of the coma of Comet 19P/Borrelly: apparitions of 1994, 2001, and 2008

The sky‐projected orientation (position angle) of the axis (line of maximum density or maximum brightness) of the long time‐known, linear structure (LS) in the sunward hemisphere of the coma of Comet 19P/Borrelly is measured on 45 photographs taken by different observers under different projection conditions and covering three consecutive apparitions (1994, 2001, and 2008) for a total time interval of 5174 days. The analysis of the results by a tomographic approach yields an LS axis constantly oriented towards a fixed point in the space, at Right Ascension 214°.4 ± 0°.5 and Declination –7°.0 ± 0°.5 (J2000), corresponding to an obliquity of 103°.5 ± 1° and an orbital longitude of 147°.2 ± 1°, throughout the relevant interval. Such coordinates are close to the ones found by other authors for the spatial orientation of the nucleus spin axis during the apparitions of 1994 and 2001. In the hypothesis of an LS orientation aligned with the nucleus spin axis, the new results confirm the previous ones and show that this orientation remained unchanged during the subsequent 2008 apparition (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

红团簇巨星的绝对星等及其在天体测距方面的应用

红团簇巨星(red clump giant)是正处于中心氦燃烧阶段的小质量恒星,它们在赫罗图上成团出现且光度弥散很小,因此很容易被辨认出来。理论和观测研究均表明它们具有大致相同的光度,某些波段的光度与金属丰度以及年龄的关系很微弱,可以作为理想的"标准烛光"来测量天体的距离。依巴谷(Hipparcos)天体测量卫星的数据释放后,红团簇巨星被广泛地用于研究银河系结构以及测定本星系群成员的距离。     

一种新的错时相沉积物——巨鲕及其环境意义

华南下三叠统缓坡背景的地层中广泛发育高能滩相鲕粒灰岩,其中含相当数量的巨鲕,粒径大部分在2~6 mm之间,最大可达12 mm。巨鲕的核心类型以多晶粒状方解石和球粒为主,具明暗相间的同心纹层,沿切线方向定向排列的晶体结构表明其原生矿物可能为文石。含巨鲕灰岩与生物碎屑灰岩交互沉积,指示了当时海平面的相对变化。巨鲕在新元古代地层中广泛发育,但在显生宙和现代海洋环镜中超过5 mm的鲕粒相当少见。巨鲕在二叠纪末灭绝事件后大量出现,随着中三叠世生态的复苏、海洋环境趋于正常而又消失。这些特征说明巨鲕可以作为一种错时相沉积物,它的形成无疑与当时的生态和海水环境有关,代表着一类特殊的沉积学现象。分析了巨鲕产出背景、微观结构和沉积特征,对于了解其成因、探索二叠纪—三叠纪之交地质突变期异常的生态状况和特殊的海洋环境具有重要意义。     

Evidence for cometary bombardment episodes

Evidence is found that large terrestrial impacts tend to cluster in discrete episodes, with characteristic separations 25–30 Myr and durations of about 1–2 Myr. The largest impactors are strongly concentrated within such events, and the Cretaceous–Tertiary extinctions occurred within one of them. The evidence also indicates the presence of a weak periodicity, which might be ∼24, ∼35 or ∼42 Myr depending on which peaks are taken as harmonics. The periodicity is most easily explained as a result of the action of the Galactic tide on the Oort comet cloud. The two longer period solutions are consistent with Galactic density estimates and with the current passage of the Solar system through the plane of the Galaxy. Other episodes may be a result of sporadic encounters with spiral arms, nebulae or stars.     

Suprathermal chemical reactions driven by fast hydrogen atoms in cometary comae

We have investigated the role that energetic hydrogen atoms, produced in cometary comae by the photodissociation of water molecules, could have in driving chemical reactions that are endothermic, or possess activation energy barriers. We have developed a model of the density and energy spectrum of these atoms in the coma and have incorporated a number of reactions driven by fast H atoms into our existing coma model. We find that, in high-activity comets close to the Sun, such reactions are competitive with direct photodissociation as the principal destruction mechanism for molecules with long lifetimes in the solar radiation field. We show that measurements of the CH₂OH : CH₃O ratio may be used to assess the importance of suprathermal reactions in the coma. We also confirm that these reactions are probably unable to account for the observed HNC : HCN ratios.     

The Changes of the Orbital Elements and Estimation of the Initial Velocities of Stream Meteoroids Ejected from Comets and Asteroids

The values of the initial velocity of the meteoroids ejected from the parent bodies are small and as a result, the most of the young meteoroid streams have similar orbits to their parent bodies. Assuming that the members of the observed meteor stream evolved under the influence of gravitational perturbations mostly, Pittich [1991, Proceedings of the Conference on Dynamic of Small Bodies of the Solar System, Polish-Slovak Conference, Warsaw, October 25–28, 1988, pp. 55-61], Williams [1996, Earth, Moon, Planets 72, 321–326; 2001, Proceedings of the Meteoroids 2001 conference, Kiruna, Sweden, August 6–10, 2001, pp. 33–42] estimated the ejection velocities of the stream meteoroids. Equation relating the ejection velocity Δυ and the change Δa of the semi-major axis, Williams (2001), was applied with two slightly different variations. In the first one (M1) as Δa the difference between the mean orbit of the stream and the orbit of the parent body was substituted, in the second one (M2), as Δa the dispersion of semi-major axes around the mean orbit of the stream was used. The results obtained by these two methods are not free from discrepancies, partly explained by the particular orbital structure of the stream. Kresak [1992, Contrib. Astron. Obs. Skalnate Pleso 22, 123–130] strongly criticized the attempts to determine the initial velocities of the stream using the statistics of the meteor orbits. He argued that this is essentially impossible, because the dispersion of the initial velocities are masked by much larger measuring errors and by the accumulated effects of planetary perturbations. In our paper, we study the reliability of M1 and M2 methods. We made a numerical experiment consisting of formation of several meteor streams and their dynamical evolution over 5000 years. We ejected meteoroids particles from the comets: 1P/Halley, 2P/Encke, 55P/Tempel-Tuttle, 109P/Swift-Tuttle and from minor planets (3200) Phaethon and 2002 SY₅₀. During the integration, the ejection velocities were estimated using both M1 and M2 methods. The results show that the velocities obtained by M1 method are unstable: too high or too low, when compared with the known ejection velocities at the time of the stream formation. On the other hand, the velocities obtained using M2 method are too small, mostly. In principle, M2 estimates the dispersion of the distribution of the ejection velocities around the mean value, not the mean value itself. Applying more accurate Equation relating Δυ and Δa we decreased the bias of the results, but not their variation observed during the evolution of the streams and the parent bodies. We have found that the variability of the estimated ejection velocities was caused mainly by the gravitational changes of the semi-major axis and eccentricity of the parent body. In brief, we have found that the reliability of the results obtained by M1 or M2 method are low, and have to be used with great care.     

Vilnius Photometry of Red Giant Stars in the Open Cluster NGC 7789

Photoelectric Vilnius seven-color photometry is presented and analyzed for a sample of 24 red giant branch and clump stars in the open cluster NGC 7789. For each star we have determined photometric spectral type, absolute magnitude, interstellar reddening, effective temperature, metallicity, and surface gravity. From averages over the stars in the sample we find the mean reddening to the cluster E _Y−V = 0.21± 0.02 (s.d.), or E _B−V = 0.25, and the apparent distance modulus (m−M) _V = 12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The mean overall metallicity is found to be [Fe/H] = −0.18± 0.09 (s.d.). The clump stars, on average, appear to be slightly more metal-rich than the other red giants, which is most probably caused by evolutionary changes of carbon and nitrogen molecular bands falling in the photometric passbands. A difference in mass between the two groups of stars has also been detected, which suggests that the clump stars might have undergone extra mass loss before reaching their core He-burning phase of evolution.