西太平洋次表层海温异常与北赤道流异常海温西传

通过对热带太平洋上层XBT温度资料分析,探讨了对厄尔尼诺(El Nino)事件发生起重要作用的西太平洋暖池区次表层海温变暖异常的变化规律,揭示了影响西太平洋暖池区次表层海温变暖异常的形成机制.分析表明:西太平洋暖池区的次表层海温异常变暖与赤道太平洋的北赤道流(10°N)的海温异常存在密切关系.在El Nino事件发生的前期,位于赤道中东太平洋的异常暖水沿北赤道流温跃层潜沉向西太平洋暖池区输送,在西太平洋暖池堆积并向赤道西太平洋扩展,当异常暖水达到一定强度,并在大气的强迫下,异常暖水沿温跃层东传至赤道中东太平洋并上浮于海面,最终导致El Nino事件的爆发.北赤道流的异常海温西传是导致西太平洋暖池区次表层海温异常的重要机制,是导致El Nino事件发生的关键.     

热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应

热带西太平洋暖池是引发强烈的大气对流、驱动Walker环流和Hadley环流系统的主要热源之一,对全球、尤其是东亚气候有重要影响。针对我国在提升气候预测水平方面的重大和迫切需求,国家重点基础研究发展计划项目"热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应"于2011年7月正式立项。项目拟解决的关键科学问题包括:①调控暖池形成和变异的海洋环流多尺度相互作用过程;②海洋动力过程在暖池热盐结构变异中的作用及其机理;③暖池变异对不同类型El Nio影响机理的异同和对东亚季风变异的调制机理。围绕上述关键科学问题,项目将以暖池变异为中心,关注影响和控制暖池结构与变异的关键海洋过程,以及暖池海气相互作用影响ENSO循环、东亚季风年际变异的过程和机理,重点组织开展以下3个方面有针对性的调查研究:①热带太平洋环流和暖池的结构和变异特征;②热带太平洋环流与暖池相互作用的关键过程和机理;③暖池变异的海洋—大气耦合过程及其气候效应。在此基础上,项目将力争阐明暖池影响东亚季风和我国气候变异的过程、机理与敏感区,改进模式的混合参数化方案,提出有效提高ENSO预报技巧的同化方案,为我国短期气候预测能力的提高提供科学支撑。     

Planktonic Foraminiferal Assemblage Variations of Ontong-Java Plateau during Late Quaternary and Their Implications for Paleotemperature in the Western Pacific Warm Pool

Ocean Drilling Program (ODP) Site 807A was recovered from the Ontong-Java plateau, western equatorial Pacific. Quantitative analysis of planktonic foraminifera, combined with oxygen and carbon isotope data, reveals the glacial-interglacial variations of sea-surface temperature and the upper water vertical structure in this region during the late Quaternary. Our results indicate that since 530 ka sea-surface temperature (SST) and the depth of thermocline (DOT) have changed significantly in the western Pacific warm pool (WPWP). The average glacial-interglacial annual SST difference was up to 4.2 ℃ , and the DOT fluctuations could exceed more than 100 m, further suggesting the instability of the WPWP. The spectral analyses of SST and DOT reveal two dominating cyclicities--the typical 100 ka cycle and the semi-precessional cycle, which is significant in the tropical spectrum, indicating that late Quaternary paleoceanographic changes in the study area were influenced not only by a high latitude forcing but also by tropic-driving factors.     

Determining the spatial and temporal patterns of climate changes in China's western interior during the last 15 ka from lacustrine oxygen isotope records

China's western interior is a climatologically complex region, where climatic conditions are primarily controlled by the westerly jet stream and the Asian monsoon system. Observations reveal that the δ¹⁸O signatures of these atmospheric elements as expressed in their meteoric waters are different, and these differences are reflected in the lacustrine systems that are ultimately fed by the meteoric waters. Empirical orthogonal function (EOF) decomposition of 17 lacustrine δ¹⁸O records from this area clearly reveals the spatial and temporal structures of climate changes during the last 15 ka. The first EOF mode, dominated by sites in the NW sector, captures the temperature effect on the variability of the δ¹⁸O dataset. We interpret the variations through time in the amplitude of this mode to be indicative of changes in summer air temperature. The second EOF mode, heavily weighted by sites in the SE sector, reveals the ‘amount effect’ on δ¹⁸O, and thus its amplitude time series indicates changes in the intensity of the Asian summer monsoon. Our EOF‐based reconstructions of regional climate are generally consistent with the δ¹⁸O records of ice cores, cave speleothems and marine carbonates. Copyright © 2008 John Wiley & Sons, Ltd.     

热带西太平洋碳酸盐溶跃深度及其变化规律

碳酸盐的溶解与保存是全球碳循环的重要组成部分,研究碳酸盐溶解作用对探索碳循环机制、理解全球气候变化机理等具有重要意义。本文通过西太平洋暖池核心区雅浦海沟南部附近海域108个表层沉积物和3个柱状沉积物样品中浮游有孔虫、底栖有孔虫和碳酸钙含量等变化特征分析了海底碳酸盐溶跃深度、补偿深度及其自中更新世以来的变化规律。表层沉积物碳酸盐含量、浮游与底栖有孔虫丰度、底栖有孔虫占有孔虫全群比例、底栖有孔虫群中胶结质壳比例等多种指标变化表明,本区现代碳酸盐溶跃面(carbonate lysocline depth, CLD)位于水深3800m附近,碳酸盐补偿深度(carbonate compensation depth, CCD)约为4800m。柱状样有孔虫溶解指数(foraminifera dissolution index, FDX)的变化表明,冰期碳酸盐溶解作用减弱,碳酸盐溶跃面和补偿深度变深;冰消期碳酸盐溶解作用增强,溶跃面和补偿深度变浅。位于现代溶跃面附近的柱状岩心碳酸盐含量呈现冰期高、间冰期低的"太平洋型"旋回特征,同时古生产力替代性指标的变化曲线与碳酸盐含量没有明显的相关性,说明中更新世...     

A bi-polar signal recorded in the western tropical Pacific: Northern and Southern Hemisphere climate records from the Pacific warm pool during the last Ice Age

Western tropical Pacific sea surface temperatures and Pacific Deep Water temperatures during Marine Isotope Stage 3 have been reconstructed from the δ¹⁸O and Mg/Ca of planktonic and benthic foraminifera from Marion Dufresne core MD98-2181. This 36 m marine core was collected at 6.3°N from a water depth of 2114 m. With sediment accumulation rates of up to 80 cm/ky, it provides a decadally resolved history of ocean variability during the Last Glacial period. Surface temperatures and salinities at this site varied in close association with millennial-scale atmospheric temperature swings at high northern latitudes as reflected in the GISP2 ice core. At times of colder atmospheric temperatures over Greenland, the western Pacific was more saline and summer season SSTs were ～2 °C colder. These millennial-scale changes within the tropics are attributed to a southward displacement of the summer season ITCZ in response to steeper meridional temperature gradients within the Pacific. The benthic δ¹⁸O record from MD98-2181 documents upper Pacific Deep Water temperature and salinity variability. Benthic δ¹⁸O variations of 0.3–0.5‰ during MIS 3 indicate deep waters within the Pacific were varying by ～1–1.5 °C, with the possibility that some of the variability was due to changing salinity and minor glacial–eustatic changes. The observed deep-water variability correlates to changes in Antarctic surface temperatures and thus reflects changes in Southern Ocean temperatures at the site of Pacific Deep Water formation. The combined planktonic and benthic records from MD98-2181 thus provide a northern and southern hemispheric climate record of anti-phased variability during MIS 3 as has been inferred previously from ice core records. Furthermore, the deep sea temperature excursions appear to have led millennial variations in atmospheric CO₂ as recorded in the EDML ice core by ～1 kyr.     

古新世-始新世暖期北半球野火演化研究

古近纪是现代气候和植被形成的关键过渡期, 而野火活动与气候、植被和碳循环等存在耦合关系。开展古新世-始新世(66~34 Ma)3个特征暖期, 即古新世-始新世极热事件(PETM, 约55.9 Ma)、早始新世气候适宜期(EECO, 53.3~49.1 Ma)、中始新世气候适宜期(MECO, 约40.5~40.1 Ma)的野火活动研究, 对于揭示气候和植被变化特征及其影响具有重要意义。本研究基于蒙古高原南部二连盆地古新世-始新世野火记录, 并结合北半球该时段其他12个地点的野火研究数据, 从长尺度地质记录视角, 重建北半球野火活动特征与演变, 并探讨其驱动机制。研究结果显示古新世-始新世不同特征暖期野火发生规模和强度存在差异, PETM极端暖期较EECO和MECO暖期野火强度更大, 但不十分显著。古新世-始新世暖期并没有持续的、大规模的野火发生, 呈现"低野火状态", 总体不支持强调燃烧活动影响全球碳循环的"野火假说"。通过野火发生与温度、降水、植被以及CO2浓度等环境因子之间的关系分析, 对"古近纪低火谜题"进行初探, 认为古新世-始新世气候的季节性并不分明, 较短的干季不利于可燃"燃料"和潜在火源的形成, 很可能是新生代早期"低野火"的主因。     

赤道太平洋潜流变化特征及其与异常海温东传

应用TOGA-TAO实测海流资料(ADCP)和SODA同化海流和海温资料,分析探讨了赤道太平洋潜流的季节和年际变化特征,以及与赤道异常暖水东传的内在联系.揭示了El Nino事件中异常暖水东传的物理机制.结果表明,赤道太平洋潜流具有明显的季节变化和年际变化特征.潜流的垂直最大深度可由海表层至300~400 m,其多年平均最大流速可达100 cm/s.潜流最大中心的纬向变化位置基本维持在160°W-130°W之间.在年际变化中,赤道潜流变化特征非常明显,尤其是在El Nino事件发生过程中,赤道潜流出现明显的加强现象.其最大流速可达140 cm/s以上.在西太平洋暖池区域次表层暖水东传之前,位于中东太平洋次表层的赤道潜流就已出现加强,其最大流速中心沿温跃层不断加强和东移,“引导”来自西太平洋暖池区域次表层的异常暖水向东传播.因此,可以认为西太平洋暖池区域异常暖水的东传与赤道潜流的强度和东传存在密切关系,也就是说在El Nino事件中,赤道潜流的变化是导致西太平洋暖池区域次表层异常暖水东传的重要机制.     

The influence of large-scale circulations on the extremely inactive tropical cyclone activity in 2010 over the western North Pacific

This study attempts to understand why the frequency of tropical cyclones (TC) over the western North Pacific (WNP) was a record low during the 2010 season, by analyzing the effect of several large-scale factors. The genesis potential index (GPI) can represent, to some extent, the spatial distribution of formation in 2010. However, the GPI does not explain the extremely low TC frequency. No robust relationship between the TC number and El Niño Southern Oscillation (ENSO) was found. A comparison of the extreme inactive TC year 2010 and extreme active year 1994 was performed, based on the box difference index that can measure the quantitative difference of large-scale environmental factors. Dynamic factors were found to be important in differentiating TC formation over the WNP basin between 2010 and 1994. The remarkable difference of monsoon flows in the WNP basin between these two years may be the cause of the difference in TC formation. The unfavorable conditions for TC genesis in 2010 may have also been due to other large scale factors such as: (1) weak activity of the Madden-Julian Oscillation during the peak season; (2) warming of the sea surface temperature in the tropical Indian Ocean during the peak season, causing the development of an anticyclone over the WNP basin and associated with the westward motion of the monsoon trough, and (3) the phase change of the Pacific Decadal Oscillation (more negative) and the two strong La Niña events that have evolved since 2006.     

西太平洋暖池扩张对华北平原气候变化的影响——华北平原4万年以来升温事件的新证据

河北省黄骅市关家堡孔（ＨＧ１）,孔深４１．３ｍ,地层连续、化石丰富、分辨率高,其所含微体化石,清楚地揭示了华北平原４万年以来两次大的突发性升温事件,据研究这两次升温事件在时序上与全球性的升温事件是同步的：第一次由冷变暖起始于４００００ａＢ．Ｐ．（沧州海进期）;第二次为１００００ａＢ．Ｐ．（天津海进期）。第一次升温事件（沧州海进期）华北平原的年平均温度比今高７℃左右;比其以前的降温事件期（沧州海进与白洋淀海进之间的海退期）至少高１３℃,如此大幅度的升温事件可能是受西太平洋赤道暖池扩张影响的结果。第一次升温事件期间存在着一个短暂的变冷事件。第二次升温事件期（天津海进期）,其年平均温度比今高２～３℃。     

Process Analysis of In-situ Strain during the Ms8.0 Wenchuan Earthquake—Data from the Stress Monitoring Station at Shandan

Abstract: There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes (Ms4.0-Ms8.5) were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth’s free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks (Ms5.5-6.0) can also cause Earth’s free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.     

西北太平洋九州-帕劳海脊北部KPR12岩芯40万年来有机碳来源、埋藏特征及其环境响应

西北太平洋海陆相互作用强烈,受黑潮和亚洲大陆风尘输入影响显著,是研究海洋沉积物中有机碳埋藏与陆源输入、海洋初级生产力和海洋环境演化关系的理想靶区。本研究基于采自九州-帕劳海脊北部的重力活塞647 cm长的KPR12岩芯,分析了总有机碳（TOC）、总氮（TN）、有机碳稳定碳同位素组成（δ¹³C_TOC）、蛋白石（Opal）以及粒度等指标,初步探讨了近40万年来轨道尺度沉积有机碳的来源、埋藏特征及其影响机制。岩芯的TOC含量平均值为0.214%,呈冰期较高、间冰期较低的旋回特征。岩芯沉积物粒度的不同端元反映了研究区风尘输入大致呈冰期较高的趋势。岩芯的δ¹³C_TOC（-25.24‰~-21.04‰,平均值为-22.59‰）显示有机质以海源为主（约62%）,海源有机碳含量趋势与TOC的变化一致。研究区不同时期陆源物质的输入受风尘输送和黑潮的综合控制,黑潮增强可能对该区间冰期陆源有机碳贡献的升高有一定影响。岩芯中TOC与Opal含量的相关性分析表明,海洋初级生产力可能不是控制该岩芯有机碳含量变化的主要原因。冰期-间冰期旋回中的深层水通风条件、黑潮和北太平洋中层水的发育以及陆源细颗粒物质输入可能共同影响着本区沉积有机碳的降解与埋藏保存。

     

Architecture and evolution of the Kushiro submarine canyon in the Kurile Trench forearc slope,North‐western Pacific

An air‐gun survey, conducted over a total distance of 4356 km in the western end of the Kurile Arc offshore, has revealed the architecture and evolution of the Kushiro submarine canyon and Tokachi submarine channels of the Tokachi‐oki forearc basin. The Kushiro submarine canyon, which runs along the eastern margin of the forearc basin, is characterized by an entrenchment of up to several hundred metres in depth. The Tokachi submarine channels, by contrast, occupy the centre of the basin and consist of small, branching and levéed channels. The Kushiro submarine canyon is not connected to the Tokachi River, which has the largest drainage area in eastern Hokkaido, with a catchment area of approximately 9010 km² that includes high mountains and a volcanic region. Instead, the Kushiro submarine canyon exhibits an offset connection/quasi‐connection (probably having been connected during a prior sea‐level lowstand) with the Kushiro River (drainage area of 2500 km²) which contains the Kushiro Swamp at its mouth. To understand this unusual arrangement of rivers and submarine channels, acoustic facies analysis was undertaken to establish the seismic stratigraphy of the area. Subsurface strata can be divided into six seismic units of Miocene to Recent age. Analyses of seismic facies and isopach maps indicate that: (i) the palaeo‐Kushiro submarine canyon, which was ancestral to the Kushiro submarine canyon, was an aggradational levéed channel; and (ii) the palaeo‐Tokachi submarine channel was much larger than the present‐day channel and changed its course several times. Both the palaeo‐Kushiro submarine canyon and palaeo‐Tokachi submarine channel were fed predominantly by the ancestral Tokachi River, whereas the present‐day channels are no longer connected or quasi‐connected to the Tokachi River. Entrenchment of the Kushiro submarine canyon began in its distal reaches during the Early Pleistocene and propagated landward over time, which was possibly caused by base‐level fall (i.e. subsidence of the trench floor) or uplift of the forearc basin. Entrenchment of the upper part of the Kushiro submarine canyon began during the Middle Pleistocene, which may have been related to: (i) depositional progradation; (ii) uplift of the coastal area; or (iii) a change in source area from the ancestral Tokachi River to the Kushiro River.     

The variations of stable carbon isotope ratio of land plant-derived n-alkanes in deep-sea sediments from the Bering Sea and the North Pacific Ocean during the last 250,000 years

Two piston cores, one located far from the continents (The North Pacific Ocean: ES core), and another located comparatively closer to the continents (The Bering Sea: BOW-8a core) were investigated to reconstruct environmental changes on source land areas. The results show significant contribution of terrestrial organic matter to sediments in both cores. The δ¹³C values of n-C₂₇, n-C₂₉, and n-C₃₁ alkanes in sediments from the North Pacific ES core show significant glacial to interglacial variation whereas those from the Bering Sea core do not. Variations of δ¹³C values of land plant n-alkanes are related to the environmental or vegetational changes in the source land areas. Environmental changes, especially, aridity, rainfall, and pCO₂ during glacial/interglacial transitional periods can affect vegetation, and therefore C₃ / C₄ plant ratios, resulting in δ¹³C changes in the preserved land plant biomarkers. Maximum values of δ¹³C as well as maximum average chain length values of long chain n-alkanes in the ES core occur mostly at the interglacial to glacial transition zones reflecting a time lag related to incorporation of living organic matter into soil and transportation into ocean basins via wind and/or ability of C₄ plants to adapt for a longer period before being replaced by C₃ plants when subjected to gradual climatic changes. Irregular variations with no clear glacial to interglacial trends in the BOW-8a core may result from complex mixture of aerosols from westerly winds and riverine organic matter from the Bering Sea catchments. In addition, terrestrial organic matter entering the Bering Sea could originate from multiple pathways including eolian, riverine, and ice rafted debris, and possibly be disturbed by turbidity and other local currents which can induce re-suspension and re-sedimentation causing an obliterated time relation in the Bering Sea biomarker records.