2015, Vol.35
1 引言
在全球升温的背景下，为了在大范围的边界条件下更细致和准确的描绘、模拟海气过程和预测未来，我们需要去了解长期的环境历史记录。许多研究表明，热带太平洋现代厄尔尼诺-南方涛动（ENSO）过程对全球气候具有重要作用[1, 2, 3, 4, 5]，且在过去也存在类似于现代ENSO的变化[6, 7, 8, 9, 10]。要了解ENSO的变化趋势，需要积累多种指标来指示时间跨度长且连续的类ENSO过程[11]。暖池核心区是指西太平洋暖池内位于巴布亚新几内亚北部，年均温超过29℃的海区。该海区海气相互作用强烈，是驱动全球大气环流的最大水汽源和热源，其海区水文变化影响着ENSO和热带辐合带（ITCZ）的变动，与东亚季风也存在一定关系[1, 12, 13, 14]。年际上，暖池降水与ITCZ季节性移动和北部冬季风向赤道寒流紧密相关[15, 16]，其时空变化强烈影响着ITCZ的位移和东亚（夏）季风[17, 18, 19, 20]，海洋表层温度（SST）的微弱变化都可能导致全球气候模式的动态变化[21]，因而了解暖池SST变化的控制过程是了解全球气候变化的关键[22]。但是暖池区水文变动、ENSO过程和ITCZ变动在过去冰期-间冰期旋回中都很复杂，各自本身的变化特征和相互关系一直都存在着很多争议。因为热带太平洋海区沉积速率低、样品难以获取等原因造成之前对其研究比较匮乏，资料也较少[11]，所以有必要加强研究，增强对其在全球变化中作用的认识。
在末次盛冰期（Last Glacial Maximum,简称LGM）暖池区降温问题上，早期生物转换函数等方法得到SST相对于全新世低 1±2℃[23, 24]，但改进的生物转换函数研究支持比CLIMAP低2℃或者更低，如Uk37数据表明降温2～3℃[25]。有孔虫壳体Mg/Ca法得到平均区域下降约3℃[7, 26]，经盐度矫正的Mg/Ca法得到约为4℃的变化[27]，与二元同位素指标结果一致[28]，一些模型研究也支持上述温度较大降幅的观点[29, 30]。Koutavas等[31]利用Mg/Ca得到暖池区在LGM呈现El Niño状态，但Dubois等[32]利用U37k得到的温度空间分布表明东太平洋冷舌降温更剧烈，表明信风加强并且上升流加强，代表着LGM时期类似La Niña状态。Martínez等[33]通过有孔虫种群研究得到LGM热带东太平洋的SST经向梯度变大表明其La Niña状态以及东、西温跃层梯度加强[34]。de Garidel-Thoron等[26]运用多指标重建暖池古海洋环境并没有显示出在末次冰消期类ENSO气候变化的证据。ITCZ的平均位置主要受经向SST梯度的控制，并且影响着暖池的水文变动和东亚季风活动，但ITCZ和ENSO之间的关系一直没有得到清楚的认识[13]。由于种种矛盾的存在，热带太平洋在驱动冰期-间冰期气候变化中的角色问题一直没有解决。本文拟利用暖池核心区沉积物浮游有孔虫壳体的地球化学指标与其他指标对比来探讨过去20万年来暖池区的水文变动及其与ENSO、ITCZ和东亚季风之间的关系。
2 材料与方法研究采用岩芯为KX97322-4孔(00°01′S，159°14′E)，该站位于赤道西太平洋Ontong-Java海台(图1)，由2008年暖池区专题航次利用重力取样器获得。站位水深2362m，处于海区溶跃面(CCD)(约3400m)以上，样品主要成分为有孔虫软泥[35]，对柱状样上部3.2m按2cm间距取样进行有孔虫壳体Mg/Ca分析，共取160个样品。样品的年代地层框架是利用张帅等[36]基于本孔Globigerinoides ruber壳体的 δ 18 O(记作 δ 18 Oc)与RL04标准曲线对比及G. ruber(pink)的末现面(120ka B.P. )建立，底部达到MIS 6期，年龄约为188ka。
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图1 KX97322-4站位和对比站位的位置，以及热带辐合带(ITCZ)的夏季位置(蓝线)[35] Fig.1 The location of core KX97322-4 and other cores mentioned，the blue line represents the position of ITCZ in summer[35] |
KX97322-4孔样品中G. ruber壳体Mg/Ca分析，先在实体显微镜下挑选完整无损、洁净的G.ruber壳体20枚，壳径为250～300μm。利用Barker等[37]的Mg清洗方法，通过压碎后加乙醇超声去粘土、加1 ％ 的H2O2碱性缓冲溶液去有机质、镜下去杂质、HNO3(0.001M)稀酸淋洗等步骤处理样品[38]。后利用中国科学院海洋研究所海洋地质与环境重点实验室电感耦合等离子发射光谱仪(ICP-OES，Thermo iCAP 6300 Radial)进行测试获得结果，分析精度约0.44 ％ (1σ，RSD)，相对误差约0.42 ％。
由于有孔虫在成壳过程中受周围环境水体化学状态的影响，其壳体的 δ 18 Oc会记录当时周围海水温度(SST)和盐度(主要反映于海水 δ 18 O，记作 δ 18 Osw)的变化，而 δ 18 Osw变化又主要受当地水文和全球冰量变化即海平面变化控制[39]。前人研究表明[40]有孔虫壳体的Mg/Ca与海水温度之间存在着较稳定的函数关系Mg/Ca(mmol/mol)=B×exp[A×T(℃)]，其中A和B是两个指数常量，A代表Mg/Ca对温度的敏感程度，即随温度增加的速率，B代表属种特异性。因而可利用壳体的 δ 18 Oc去除温度和全球冰体积变化来估算当地水文变化(当蒸发大于降雨时海水H216 O 减少同时海表盐度上升)[41, 42]。参照张帅等[36, 38]G. ruber壳体的 δ 18 Oc和Mg/Ca结果，通过Thunell等[3]改进的Bemis等[43]利用浮游有孔虫Orbulina universa在低光度实验环境下的推算公式(1)来计算当地海区的 δ 18 Osw。本文利用Waelbroeck等[44]代表过去海平面变化的全球平均 δ 18 Osw记录，来去除全球冰体积变化对KX97322-4记录的影响，并记为 δ 18 Osw-iv。
利用Anand等[40]沉积物捕获器建立的Mg/Ca公式(2)估算G. ruber壳体Mg/Ca指示的表层海水温度(SST)，其总结了前人的研究并考虑影响Mg/Ca比值变化的其他因素，如实验室误差等等。
表层海水盐度(SSS)估算利用LeGrande和Schmidt[45]的经验公式:
Mg/Ca古温度计相对于其他指标有其独特的优势，从深海岩芯得到的同源有孔虫壳体的Mg/Ca和 δ 18 Oc使分离SST和 δ 18 Osw变化的幅度和时间成为可能，且适用于赤道西太平洋这样高温贫营养的海区[40, 46, 47, 48]。暖池核心区的季节性温盐差异很小，表层浮游有孔虫G. ruber壳体几乎不受季节变化影响，主要反映其生存环境的年均变化。对KX97322-4孔G. ruber壳体Mg/Ca通过公式(2）得到该海区MIS6以来的SST变化(图2b)。样品表层的SST估算结果为29.17℃，与现代该海区表层海水温度29.2℃[7]基本一致。暖池核心区SST变化整体呈现出良好的冰期-间冰期旋回特征，在冰期MIS2～MIS5d和MIS6期都呈现出明显变冷，相应的降温幅度分别可达3.3℃和3.6℃。冰消期都表现出快速增温现象，几乎都是从一个极小值在短时间内快速上升到极高值，然后在间冰期又逐渐下降。SST在末次冰期（MIS2～4）阶段温度波动剧烈，变化范围在26～28℃之间，在67.3ka B.P. 出现最低值25.9℃，在MIS5e达到200ka以来的最高值，为30.17℃。SST在MIS6期呈多次阶梯式升温。
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图2 MIS 6以来KX97322-4孔 δ 18 Oc(a)、SST(b)、 δ 18 Osw(d)与 δ 18 Osw-iv(e)的变化，其中虚线(c) 为Waelbroeck等[44]全球平均 δ 18 Osw Fig.2 The variation of indexes of Core KX97322-4 since MIS 6，including δ 18 Oc(a)，SST(b)，δ 18 Osw (d) and δ 18 Osw-iv (e)； the dash curve (c) represents the global mean δ 18 O[44]sw |
末次盛冰期(LGM)时，SST在20.1ka B.P. 出现最低值26.2℃，约比现今下降 2.9±0.7℃(图2b)，与邻近站位ODP806B[7]、MD97-2138[26]和WP7[49]等的Mg/Ca估算结果具有很好的一致性，而Tripati等[28]利用二元同位素指标得到的结果甚至超过4℃，巩固了暖池在LGM时期降温幅度并不小于2℃的论断。根据KX97322-4孔G. ruber的SST与 δ 18 Oc之间的关系(图2a和2b)可以看出，在整体趋势上，两者表现出很好的一致性，都呈现出间冰期高冰期低的特点； 但在冰期及间冰期时暖池核心区的SST变化却和 δ 18 Oc值的变化存在一定差异。在LGM时，δ 18 Oc值达到了最低值，但是此时的暖池核心区的SST尽管很低，并没有出现末次冰期的最低值，而是持续处于低温状态，相对于整个末次冰期而言保持稳定。在MIS 4～MIS 5e之间，δ 18 Oc有一个明显的正偏过程，但SST却没有发现这种明显地阶梯变化。在MIS 6期，暖池核心区SST变化和 δ 18 Oc值之间的变化呈明显地相反趋势，δ 18 Oc值在MIS 6期呈阶梯状正偏，而SST却呈阶梯状上升。
利用公式(1)得到的 δ 18 Osw主要反映当地SSS的变化，表层样品的 δ 18 Osw为0.46 ‰ ，利用公式(3)重建的盐度值为34.48 ‰ ，与海区现代 δ 18 Osw值0.3 ‰ [50]和SSS值34.6 ‰ 相近[7]。LGM时 δ 18 Osw值约为1.36 ‰ ，估算的SSS值为36.75 ‰ ，相对于全新世上升了约2.27 ‰。从 图2c和2d可以看出暖池区海水盐度总体上呈现出冰期高间冰期低、冰消期快速升高的特点，近似于Waelbroeck等[44]的全球平均 δ 18 Osw变化趋势，但是在各个时期却又与其存在着明显地差异。暖池区 δ 18 Osw的最高值和最低值出现在MIS 6期(大约147.1ka B.P.)和末次间冰期MIS 5e期(大约117.7ka B.P. )，分别为1.76 ‰ 和0.35 ‰ ，与MIS 6和MIS 5e全球平均 δ 18 Osw的最高值和最低值的出现一致，体现了全球冰量的变化特征:MIS 6期全球冰体积可能比LGM时期还要大、MIS 5e期全球冰体积要比现在还要小。
3.2 东、西太平洋温盐差异KX97322-4站位的结果与邻近站位ODP806B[7]对比(图3)整体上都存在着很好的对应关系，细微差异可能缘于样品分辨率差异。西太平洋暖池KX97322-4和ODP806B站位的结果[7]与东太平洋冷舌TR163-19站位的结果[7]进行对比(图3)，200ka以来暖池区与冷舌区G. ruber壳体的 δ 18 Oc在间冰期差值较小，但是在冰期差值较大。在MIS 6期，整体上暖池处于升温状态。在大约170～180ka B.P. ，赤道纬向温度梯度高，δ 18 Oc负偏。而在大约135～150ka B.P.，赤道纬向温度梯度降低，δ 18 Oc正偏。模拟实验表明MIS 6期受 El Niño 主导，高纬降温冰盖建造可能在热带太平洋变暖时加速[51, 52]，此时暖池可能作为一个重要的水汽源向两极输送水汽以促进冰席的增长。冰川的建造源于能量向海洋供给的增加导致蒸发和水汽循环加强并输送到冷的极区，一定阈值内的升温并不能带来冰川的瓦解[53]。由于受日射率变化的影响，MIS 6期高纬处于异常冷的状态[52]，因而主要受南部高纬控制[10, 54]的赤道东太平洋SST也维持在较低水平。SST数据表明西太平洋暖池区从MIS 6以来SST都高于东太平洋冷舌区，并且两者温度梯度在冰期和间冰期幅度基本相似，但在冰消期两者温度梯度最小，可能在冰消期全球升温的背景下赤道东、西太平洋同时增温，且东太平洋的增温速率和幅度要高于西太平洋造成的[6]。在现代全球变暖过程中极端 El Niño 事件发生频率会增加或翻倍[4]，其原因在于赤道东太平洋表层升温快于周围海区(赤道快于赤道外，东赤道快于西赤道)，ITCZ向赤道移动[55]，促进东赤道区域大气对流频繁发生[56, 57]。许多模型研究表明东赤道太平洋升温要比西赤道太平洋多[2, 58]，东太平洋表层升温要比西太平洋更加敏感[59]。Sun[59]对观察的热带太平洋热平衡数据分析表明 El Niño 是热带太平洋向极传热的主要机制——向极传热是间歇性的，这些阶段和 El Niño 的发生相呼应。冰消期阶段，赤道地区夏季日射率幅度明显增大(图4c中虚线)，促进赤道海区的快速升温，而这种赤道东、西太平洋温度梯度的减小，可能揭示在这种升温时期热带太平洋整体上呈现出一种类似 El Niño 的状态并且通过这种状态促使全球升温，热带太平洋在全球变化中可能起着积极的推动作用。
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图3
赤道东、西太平洋表层水体各指标对比 赤道西太平洋KX97322-4孔和ODP806B孔与赤道东太平洋TR163-19孔有孔虫壳体氧同位素 δ 18 Oc (a)、SST (c) 以及海水氧同位素 δ 18 Osw (e)对比[7]； (b)和(d)分别为东、西太平洋SST差值和 δ 18 Osw差值； ΔSST越小越趋向于类 El Niño 状态 Fig.3 The comparison of the surface water proxies between the Western and Eastern Equatorial Pacific. The comparison of δ 18 Oc (a)，SST (c) and δ 18 Osw (e) between the Western Equatorial Pacific and the Eastern Equatorial Pacific. The core KX97322-4 and ODP 806 in the Western Equatorial Pacific and core TR163-19 in the Western Equatorial Pacific[7]，(b) and (d) represent the differences between the SST and δ 18 Osw，when ΔSST becomes smaller，it likely to be in the El Niño -like status |
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图4
热带西太平洋和东亚季风降雨记录对ITCZ位移的指示 (a)中国石笋 δ 18 O记录[62]；(b)MD05-2920孔 ln(Ti/Ca)[63]；(c)MIS 6以来KX97322-4孔降雨变化；(d)KX97322-4孔热带SST记录、全球平均δ18Osw[44]和南极Dome C冰芯δD记录[64]；(a，c)虚线为日射率变化曲线 Fig.4 The indication of the ITCZ position from the precipitation records of Western Tropical Pacific and East Asia. (a)δ 18 O record of Chinese caves[62]； (b)the ln (Ti/Ca) record of core MD05-2920[63]； (c)the precipitation record of core KX97322-4； (d)tropical SST，global mean δ 18 Osw[44] and Antarctic Dome C ice core δD records[64]. (a，c)Dash lines represent the variation of insolation |
现代西太平洋暖池和东太平洋冷舌的 δ 18 Osw分别为0.3 ‰ 和-0.1 ‰ [50]，存在着0.4 ‰ 的差异。对比东、西太平洋之间的 δ 18 Osw变化(图3d)可以发现，两者盐度梯度在MIS 2～4较小、近乎相等，在间冰期(MIS 1和MIS 5)较大，差值在0.3 ‰ ～0.6 ‰ 之间。对比全球平均 δ 18 Osw可以发现在赤道东太平洋更趋近于冰期-间冰期全球平均的状态，而赤道西太平洋在冰期 δ 18 Osw与东太平洋冷舌相比偏负，即盐度相对偏低。赤道东、西太平洋SST差值也较大，这种变化可能是由于西太平洋降雨量增加所造成的，暖池区在冰期可能经历着类似 La Niña 的状态，冰期由于东、西太平洋温度梯度大信风加强导致向西输送水汽增加从而使暖池区降雨增加[7, 34]。 de Garidel-Thoron等[26]研究表明西太平洋暖池区在冰期阶段表层水更淡并且存在一个长期的盐度降低过程。而张帅等[35]通 过对KX97322-4孔的温跃层深度重建得到暖池区温跃层在过去冰期间冰期循环中一直处在不断变化之中，总趋势上在MIS 6时期加深，与有孔虫表层种相对丰度变化一致； 而在末次冰期变浅，与有孔虫表层种相对丰度变化相反。Sagawa等[9]利用暖池区多种有孔虫壳体研究表明在冰期暖池区温跃层比表层水多降温1～2℃，温跃层变浅，并且暖池区的低盐度是由于低SST抑制蒸发造成的，而上层沃克环流并不强，即不存在强的大气输送； 其他降水指标记录[60]和现代模拟实验[61]也证明此时降雨没有增强。Stott等[8]则提出在冷期暖池区可能处于 El Niño 状态，而此时大气对流从印度尼西亚向东移动使该海区降雨加强。MIS 6期尽管属于冰期，但是赤道东、西太平洋之间的盐度差异却不稳定，此时西太平洋暖池呈现出阶梯式升温过程，而每次快速升温时(约150ka B.P. 和170ka B.P.)，都对应着盐度差值的增大，类似于冰消期变化，暖池区可能因向两极输送水汽[51]而使得当地盐度增大。过去模拟研究表明在MIS 6期暖池区 El Niño 占主导地位[52]，MIS 6期 El Niño 发生频率高于MIS 5e期[51]。海区的盐度变化不仅受当地水文的变化影响，还受全球冰体积的变化影响，因而只能反映海区盐度的变化。
综上所述，在冰消期和冰期升温阶段，热带太平洋呈现出类 El Niño 状态，热带向两极释放热量、输送水汽。MIS 6期赤道西太平洋SST呈现出阶梯式升温状态，此时热带向两极输送水汽促进了当时两极冰盖的建造从而使得全球冰体积进一步扩大化。
3.3 暖池核心区降雨与ITCZ的关系δ 18 Osw去除全球冰量变化对其的影响可以得到暖池核心区当地水文变化的情况，海区上升流很弱[47]，表层水主要受降雨-蒸发的差异控制。当 δ 18 Osw-iv值正偏时，表明此时蒸发去除H216 O的作用较强，水汽向暖池外运移，当地降雨量减少，而 δ 18 Osw-iv值负偏时则表明此时水汽从热带外向暖池输运，降雨量增大[41, 42]。整体上最近两个冰期 (MIS 2～5d和MIS 6)δ 18 Osw-iv值相对较轻(图4c中实线)，暖池区冰期降雨量普遍较大，而在间冰期相反。而冰期暖池区SST也明显低于间冰期，且此时赤道东、西太平洋表层温差也较大，信风强劲，外来水汽输入多，热带太平洋海区水汽蒸发不足，从而造成冰期 δ 18 Osw-iv处于低值期。
KX97322-4站位处于ITCZ控制区[65]，位于ITCZ主轴线以南[12, 13, 66, 67]。北半球夏季ITCZ北移，该海区的降雨量会有所减少，北半球夏季风携带水汽向北输运促使降雨增加[60]。从McGee等[67]对ITCZ变动的研究可知，从 100°～170°E之间ITCZ的南北变动是同向的。在冰期(间冰期)，ITCZ收缩(扩张)，边界向赤道收缩(向两极移动)； 在冰阶(间冰阶)，ITCZ南移(北移)[65]。巴布亚新几内亚北部沿岸降雨径流指标ln(Ti/Ca)显示(图4b)，ITCZ的移动与当地降雨变化具有对应关系，当ITCZ南移时，暖池区降雨量会增加[63]。通过KX97322-4孔 δ 18 Osw-iv与巴布亚新几内亚MD05-2920孔ln(Ti/Ca)[63]对比(图4)发现两指标的峰谷值之间(MIS 1～2和MIS 5～6)具有很好的对应关系，当ITCZ南移，暖池区降雨量增加时，巴布亚新几内亚岛的地表径流相应加强，从而使得Ti输入增多。但两指标之间却也存在着幅度和变化上(MIS 3～4)的一些差异，KX97322-4孔位于暖池核心区的中部，而MD05-2920孔则位于核心区的边缘，并且受海陆相互作用较大，陆地因素较多，可能造成二者指标变幅呈现一定的不一致。
中国洞穴石笋(葫芦洞、三宝洞和董哥洞)、韩国石笋和西太平洋沉积记录表明受ITCZ移动控制北半球中纬降雨与南半球之间存在跷跷板关系[62, 68, 69]，北半球中纬水文变化与北半球季风变化一致[65, 70]。暖池核心区的 δ 18 Osw-iv及ln(Ti/Ca)与中国石笋记录[62]对比发现他们之间具有明显的相关性(图4)，当暖池核心区降雨减弱时，对应着ITCZ北移、北半球石笋季风降雨记录的增强，并伴随着夏季日射率的增大，此时全球气温和暖池SST也处于相对较高水平。说明ITCZ的变动对暖池区的水文变化有着很大的影响，且与岁差控制的日射率变化相关。对婆罗洲石笋研究也发现热带太平洋水文对两半球高纬气候过程和外部辐射驱动敏感[60]，当北半球处于冷事件时，ITCZ南移使印澳季风降雨加强[20, 71]，暖池核心区降雨的强弱与东亚季风的变化存在跷跷板的关系。
由于ITCZ对暖池水文变化有影响，因而暖池区水文变化既反映ENSO也反映ITCZ的变化。最近两个冰消期，全球升温背景下由于东太平洋的快速升温减弱纬向温度梯度[6]，暖池区呈现出类似 El Niño 的状态，此时暖池区降雨量呈现减少趋势，水汽蒸发向外输送，ITCZ处于扩张状态[65]，南界南移北界北移，使得南北半球降雨增强。在两个冰期阶段(MIS 2和MIS 6)热带西太平洋ln(Ti/Ca)值较大[63, 72]，而δ 18 Osw-iv值较低，分别达到-2.3、-2.6(图4b)和-0.05 ‰ 、0.17 ‰ (图4c)，赤道太平洋纬向SST梯度维持在3℃左右(图3b)，暖池区降雨量维持在较高水平，而此时ITCZ向赤道收缩[65]，暖池区可能呈现出类似 La Niña 的状态，沃克环流较强，降雨量较大。一些模拟实验表明ITCZ对半球间温度梯度敏感[73, 74]，冰期南北半球温差大，ITCZ多位于赤道北部[73]，因而可以维持北半球夏季风的强度。而暖池区的相对高温可能使ITCZ的南缘依然在赤道附近加强降雨，使暖池一直处于 La Niña 状态。而在冰期内，当日射率强度较高时，赤道外升温幅度要大于赤道，从而促使ITCZ进一步北移(图4)。而此时赤道太平洋纬向温度梯度减弱(在143～152ka B.P. 温差从4.7℃到2.2℃； 170～180ka B.P. 温差从2.6℃到1.4℃)(图3b)，使暖池偏向 El Niño 状态，降雨少而蒸发多，其水汽向赤道外输运从而增加中高纬季风降雨、促进两极冰盖建造使全球冰体积逐步变大(全球平均 δ 18 Osw从0.7 ‰ 到1.0 ‰ 、0.57 ‰ 到0.64 ‰ [44])(图4d)。在间冰期，赤道太平洋纬向温度梯度也较高(图3b)，类似于冰期，而此时如南极冰心δD和热带SST记录指示(图4d)，全球处在一种逐步降温的状态。在这种状态下，ITCZ处于逐渐萎缩且向南偏移的过程。当日射率处于低值时，全球降温加速，暖池 La Niña 状态又促进ITCZ南偏加强，北半球夏季风减弱，降雨减少，中国洞穴石笋 δ 18 O升高[62]； 但当日射率处于高值时，全球又开始升温，La Niña 状态被缓和，ITCZ向北移动加强北半球夏季风，中国洞穴石笋 δ 18 O降低[62]。
从冰期-间冰期尺度上看，暖池的变动明显受全球冰量变化控制，即在幅度上受地球轨道的偏心率控制。而从岁差驱动的日射率与暖池区降雨和北半球季风的关系来看，岁差驱动的日射率的变动明显超前于后两者，说明暖池区降雨和季风变动明显受岁差驱动[75]。北半球夏季日射率增加可以产生强的半球间表层温度梯度并导致南半球夏季风系统降雨减少，北半球热带水文循环加强。低纬度海区ENSO的变动也主要受岁差控制[1]。ENSO主导着热带气候的变化，与ITCZ的位置相关[18, 19, 76]。由此可见，暖池区在全球升温过程中可能处于类似 El Niño 状态，而降温过程中则可能处于类似 La Niña 的状态。ITCZ和ENSO主要受外部辐射驱动控制，而ENSO可能对ITCZ则起着内部系统调谐的作用。
5 结论(1)MIS 6以来冰期间冰期旋回中暖池核心区SST也存在着较大的波动，MIS 2～5d和MIS 6期分别达3.3℃和3.6℃。LGM时SST最低值为26.2℃，比现今下降 2.9±0.7℃。在MIS 6期，暖池核心区SST变化和 δ 18 Oc值之间的变化呈明显地相反趋势，δ 18 Oc值在MIS 6期呈阶梯状下降，而SST却呈阶梯状上升。δ 18 Osw在MIS 6出现最大值1.76 ‰ ，在MIS 5e达到最小值0.35 ‰。
(2)在冰消期和冰期升温阶段，热带太平洋呈现出类 El Niño 状态，热带向两极释放热量、输送水汽。MIS 6期赤道西太平洋SST呈现出阶梯式升温状态，此时热带向两极输送水汽促进了当时两极冰盖的建造从而使得全球冰体积进一步扩大化。
(3)过去热带太平洋类ENSO过程可能与ITCZ的移动和变化之间存在着重要的关系，进而与东亚夏季风降雨之间存在密切的联系，ENSO可能对ITCZ则起着内部系统调谐的作用。
致谢 感谢审稿专家提出的富有建设性的修改意见； 感谢杨美芳老师的认真负责和在文章修改中给予的帮助。
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Abstract
The Western Tropical Pacific plays a critical role in global water vapor and heat transport. Many studies had shown the strong correlation between tropical climate and high latitude climate variability, in particular, the Intertropical Convergence Zone (ITCZ) migration. But there is still little known about how they cooperate with each other. In this work, we studied the top 320cm gravity core at site KX97322-4(00°01'S, 159°14'E, water depth 2362m) at 2cm steps, which was recovered from the Ontong-Java Plateau in the Western Equatorial Pacific (WEP), the center of the Western Pacific Warm Pool (WPWP), where now the annual average temperature is more than 29℃. The age model is based on the correlation of the planktonic foraminiferal δ18O record with the LR04 reference benthic stack and the last occurrence (LO) (ca.120ka B.P.) of Globigerinoides ruber(pick)[35]. The bottom age could be ca.188ka B.P.(MIS 6). By combining planktonic foraminifera G. rubercalcite Mg/Ca and δ18O, we obtained the local Sea Surface Temperature(SST)and Salinity (SSS) over the past ca.200ka. In general, the WPWP SST swift culminated in deglacial then declined until the next deglacial. During the last two glacial (MIS 2~5d, MIS 6), the Western Tropical Pacific SST cooling could be 3.3℃ and 3.6℃ respectively. During MIS 2~4, the SST was 26~28℃ and got it's minimum value 25.9℃ in 67.3ka B.P. During MIS 6 SST was warming multisteply and attended its maximum value 30.17℃ in MIS 5e. In the Last Glacial Maximum (LGM), the SST minimum value in the center of WPWP was 26.2℃, about 2.9±0.7℃ cooler than now. We use the sea water δ18O(δ18Osw) value minus the global mean δ18Osw to remove the influence from ice volume change to get the local precipitation history. The maximum and the minimum value of the δ18Osw is 1.76 ‰ and 0.35 ‰, respectively in the MIS 6 and MIS 5e. By comparing the SST records of WEP with the Eastern Equatorial Pacific (EEP) since MIS 6, we find that the Tropical Pacific was more likely in the phase of El Niño -like during Terminations and warming stage in glacial stage (MIS 6). Meanwhile, more water vapor and heat had been transported to dipolar areas. During the Terminations, when the globe was warming, the zonal gradient of tropical pacific and global ice volume decreased. In the warming stage of MIS 6, the zonal gradient was lower, whereas the global ice volume sustained growth, maybe the heat was not enough to promote the melting of glacier at this moment, but the water vapor transport contributed to the glacier building in polars. Due to numerous factors can influence the salinity change, with the results of the comparation of the δ18Osw between the WEP and EEP, we can not draw out the precipitation difference. By comparing the WEP precipitation records from KX97322-4 and MD05-2920 with Chinese cave stalagmite records, we find that the tropical pacific was bound up with the ITCZ changes and even could influence East Asia Monsoon precipitation. When the isolation became stronger, the globe was warming and the WEP precipitation declined and evaporation enhanced, the ITCZ with more moisture shifted from the near equator to the temperate latitude, then the East Asia precipitation was strengthened. Our finding provide new evidence to the relationship between the WEP sea surface water variation and the East Asia precipitation, the Tropical Pacific zonal variation during the global warming and the ITCZ change during the past ca.200ka.