印度洋沉积物中火山灰应用研究进展

印度洋是我国"21世纪海上丝绸之路"的重要通道,更是亚洲季风两个子系统(印度季风和东亚季风)的主要策源地,在全球变化中扮演着重要角色。海洋沉积物中的火山灰作为一种地层研究工具,不仅记录了源区、搬运介质和搬运机制的相关信息,还能有效"等时"定年,其含量和成分对研究沉积作用和构造活动具有重要意义。文章对印度洋沉积物中的火山灰应用研究进展进行了综述,包括:1)火山灰定义及其在印度洋沉积物中"等时面"的应用;2)火山灰(火山玻璃)的测试分析方法及其在追踪物质来源、火山构造与岩浆作用、印度季风演化等方面的运用。今后我国在印度洋开展火山灰研究主要应该聚焦在两方面:1)表层沉积物中的火山灰及其应用;2)火山灰与高分辨率古环境记录。可以利用火山灰定年的"等时"性探讨气候变化的区域差异及驱动因素。

现代放射虫的高阶分类现状及其生态学意义

“放射虫(Radiolaria)”这类原生动物在现代海洋和古海洋研究中具有重要的意义,但其高阶单元分类在传统形态学、细胞微结构和分子系统学研究的不断向前推进中历经了几次大的修订:Phaeodaria(稀孔虫)直至2000年后才经细胞超微结构与分子系统学证实不属于Radiolaria(放射虫);Taxopodia(列足虫)最初被认为是Amoeba(变形虫),后因细胞超微结构而归为Heliozoa(太阳虫),终由分子学证据证实属于Radiolaria;Entactinaria(内射虫)与Spumellaria(泡沫虫)并列为目阶的观点现受到分子系统学证据的质疑;Polycystinea(多囊虫类放射虫)常被用作一正式的分类阶元,但分子系统学证实Polycystinea是一个并系类群,其包含的3个目(Spumellaria、Collodaria和Nassellaria)不是起源于同一分支。此外,本文还着重分析了不同高阶单元类群的生态分布特征及环境应用前景,旨在为国内外学者呈现一个清晰的现代放射虫高阶分类最新进展,便于快速准确地了解不同高阶单元的归类现状及其生态学最新动态,促进现代放射虫在海洋生物学和生态学研究及其在古海洋、古水团和古气候重建研究中的应用发展。

Radiolarian record to paleoecological environment change events over the past 1.2 MaBP in the southern South China Sea

This note studies the Radiolarian fossil groups since 1.2 MaBP in ODP leg 184 site 1143, the southern South China Sea (SCS). The result shows that radiolarian abundance experienced a significant variation: before 0.9 MaBP it remained at the extremely low level, but increased with low extent between 0.9-0.65 Ma, which corresponded to the Mid-Pleistocene Transition stage, and it increased rapidly after 0.65 MaBP. During the whole process, the average abundance became higher and higher in each stage, and showed regularly periodic fluctuations. The obvious increase after 0.65 MaBP is inferred to result from the enhanced up-welling in this region, which was induced by the intensified monsoon circulation after the 'Mid-Pleistocene Transition'. An outstanding result of the spectral analyses is that a long oscillation of - 0.2 Ma cycle was found in the records of radiolarian abundance and complex diversity, which corresponds well to the result of other paleoceanographic indexes. This probably indicated a

Radiolarian biogeography in surface sediments of the Northwest Pacific marginal seas

Overall abundance and species composition of radiolarian faunas were analyzed in surface sediment samples from representative areas of South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea, Philippine Sea, and the western boundary current regions of the North Pacific, in order to understand the biogeographic distribution ofradiolarians in the Northwest Pacific and explore its relationship with the main environmental factors and the North Pacific circulation. The results showed that radiolarians in the Northwest Pacific surface sediments can be divided into two large biogeographic provinces---cluster A and cluster B. Cluster A is characterized by the dominance of warm-water species and distributed primarily in tropical and subtropical seas with high radiolarian abundance and diversity; whereas cluster B is predominated by cold water species and distributed mainly in the Arctic and subarctic seas with comparably low abundance and diversity. Cluster A is further divided into five subclusters, AI to A5, which correspond to East China Sea, Philippine Sea, South China Sea, Sea of Japan, and Kuroshio Current, respectively; cluster B is divided into three subclusters, B1 to B3, which correspond to Sea of Okhotsk, Bering Sea, and subarctic gyre area, respectively. Based on the relationships between radiolarian faunas and major environment parameters in different biogeographic provinces, we suggest that the sea surface temperature （SST） and sea surface salinity （SSS） are primary factors that influence productivity, composition, and distribution pattern of the radiolarian fauna in the Northwest Pacific regions, while water depth is likely responsible for regional differences in the radiolarian fauna in each marginal sea. In addition, according to the distribution and abundance patterns of common radiolarian species in different areas, we identified five special radiolarian assemblages, which may be used as indicators for main Kuroshio Current, Kuroshio-East China Sea Branch, Kuroshio-South China Sea Branch, Tsushima Current, and Oyashio Current water masses.

Radiolarian biostratigraphy in the Southern Bering Sea since Pliocene

Detailed radiolarian biostratigraphy in the Plio-Pleistocene was analyzed by using samples from IODP Site U1340 that was drilled to a core depth of 604 m in the southern Bering Sea.A total of 227 species belonging to 102 genera were identified.Based on the distributions of the radiolarian index species at Site U1340,five radiolarian zones since the Pliocene were established in the southern Bering Sea for the first time,and 25 radiolarian bioevents were recognized.Their ages were estimated on the basis of the age-depth plot that was constructed by the synthetical datum of the effective biostratigraphic and magnetostratigraphic events.The radiolarian zones at Site U1340 were systematically compared with those in its adjacent regions since the late Early Pliocene,which further improved and interpreted the biostratigraphic datum as well as their correlations in the middle-high latitude of the North Pacific.In addition,the comparative results of radiolarian zones show that Botryostrobus aquilonaris Zone emended in this paper is equivalent to the upper part of the same zone defined by Hays,1970,and Druppatractus irregularis-Dorydruppa bensoni Zone as well as Spongodiscus sp.Zone,newly proposed in this paper,are well correlated with Cycladophora sakaii Zone and Stylatractus universus Zone in the subarctic North Pacific,respectively.

Clay mineral assemblages at IODP Site U1340 in the Bering Sea and their paleoclimatic significance

Clay mineral assemblages and crystallinities in sediments from IODP Site 1340 in the Bering Sea were analyzed in order to trace sediment sources and reconstruct the paleoclimatic history of the Bering Sea since Pliocene （the last -4.3 Ma）. The re- sults show that clay minerals at Site U1340 are dominated by illite, with a moderate amount of smectite and chlorite, and minor kaolinite. Sediment source studies suggest that the clay mineral assemblages and their sources in the studied core are controlled primarily by the climate conditions. During the warm periods, clay minerals originated mainly from the adjacent Aleutian Is- lands, and smectite/（illite＋chlorite） ratios increased. During the cold periods, clay minerals from the Alaskan region distinctly increased, and smectite/（illite＋chlorite） ratios declined. Based on smectite/（illite＋chlorite） ratios and clay mineral crystallinities the evolutionary history of the paleoclimate was revealed in the Bering Sea. In general, the Bering Sea was characterized by warm and wet climate condition from 4.3 to 3.94 Ma, and then cold and dry condition associated with the enhanced volcanism from 3.94 to 3.6 Ma. Thereafter, the climate gradually became cold and wet, and then was dominated by a cold and dry condi- tion since 2.74 Ma, probably induced by the intensification of the Northern Hemisphere Glaciation. The interval from 1.95 to 1.07 Ma was a transitional period of the climate gradually becoming cold and wet. After the middle Pleistocene transition （1.07 to 0.8 Ma）, the Bering Sea was governed mainly by cold and wet climate with several intervals of warm climate at -0.42 Ma （MIS 11）, -0.33 Ma （MIS 9） and ~0.12 Ma （MIS 5）, respectively. During the last 9.21 ka （the Holocene）, the Bering Sea was characterized primarily by relatively warm and wet climatic conditions.

Distribution of living radiolarians in spring in the South China Sea and its responses to environmental factors

Using a planktonic net(62-?m mesh) and a Rose-Bengal staining method, we studied the spatial distribution of living radiolarians in spring along two sections of the South China Sea(SCS) in spring and discussed the responses of living radiolarian distribution to tropical environmental factors. Generally, the highest abundance of living radiolarians occurred at the depth range of 25–75 m, where the chlorophyll-a maximum and the highest primary productivity were. In contrast, the maximum living abundance occurred in the top 25 m in cold eddies in the open seas and the abundance decreased with depth. We found that the inhibition effect of changing salinity(due to runoffs) on living radiolarians was much stronger than the promotion effect of mesoscale cold eddies. We observed that large variation of temperature was unfavorable for living radiolarians. The dominant species composition consisted of tropical-subtropical warm species. We identified some indicator species for tropical environments. Living Didymocyrtis tetrathalamus tetrathalamus could be an indicator for tropical surface water or mixed-layer water, and even for tropical oligotrophic water. Living Tetrapyle octacantha could be used to indicate tropical thermocline and eutrophic environment. Living Acanthodesmia vinculata could indicate tropical surface and subsurface waters. T. octacantha and A. vinculata should only be used as indicators for upwelling in the open seas, i.e., far away from river mouths. Living Siphonosphaera polysiphonia preferred to form colonies, which might be related to the effect of warm eddies. Living Cyrtopera laguncula and living Cornutella profunda occurred in the tropical upper layer, even in the surface layer, which suggests that they should not be used as indicators for intermediate and deep waters.