MIS6期以来热带西太平洋降雨与ITCZ的关系

通过Ontong-Java海台KX97322-4孔沉积物中浮游有孔虫表层种Globigerinoides ruber的Mg/Ca海表温度(SST)并结合其 δ18O得到过去约200ka B.P. 以来当地水文(盐度和降雨)指标,结果表明从MIS 6期以来,热带太平洋暖池区温度变化存在明显的冰期-间冰期波动,降温幅度超过3℃.通过与赤道东太平洋对比表明热带太平洋在过去冰消期和冰期中的升温阶段呈现出类 El Niño 的状态,向两极输送水汽和热量.在冰消期,热带太平洋纬向温度梯度降低,全球升温,全球冰量下降.在冰期中升温阶段(MIS 6)热带太平洋纬向温度梯度降低时全球冰量却持续增加,可能此时输送热量不足以使两极冰川融化,带来的水汽又促进了两极冰川的形成.通过与中国石笋记录和热带降雨记录对比,表明热带太平洋纬向温度梯度的变化与热带辐合带(ITCZ)的移动密切相关,并且影响到东亚夏季风的降雨状况,热带太平洋类ENSO过程可能对ITCZ的变化存在内部系统调谐的作用.

THE RELATIONSHIP BETWEEN THE TROPICAL PACIFIC PRECIPITATION AND THE ITCZ VARIATION SINCE MIS 6

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.