黄土高原定西鲁家沟黄土剖面15 ka以来的环境演变

根据鲁家沟黄土剖面粒度、磁化率、有机质和碳酸盐含量等气候代用指标的变化和14C测年结果,分析和讨论了定西地区近15 cal.kaBP以来气候演化的过程。结果表明15 cal.kaBP以来的气候变化可划分为4个阶段:(1)末次冰期晚期(14900~11200 cal.aBP),气候较为寒冷干旱;(2)全新世早期(11200~7560 cal.aBP),气候开始转暖转湿,但整体上较为寒冷;(3)全新世中期(7560~3600 cal.aBP),气候温暖湿润,夏季风强盛;(4)全新世晚期(3600~1200 cal.aBP),气候变得干旱,夏季风强烈减退,风尘堆积旺盛,形成了现代黄土和表土层。该区末次冰期晚期以来的环境变化是不稳定的,气候存在频繁次级波动。1500~1200 cal.aBP的晚全新世期间,有机质含量出现峰值,表明气候总体向干旱化发展的同时,叠加了人类活动的影响。     

南黄海晚更新世以来孢粉记录的古环境变化

依据南黄海DLC70-3孔71.2m长沉积序列的孢粉记录,结合测年数据,有孔虫和粒度等环境指标,恢复了研究区晚更新世以来的古环境变化。钻孔孢粉组合可以反演南黄海陆缘区植被面貌,其中草本花粉在整个剖面占绝对优势,具有超代表性,而木本花粉代表性低。除冰盛期沉积缺失之外,孢粉等指标在MIS5阶段以来变化显著:MIS5和MIS3的亚间冰阶及MIS2/1(冰消期)阶段,阔叶树种和蒿属比例较高,沟鞭藻、有孔虫含量也较高,气候偏暖,属沉积动力相对稳定的浅海或滨海环境;而MIS5及MIS3阶段的亚冰阶和MIS4阶段,针叶组分或冷杉含量增加,中生-水生草本含量相对较高,而有孔虫含量极低或消失,气候偏冷,属沉积动力相对复杂的滨岸湖泊或沼泽等陆相环境。同时,对比周边地区其他孢粉记录,结果表明,在冰期-间冰期旋回过程中孢粉组合中针叶-阔叶组分含量此消彼长,草本含量的相对变化可指示滨岸局域植被的演替,且一定程度上可以反映海平面的升降。     

威海朝阳港潟湖湿地古生物化石特征及其古环境意义

根据孢粉和微体古生物化石特征,分析了朝阳港潟湖中全新世以来的古植被、古气候和古环境演变过程.研究表明,在第1阶段潟湖沿岸森林植被为以栎、松为主的落叶阔叶-针叶混交林,部分样品含有个体小的常绿栎属花粉;潟湖边缘是以海滨盐生的蒿属、禾本科、藜科等草本为主的沼泽湿地景观,反映气候温暖略湿.第2阶段和前一阶段相比,草本植物花粉中喜盐碱的蒿、藜的数量增加,样品中出现较多的海生刺球藻和甲藻,并有贝类等生长,反映该段时间有较长时间的海水侵入.第3阶段针叶的松属占优势,表明气温与前阶段相比略低,高盐度有孔虫的出现可能显示潟湖出现阶段性封闭现象.     

天目山千亩田泥炭腐殖化度记录的中全新世气候变化

以14C测年为基础,构建了天目山千亩田地区泥炭沼泽剖面年龄-深度模式曲线,通过该区的腐殖化度与烧失量分析研究,发现两者呈现出很好的相关性,共同记录了该地区4 200 aBP以来的气候变化,可划分出3个主要阶段:早期(4 135±40~3 200 aBP)泥炭腐殖化度偏低,指示气候湿热;中期(3 200~630 aBP)泥炭腐殖化度偏高,指示气候温凉偏干;晚期(630 aBP以来),泥炭腐殖化度偏低,气候温凉湿润。     

8000aBP以来珠江口西南部孢粉组合特征及其古气候意义

通过分析珠江口西南部ZJK04孔柱状样孢粉组合的特征,重建了珠江三角洲地区8 000年以来植被和气候演化的历史。该孔的孢粉记录从下到上分为4个阶段:第Ⅰ阶段(8 090～7 800aBP)温暖湿润,第Ⅱ阶段(7 800～4 200aBP)温和湿润,第III阶段(4 200～833aBP)凉爽干燥和第Ⅳ阶段(833aBP以来)偏冷湿润。珠江三角洲地区气候和植被变化最显著的时期发生在4.2kaBP前后,这一时期的气候以快速变冷、变干为特征,与北半球中低纬度地区4.2kaBP的干冷事件相吻合。而830aBP之后芒萁属蕨类植物孢子含量急剧增加,可能与此时人类的活动有关。     

云南宁蒗地区中全新世晚期气候变化的石笋记录

通过对云南宁蒗县永宁区仙人洞石笋进行α-U系测年和碳氧同位素分析,建立了4 500~2 000 aBP的古气候变化时间序列。研究结果表明,永宁地区在4 500~2 000 aBP间石笋记录的冷暖事件所反映出的气候变化,大致可分为6个气候阶段:4 500~4 000 aBP气候温暖干旱;4 000~3 400 aBP气候寒冷干旱,是中全新世晚期的一次重要的气候演变转折时期;3 400~3 100 aBP气候温暖湿润;3 100~2 650 aBP气候寒冷干旱;2 650~2 400aBP气候温暖湿润;2 400~2 000 aBP气候冷凉湿润。中全新世晚期以来,石笋记录的这些短时间尺度的气候事件,明显受中—低纬度太阳辐射强度以及北半球大气环流的影响,太阳辐射强度的变化是控制印度季风演变的主要动因。石笋记录揭示印度季风的快速推进或退出(萎缩)以及百年尺度上的气候波动是太阳辐射量变化造成的结果。     

柴达木盆地尕海湖沉积物粒度特征及其古气候意义

以尕海湖DG02钻孔沉积物为研究对象,利用高分辨率的粒度数据,结合岩性、孢粉特征,分析其粒度特征及近11000aBP来的气候环境变化。研究发现,尕海湖沉积物记录了该区域湖泊水体逐渐上升又逐渐减少的过程,气候环境变化大致分为4个阶段:(1)冰消期晚期(11324～10290aBP)气候干旱,湖泊水位下降,面积收缩,水动力较强,沉积颗粒较粗;(2)早全新世(10290～8850aBP),气候转向湿润,湖泊水位上升,为浅水至深水的过渡阶段,颗粒由粗变细;(3)中全新世(8850～4400aBP),气候更加湿润,湖水水位达到最高,面积扩大,水动力达到最弱,沉积颗粒最细;(4)晚全新世(4400～200aBP),气候变干,湖泊强烈收缩,湖面下降,水动力达到最强,沉积颗粒最粗。尕海湖DG02钻孔沉积物粒度所记录的区域气候干湿变化及一些重要的干湿事件与国内外研究显示出较好的一致性。     

辽西北地区全新世中期以来环境变迁

通过对辽西北牧场泥炭层孢粉含量分析,结合^14C及辽西北地区其他地质记录,初步重建了辽西北地区全新世中期以来,即5000aBP以来的环境演变序列：5000～4400aBP为冷干,但气候仍较今日适宜,辽西地区这时为森林草原景观;4400～2750aBP以温暖湿润为主,后期气候稍冷;2750～1090aBP以冷干为主,后期稍温润;1090～250aBP以干旱为主;250aBP至现在辽西地区环境进一步向干旱化方向发展。辽西北地区环境变化的不同阶段可与当地人类发展对应,温暖湿润的环境使农业得以发展;反之,寒冷干燥、环境恶化,以牧业为主,人民生活受到限制。     

南日群岛东部海域岩芯沉积物有机碳含量和δ~(13)C_(TOC)值的变化特征及古气候环境意义

2008年在南日群岛东部海域用钻机采集长度为1 004 cm的岩芯样品,测试沉积物中总有机碳(TOC)含量、稳定碳同位素比值(δ13CTOC)、碳氮比值(C/N)、碳酸盐含量以及14C数据,分析其垂直剖面上的变化特征,阐明其沉积环境和古气候的指示意义.沉积物TOC含量变化范围为0.44%~0.74%,垂直剖面上总体显示出末次冰期和全新世中期TOC含量较高,全新世早期相对稳定,而全新世中后期TOC波动范围明显增大.C/N值在5.3~14.9之间变化,平均值为8.1;δ13CTOC值范围为-23.07‰~-21.04‰,表明沉积物中的有机质以海洋自生为主,同时混有部分陆源有机质.碳酸盐含量在3.3%~10.9%之间.TOC含量、C/N比值、δ13CTOC值在岩芯垂直剖面上具有很好的相关性.14C测年数据以及各要素测值在垂直剖面上的变化特征表明:自11 250 aBP以来该海域附近古气候有可能经历了以下4个演化阶段:①11 500~9 000 aBP期间气候寒冷、海平面下降,采样点可能为浅水区或潮间带;②9 000~8 000 aBP期间为升温期,气候由寒冷转向温暖;③8 000~4 300 aBP期间,为相对稳定的暖湿期,在后期气候出现小幅的波动;④4 300 aBP至今,气候进入明显的周期性波动期,暖湿和干冷气候多次交替变化;4 300~3 000 aBP期间为相对寒冷的时期;3 000~1 800 aBP期间为较稳定温暖期,1 800~1 000 aBP期间气温快速降低,标志着研究区进入一个新的寒冷阶段,但是自1 000 aBP以来,气候又再次出现转暖的趋势.     

新疆东部全新世气候变化特征——以巴里坤湖为例

巴里坤湖泊沉积地层较好地记录了北疆东部地区全新世以来的气候变化。通过对沉积物粒度组分及碳酸盐含量的测量分析,结合测年结果,得出北疆东部地区全新世以来气候环境变化大致经历了5个阶段：（1）8700cal．aBP以前,为全新世早期,环境变干;（2）8700～8200cal．aBP,为一过渡期,湖泊面积扩大;（3）8200～7700cal．aBP,气候以变湿为主要特点,波动较大;（4）7700～2400cal．aBP,气候较为湿润,期间存在一次明显的突发强干旱事件;（5）2400cal．aBP以来,气候转干,剖面顶部指标指示环境恶化。区域气候变化以干湿为主要特点,5500～6000cal．aBP期间的突发气候事件在大区域上与其他记录对应较好。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

INFORMATION FOR AUTHORS

<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology,     

Evaluation of the Risk of Marine Slope Instability: A Pseudo-3D Approach for Application to Large Areas

This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried out by IFREMER on 19 cores extracted at different depths (from 27 m to 1300 m) (Cochonat, Bourillet, and Savoye, 1993; Mulder et al., 1994). Many scenarios were proposed in order to explain the cause of the Nice slope failure (Habib, 1994). In this article, two of those scenarios were tested. Simulation results are presented and discussed.