(Appendix A) Sea surface temperature reconstruction for ODP Site 184-1143@en

Orbital resolution thermal histories over the last 4 Ma at ODP Site 1143 in the tropical western Pacific are reconstructed using alkenone paleothermometry. The temperature profile is characterized by a steady state of ~29 °C with fluctuations < 1 °C before 2.7 Ma and by a strong oscillating state from 2.7 Ma, largely due to cooling by up to 4 °C from ~29 °C in interglacial to 26 °C in glacial intervals. This implies a relative warm and stable surface hydrography during the early and mid Pliocene in this region influenced by the warm pool before temperature decreases in responding to global cooling and the formation of the distinct glacial stages since the late Pliocene. Therefore, the smaller SST gradient between tropical eastern and western Pacific and between southern and northern South China Sea before the late Pliocene indicates a super sized Pliocene Pacific warm pool, while the larger SST gradient since then marks progressively intensification of the zonal Walker circulation and meridional Hadley circulation, representing the monsoon circulations in the region. The intensification of the Walker and Hadley circulations over the tropical Pacific may also have helped on the onset of glaciations and subsequent deglaciations during the late Pliocene and Pleistocene.基于热带西太平洋大洋钻探计划（Ocean Drilling Program, ODP）1143站位的岩芯记录，利用烯酮古温标法（alkenone paleothermometry）重建了过去4 Ma的轨道尺度热演化历史。该温度序列的演化特征可分为两个阶段：2.7 Ma之前，其以约29℃为稳定态，波动幅度小于1℃；2.7 Ma之后则转为强振荡状态，冰期时段海表温度较间冰期的约29℃最多降温4℃，降至26℃。这表明，上新世（Pliocene）早中期，该区域受西太平洋暖池影响，海表水文环境相对温暖且稳定；直至上新世晚期，全球变冷驱动温度下降，且形成了清晰的冰期旋回，这一稳定状态才被打破。因此，上新世晚期之前，热带东-西太平洋以及南海南北海域间的海表温度（Sea Surface Temperature, SST）梯度较小，这指示上新世时期存在超大规模的太平洋暖池；而自此之后SST梯度逐步增大，则标志着纬向沃克环流（Walker circulation）与经向哈德利环流（Hadley circulation）持续增强，二者共同构成了该区域的季风环流系统。热带太平洋沃克环流与哈德利环流的增强，同样可能促进了上新世晚期至更新世（Pleistocene）时期冰期的启动与后续的冰消过程。