南海中部海域鸢乌贼耳石形态特征分析

根据2012年9月～10月于南海中部海域采集的鸢乌贼（Sthenoteuthis oualaniensis）样本90尾,对其耳石形态特征及计量学参数进行了初步研究。结果表明,耳石样本具有明显的背区、侧区、吻区和翼区结构,背区小,侧区和翼区宽大,吻区长窄。南海中部海域鸢乌贼按照耳石形态的差异可分为3个不同的群体。耳石总长（total statolith length,TSL）、翼区长（wing width,WL）、最大宽（maximum width,MW）与胴长之间呈对数函数关系（P〈0.05）,吻区长（rostrum length,RSL）、背侧区长（dorsolateral length,DLL）与胴长之间呈线性函数关系（P〈0.05）。随着胴长的增加,耳石绝对尺寸逐渐增大,相对尺寸逐渐减小,耳石的形态结构比例基本不变,即背侧区长、侧区长、吻区长、翼区长同耳石总长之比基本保持一致,分别为48.05%、60.05%、35.44%和67.59%,其中侧区长、翼区长与耳石总长的比值随胴长增大而增加的趋势较为明显。

南海中部海域秋冬季中层渔业生物群落结构的初步研究

根据2014年对南海中部海域秋冬季2个航次中层拖网调查数据,分析了中层渔业生物种类组成、优势种和多样性等群落结构特征。共鉴定中层渔业生物241种,其中鱼类196种、头足类21种、甲壳类24种,冬季的渔获种类高于秋季,但单位捕捞努力量渔获量(CPUE)略低于秋季。相对重要性指数(index of relative importance,IRI)结果表明,秋季IRI≥100的优势种群有25种,其中IRI≥500的优势种有5种,包括蝰鱼(Chauliodus sloani)、尾明角灯鱼(Ceratoscopelus warmingii)、条带眶灯鱼(Diaphus brachycephalus)、日本乌鲂(Brama japonica)和条带多光鱼(Diplophos taenia);冬季IRI≥100的优势种群有26种,其中IRI≥500的优势种有3种,分别为典型刺虾(Oplphorus typus)、蝰鱼和太平洋帆乌贼(Histioteuthis pacifica)。秋冬季的IRI组成不存在显著性差异(P>0.05)。以个体数计算的中层渔业生物丰富度指数、均匀度指数和多样性指数冬季高于秋季,但优势度指数是冬季低于秋季。以生物量计算的多样性指标中,冬季中层渔业生物丰富度指数和多样性指数高于秋季,而优势度指数和均匀度指数则低于秋季。利用数量生物量比较曲线(abundance-biomass comparison curves,ABC)方法分析南海中部海域中层渔业生物群落的状况,结果显示,秋季中层渔业生物群落处于较大干扰状况,冬季群落处于中等干扰状况。

南海中部海域障碍层特征及其形成机制

南海中部海域（10°～19°N，108°～122°E）存在显著的季节变化的障碍层．障碍层发生概率夏季最大（52．8%），秋季次之（41．0%），春季最小（10．5％）．夏季（2000年8～9月）障碍层最显著，平均厚度约为14．2m；除114°E以东、吕宋岛以西海域为障碍层的多发区外，中南半岛东南海域（12°～14°N，110°～114°E）也存在显著的障碍层；春季（1998年4～6月）和秋季（1998年12月）障碍层平均厚度分别为6．8和11．2m，障碍层多位于114。E以东、吕宋岛以西海域．此外，吕宋岛以西海域（12。～16。N，116。～120。E）及中沙和西沙群岛附近（16。～18°N，110°～116°E）海域障碍层年发生几率超过20%，相对而言，其他海域障碍层年发生几率偏小．降水机制和层结机制分别是南海中部海域春、夏季和秋季障碍层形成的主要原因．其中，降水机制及东南向的Ekman平流较好的解释了春、夏季吕宋岛以西附近海域成为障碍层多发区的原因；此外，强降水是夏季中南半岛东南海域（12°～14°N，110°～114°E）障碍层产生的关键，反气旋涡（暖涡）有助于形成更强的障碍层，上升流对障碍层的影响有待进一步研究．

南海中部海域地震速度分析

从南海中部海域多次地球物理调查获得的速度资料中,挑选3 000多个速度谱点,经过解释直接或间接地获得该区200多条剖面上各点的叠加速度、均方根速度、层速度等多种速度资料,并计算出该区的时深转换和砂岩百分含量。综合各剖面上的速度变化和Ps值(砂岩百分含量)特征,编制了晚始新世以来地层速度和Ps值平面图,分析各时代层速度和Ps值的纵向和横向变化规律。得出南海中部海域物源早期来自西北方向,中期西南方向,最后远离物源的变化过程,海水进侵方向为东南方向。进而说明该区经历了初期冲积平原、中期滨海—浅海和晚期浅海—半深海的充填演化过程。为研究该区的地层沉积特征和沉积模式提供依据。

Vegetation Evolution in the Northern South China Sea Region Since 40 ka BP - An Attempt to Reconstruct Palaeovegetation Based on Biomization

Vegetation evolution in the northern South China Sea region since 40 500 a BP is reconstructed using biomization procedure based on pollen data from deep sea core 17940. The result shows that, it is feasible to reconstruct palaeovegetation using biomization procedure, when pollen, particularly Pinus pollen, transported by mind over long distance is excluded. Results from factor analysis suggest that humidity and temperature are the two main factors determining vegetation evolution on land around the northern South China Sea. From 40 500 a BP to 11 100 a BP, broad-leaved evergreen forest (WAMF), and montane conifers(MGRF) occurred on hills and low mountains; while steppe (STEP) predominated on the exposed shelf. The main feature of the vegetation evolution is the frequent alternation between MGRF (or WAMF) and STEP, implying abrupt changes in millennium scale between humid/cold and dry/temperate climate. All abrupt climate events could be broadly correlated with Henrich events and Dansggard-Oscherge events. One of the events around 12 700 a BP, sees the occurrence of MGRF, suggesting that climate turned humid and cold rapidly. This may be correlated with the Younger Dryas event; Broad-leaved evergreen (WAMF) predominates since 11 000 a BP. During the early Holocene and late Holocene tropical rainforest (TRFO) or tropical seasonal forest (TSFO) occurred several times.

Distribution of Organic Matter,Iron,Mangenese in Surface Sediments in the Nansha Islands Sea Area,South China Sea

Concentrations of organic matter, iron and manganese in the deep sea surface sediments in the Nansha Islands sea area, South China Sea are measured. Horizontal and vertical distributions of iron and manganese are discussed. The vertical distribution of iron and manganese in the sediments results from reduction, diffusion, and redeposition of manganese (or iron) oxide and hydroxide in the sediment. There are the maxima of iron and manganese in solid phase in the top of the sediment, which is caused by the penetration of O2 and the upward flux of Mn2+ ( or Fe2+ ). Manganese bacteria play a very important role in the cycle of solid-phase iron and manganese in the ocean environment. Manganese bacteria oxidize Mn2+ ( or Fe2+ ) in dissolved state to Mn4+ ( or Fe3+ ) in oxidized state under the aerobic condition, whereas they reduce iron and manganese in anaerobic conditions.

Characteristics of authigenic pyrites in shallow core sediments in the Shenhu area of the northern South China Sea: Implications for a possible mud volcano environment

Distinct pyrites have been recovered from a shallow sediment core from Site 4B in the Shenhu area of the northern South China Sea. Based on the lithology, texture and structure of sediments, the stable sulfur isotope of pyrite and the total organic carbon (TOC) concentration of the sediments, a distinctive sediment interface is identified at a depth of about 1 m below the seafloor in the core sediments. The pyrites only accumulate in the lower part of the core as rods and foraminifera-infillings, and mainly within three intervals marked by high pyrite concentrations. The amount of pyrite in the sediments shows no remarkable correlation with TOC in the Site 4B core sediments. The stable sulfur isotopes of the pyrite have extremely negative values ranging from 41.69‰ to 49.16‰. They are considered to be the mutual product of sulfate bacterial reduction and sulfur bacterial disproportionation. Our research proposes that Site 4B might be located in or near a possible mud volcano sedimentary environment; a large amount of methane could migrate from deep to shallow sediments in an active mud volcano and thereby play a key role in the intensity of sulfate bacterial reduction and the amount of pyrite formed at Site 4B. Further, the variation in flux of deep methane fluid by intermittent mud volcanic eruptions might result in the deposition of authigenic pyrite intervals.

Sea surface temperature evolution in the western South China Sea since MIS 12 as evidenced by planktonic foraminiferal assemblages and Globigerinoides ruber Mg/Ca ratio

Based on the detailed planktonic foraminifera faunal count and Globigerinoides ruber Mg/Ca ratio analysis of Core MD05-2901,we reconstructed the longest Mg/Ca sea surface temperature(SST) sequence of the upwelling area off Vietnam in the western South China Sea(SCS).Ocean environment,especially the SST variation,over the last 450 ka is discussed in this study.SST variation has typical glacial/interglacial alternations from 23.03°C to 29.93°C with a glacial/interglacial difference of 4.8°C on average.SST during the interglacial periods fluctuates significantly,up to 5.6°C,which is larger than the average glacial/interglacial difference.SST variation during the glacial periods is much smaller.Spectrum analysis shows that SST change dominates on the typical Milankovitch cycles,such as 112,40.7 and 23.6 ka.Evident leading of SST variation against the δ 18 O can be observed during the Terminations 1,4,and 5,which is confirmed by their cross-spectrum analysis on these cycles.MD05-2901 is the first core in the South China Sea that has multi-SST records,such as SST Mg/Ca,k' 37 U-SST and planktonic foraminiferal fauna-based SST.SSTs from different methods can be correlated with each other in glacial/interglacial time scale,whereas SST Mg/Ca records abrupt climate change events more clearly.SST Mg/Ca at MD05-2901 since MIS 5 is 0.6°C lower than that of the southern SCS on average,but equivalent to or even 2°C lower than that of the northern SCS during some interglacial period.The SST character of MD05-2901 reflects less influence of latitude,but an important role of the regional upwelling driven by the eastern Asian summer monsoon,and suggests a stronger upwelling during the interglacial periods in the western SCS.