海洋地质与环境重点实验室知识库

西太平洋暖池（WPWP）是全球海气相互作用最活跃的地区，其在全球气候演变中具有十分重要的作用，了解该区的环境演变过程对全球气候变化具有重要意义。本研究选取位于西太平洋暖池核心区的IODP 363航次U1486岩芯（02º22.34ʹS, 144º36.08ʹE，水深1332 m）上部31 m的沉积物为材料，利用浮游有孔虫氧碳同位素和Mg/Ca比值，重建了WPWP表层水体水文环境演变过程，结合相关古气候和古海洋记录，分析了冰期旋回中类ENSO状态的变化。

过去450 ka以来，U1486岩芯中浮游有孔虫Trilobatus sacculifer的δ¹⁸O的演变显示了明显的冰期-间冰期旋回特征，频谱分析呈现出了典型的偏心率周期（100 ka）、斜率周期（40 ka）和岁差周期（23 ka），说明其变化可能受到高纬和热带因素的双重驱动。T. sacculifer Mg/Ca温度重建结果显示，近5次冰期旋回中WPWP表层海水温度（SST）在25.3~30.8ºC范围内波动，末次冰盛期（LGM）SST最低值为26.1ºC，比晚全新世低近2ºC。SST整体变化与δ¹⁸O变化呈现出良好的相关性，未发现SST领先δ¹⁸O变化现象的出现。SST的演化也呈现出明显的冰期-间冰期旋回，与南极冰芯记录的大气CO₂浓度变化同步，其在轨道尺度上的变化可能是由温室气体驱动。

U1486岩芯中450 ka以来T. sacculifer壳体的δ¹³C在0.71-2.05‰之间，其值总体上间冰期略高于冰期，没有明显的冰期-间冰期旋回特征，其变化可能受到多种因素的影响。在冰期-间冰期转换期Ⅰ、Ⅱ、Ⅳ和Ⅴ期和MIS 8时均出现明显的低值事件，推测该低值事件的信号来自南大洋水团且与海气CO₂交换有一定关联。

过去450 ka里，去除全球冰体积信号后重建的海水剩余氧同位素（δ¹⁸O_sw-iv）的变化与当地日射量呈现明显的正相关关系。间冰期δ¹⁸O_sw-iv与附近站位的降水径流记录具有良好的对应关系，指示了研究区降水的变化；但与中国洞穴石笋和黄土的东亚季风降水记录呈反相位关系，表明间冰期澳大利亚季风和东亚季风有密切联系，可能指示了ITCZ的南北移动过程。

WPWP的SST记录与东太平洋冷舌区的古温度记录对比分析发现，过去450 ka来冰期时东西太平洋的温度梯度增大（>3ºC），WPWP温跃层深度加深，且间冰期的主要冰阶热带太平洋也呈现了较大的纬向温度梯度，最大可达到4~5ºC。纬向温度梯度的这一变化指示近几十万年来偏冷的冰期和间冰期冰阶热带太平洋呈现出类La Niña状态，而气候变暖期间则更趋向于类El Niño的状态。这可能是由于气候变暖过程中，地表温度升高，对流层下层水汽含量快速增加，导致边界层与对流层中层之间的质量交换减少，减弱了热带太平洋Walker环流和赤道东风带的强度，使得热带太平洋表现出更类似于El Niño的状态。

Western Pacific Warm Pool (WPWP) is the region with the most active air-sea exchange in the world, which plays a very important role in global climate evolution. Understanding the paleoenvironmental evolution of WPWP is of great significance to global climate change. In this study, the upper 31 m core composite depth below seafloor (CCSF) of IODP 363 Site U1486 (02º22.34ʹS, 144º36.08ʹE, water depth 1332 m), was used to analyze δ¹⁸O and Mg/Ca of planktonic foraminifera Trilobatus sacculife. Comparing with previous paleoclimate and paleocean studies, we reconstructed the hydrological evolution of the surface water in WPWP and thus to investigate the potential linkage of ENSO-like states between the warm/cold periods in the glacial/interglacial cycles.

The δ¹⁸O record of core U1486 has shown obvious characteristics of glacial-interglacial cycles over the past 450 ka. The spectrum analysis shows typical periods of eccentricity (100 ka), obliquity (40 ka), and precession (23 ka), which means that and the changes of δ¹⁸O in WPWP may be driven both by high latitudes and tropical regions. The Mg/Ca-temperature results of T. sacculifer indicate that the Sea surface temperature (SST) in the WPWP during the last five glacial-interglacial cycles ranged between 25.3ºC and 30.8ºC. The minimum SST at the site during the Last Glacial Maximum (LGM) is 26.1ºC, nearly 2ºC lower than that during the late Holocene. The SST changes do not lead the changes of δ¹⁸O and exhibit a close similarity with atmospheric CO₂ content for the whole study period, which also show characters of glacial-interglacial cycles. We speculate that greenhouse gas forcing is the primary driver SST changes in orbital sacles in WPWP region.

The δ¹³C record of core U1486 T. sacculifer over the past 450 ka ranged between 0.71‰ and 30.8‰, and the variation of δ¹³C does not show obvious trends of glacial-interglacial cycles. Generally, the values in interglacial periods are slightly higher than it in glacial periods, and the change of δ¹³C may be controlled by various factors. There are obvious δ¹³C mimimum events during termination Ⅰ, Ⅱ, Ⅳ, Ⅴ and MIS 8. We guess that the low δ¹³C signals may be from Southern Ocean and be related to CO₂ air-sea exchange.

δ¹⁸O_sw-iv of core U1486 was calculated by removing ice volume effect from δ¹⁸O_sw,which showed a positive relationship with local insolation since 450 ka. During interglacial periods, it corresponds well to the river runoff records of nearby core stations, which means it can be used to reflect the change of precipitation in the study area. δ¹⁸O_sw-iv shows an anti-relationship with east Asian monsoon precipetion records, which indicate a tight relationship between the Australian monsoon and the east Asian monsoon during interglacials. And the changes may indicate the meridional shifts of Intertropical Convergence Zone (ITCZ) in obitial time scales.

By comparing the SST records derived from the cores located in the WPWP and the Eastern Pacific Cold Tongue (EPCT), it is found that the zonal temperature gradient of the tropical Pacific Ocean was more than 3 ºC, along with deeper thermocline in the WPWP, during the glacial periods. In addition, larger zonal temperature gradients, with a maximum of 4~5ºC, were recorded in the major stadials of interglacial periods. The patterns of the zonal temperature gradient across the tropical Pacific Ocean imply that the ocean conditions therein showed more La Niña-like states in the colder periods and more El Niño-like states during the warming stages over the past few hundred thousand years. When the earth-surface temperature rises, the rapid increase of water vapor concentration in the lower troposphere could weaken the mass exchange between the boundary layer and the troposphere, and thus weaken the intensity of the Walker circulation and the eastliers in the tropical Pacific that may result in a decreased zonal temperature gradient with a more El Niño-like state.

目 录

第一章 绪论

1.1 引言

1.2 西太平洋暖池与现代ENSO过程

1.3 浮游有孔虫在古海洋学研究中的应用

1.4 δ¹³C的古海洋学应用

1.5 西太平洋暖池区的古海洋学研究进展

1.5.1 表层海水古温度重建

1.5.2 热带太平洋的类ENSO式变化

1.6 主要研究目标和内容

第二章 区域地质与环境

2.1 俾斯麦海地质特征

2.2 区域气候特征

2.3 区域水文特征

第三章 研究材料和方法

3.1 研究材料

3.2 研究方法

3.2.1 微体古生物样品处理

3.2.2 有孔虫稳定氧碳同位素分析

3.2.3 浮游有孔虫Mg/Ca比值分析

3.3 年龄框架

第四章 研究结果

4.1 有孔虫壳体氧同位素

4.2 有孔虫壳体碳同位素

4.3 浮游有孔虫Mg/Ca-SST

第五章 西太平洋暖池核心区表层水体结构演化

5.1 表层海水温度演化

5.2 表层海水盐度演化

5.3 冰消期δ¹³C低值事件

第六章 热带太平洋的类ENSO变化

6.1 冰期时的类ENSO状态

6.2 西太平洋暖池其他岩芯和TR163-19岩芯SST对比

第七章 结论

参考文献

致 谢

作者简历及攻读学位期间发表的学术论文与研究成果