东海DGKS96—03岩心中微体化石的古海洋学特点、δ~(18)O曲线与AMS~(14)C测年

运用微体化石的研究结果辨识岩心不同的沉积阶段的沉积特征及古海洋学特点 ,并辅以δ18O曲线及AMS14 C测年去探讨岩心的沉积时代。该岩心是 1996年 5月中国、法国、韩国科学家一起利用法国L’ATALANTE号海洋调查船在东海陆架获取的 17个岩心中的一个 ,分别做了粒度、矿物、CaCO3、微体化石、δ18O、AMS14 C测年等分析 ,初步分析认为 :依据微体化石的冷、暖水种的丰度变化 ,可以辨识出该岩心气候的 7个冷期 (C1、C2 、C3、C4 -1、C4 -2 、C5、C6、C7) ,然后结合岩心中的矿物成份、CaCO3 含量、粒度变化、AMS14 C的测年数据把岩心划分为 4个沉积阶段 ,1.晚更新世早玉木冰期沉积。 2 .玉木亚间冰期沉积。 3 .晚更新世玉木冰期沉积。 4.全新世冰后期沉积。另外 ,利用浮游有孔虫壳体对不同的沉积阶段所做的AMS14 C测年结果分别为 96 90aBP、12 980aBP ,2 6 35 0aBP ,2 796 0aBP ,37410aBP ,412 6 0aBP .     

近万年来冲绳海槽北部浮游藻类沉积率反映的环境变化

对冲绳海槽北部B－3GC柱状样的84份样品做了浮游藻类（绝大多数是沟鞭藻孢囊）沉积率分析。冲绳海槽约6790a以前的全新世早期和3620－2390aB.P.两个阶段的沟鞭藻孢囊沉积率较高,特别是在全新世早期,孢囊沉积率明显高于其他阶段。沟鞭藻孢囊沉积率的变化反映了冲绳海槽北部全新世表层海水营养和生产力水平的变化,其趋势与黑潮影响强度的变化趋势一致。在黑潮影响甚微的全新世早期,表层海水富营养且高生产力,约6790aB.P.起黑潮影响强度明显加大,表层海水营养和生产力幅度下降,只是在3620－2390aB.P.期间因黑潮影响强度减弱而表层海水营养和生产力有小幅度上升。黑潮对于冲绳槽表层海水营养和生产力的营养,不公亩在为其本身低营养、低生产力的特性,也由于其对来自我国大陆一侧陆源输入物的阻隔作用。Operculodinium centrocarpum沉积率在剖面下段高于Spiniferites spp.,上段则呈相反的情况,Spiniferites spp沉积率较高,变化的转折点（约6790aB.P.)与黑潮对冲绳海槽影响强度出现骤然变化的时间吻合。所以,Operculodinium centrocarpum沉积率高实际上指示了偏低的表层水温,约6790aB.P.冲绳海槽北部表导水温明显上升。     

Deep Flows on the Slope Inshore of the Kuril-Kamchatka Trench Southeast off Cape Erimo, Hokkaido

Deep flows on the slope inshore of the Kuril-Kamchatka Trench southeast off Cape Erimo, Hokkaido were observed for about five years from June 1989 to March 1995, using a mooring system with two current meters. In 1991 and 1993 directionally stable southwestward flows were observed at the upper layer (1000 m). These appear to be typical of the Oyashio because the characteristics of the flows were high mean kinetic energy, low eddy energy and high stability. However, the magnitudes of other mean flows at the upper layer, except for 1991 and 1993, were less than their standard deviations. This suggests that the Oyashio was observed for only a limited period of time. On the other hand, at the lower layer (3000 m) the magnitudes of the mean flows for 10–11 months were 1–3 cm s^-1 and ellipses of their eddy kinetic energy were extremely flattened in the direction of the local isobath. The directions of the mean flows in 1990, 1991 and 1993 were southwestward along the local isobath. The relationships between the upper and the lower flows are discussed in terms of monthly change of kinetic energy, since the low-frequency fluctuations longer than 30-day are predominant from the eddy kinetic energy spectra. The results show that there are cases when the kinetic energy of the monthly mean flows at the lower layers are larger than those at the upper layers. This suggests the possibility that the lower flows are in part a southward deep western boundary current.     

Correlation between Expansion Rate of the Coronal Magnetic Field and Solar Wind Speed in a Solar Activity Cycle

Thirteen synoptic maps of expansion rate of the coronal magnetic field (CMF; RBR) calculated by the so-called ‘potential model’ are constructed for 13 Carrington rotations from the maximum phase of solar activity cycle 22 through the maximum phase of cycle 23. Similar 13 synoptic maps of solar wind speed (SWS) estimated by interplanetary scintillation observations are constructed for the same 13 Carrington rotations as the ones for the RBR. The correlation diagrams between the RBR and the SWS are plotted with the data of these 13 synoptic maps. It is found that the correlation is negative and high in this time period. It is further found that the linear correlation is improved if the data are classified into two groups by the magnitude of radial component of photospheric magnetic field, |B^pho_r|; group 1, 0.0 G ≦ |B_r^pho| < 17.8 G and group 2, 17.8 G ≦ |B_r^pho|. There exists a strong negative correlation between the RBR and the SWS for the group 1 in contrast with a weak negative correlation for the group 2. Group 1 has a double peak in the density distribution of data points in the correlation diagram; a sharp peak for high-speed solar wind and a low peak for low-speed solar wind. These two peaks are located just on the axis of maximum variance of data points in the correlation diagram. This result suggests that the solar wind consists of two major components and both the high-speed and the low-speed winds emanating from weak photospheric magnetic regions are accelerated by the same mechanism in the course of solar activity cycle. It is also pointed out that the SWS can be estimated by the RBR of group 1 with an empirical formula obtained in this paper during the entire solar activity cycle.     

Assessing land-use and carbon stock in slash-and-burn ecosystems in tropical mountain of Laos based on time-series satellite images

In the tropical mountains of Southeast Asia, slash-and-burn (S/B) agriculture is a widely practiced and important food production system. The ecosystem carbon stock in this land-use is linked not only to the carbon exchange with the atmosphere but also with food and resource security. The objective of this study was to provide quantitative information on the land-use and ecosystem carbon stock in the region as well as to infer the impacts of alternative land-use and ecosystem management scenarios on the carbon sequestration potential at a regional scale. The study area was selected in a typical slash-and-burn region in the northern part of Laos. The chrono-sequential changes of land-use such as the relative areas of community age and cropping (C) + fallow (F) patterns were derived from the analysis of time-series satellite images. The chrono-sequential analysis showed that a consistent increase of S/B area during the past three decades and a rapid increase after 1990. Approximately 37% of the whole area was with the community age of 1–5 years, whereas 10% for 6–10 years in 2004. The ecosystem carbon stock at a regional scale was estimated by synthesizing the land-use patterns and semi-empirical carbon stock model derived from in situ measurements where the community age was used as a clue to the linkage. The ecosystem carbon stock in the region was strongly affected by the land-use patterns; the temporal average of carbon stock in 1C + 10F cycles, for example, was greater by 33 MgC ha⁻¹ compared to that in 1C + 2F land-use pattern. The amount of carbon lost from the regional ecosystems during 1990–2004 periods was estimated to be 42 MgC ha⁻¹. The study approach proved to be useful especially in such regions with low data-availability and accessibility. This study revealed the dynamic change of land-use and ecosystem carbon stock in the tropical mountain of Laos as affected by land-use. Results suggest the significant potential of carbon sequestration through changing land-use and ecosystem management scenarios. These quantitative estimates would be useful to better understand and manage the land-use and ecosystem carbon stock towards higher sustainability and food security in similar ecosystems.     

Palynological evidence for late Holocene environmental change on the Gimhae fluvial plain,Southern Korean peninsula: Reconstructing the rise and fall of Golden Crown Gaya State

This paper presents the results of detailed studies of palynomorphs recovered from two cores collected near the Yeanri burial mound on the Gimhae fluvial plain. Two local pollen zones were recognized on the basis of variations in the palynofloral assemblage: a lower Pollen Zone I, dominated by a Pinus‐Quercus assemblage, and an upper Pollen Zone II, dominated by a Pinus‐Quercus‐Gramineae assemblage. The palynological and molluscan analyses indicate that the depositional environments changed from a lower intertidal flat of a shallow bay environment to an upper intertidal flat in a shallow bay (before 1280 ± 110 ¹⁴C yr B.P.), and finally to a fluvial plain similar to that of today. This environmental change may have resulted from uplift along the Yangsan Fault. Afterward, the exposed area was modified by human activities, as indicated by a sudden increase in grassland herbaceous pollen grains. The loss of this bay likely had a dramatic effect on the Golden Crown Gaya State (3rd–7th centuries A.D.), which used it as a major port for regional trade, and may explain why it eventually merged with the Shilla State. © 2003 Wiley Periodicals, Inc.