Sea surface temperature calculated from UK37 and UK'37 in the Pacific sector of the Southern Ocean@en

In spite of the important role played by the Southern Ocean in global climate, the few existing paleoceanographic records in the east Pacific sector do not extend beyond one glacial-interglacial cycle, hindering circumpolar comparison of past sea surface temperature (SST) evolution in the Southern Ocean. Here we present three alkenone-based Pleistocene SST records from the subantarctic and subtropical Pacific. We use a regional core top calibration data set to constrain the choice of calibrations for paleo SST estimation. Our core top data confirm that the alkenone-based UK37 and UK'37 values correlate linearly with the SST, in a similar fashion as the most commonly used laboratory culture-based calibrations even at low temperatures (down to ~1°C), rendering these calibrations appropriate for application in the subantarctic Pacific. However, these alkenone indices yield diverging temporal trends in the Pleistocene SST records. On the basis of the better agreement with d18O records and other SST records in the subantarctic Southern Ocean, we propose that the UK37 is a better index for SST reconstruction in this region than the more commonly used UK'37 index. The UK37-derived SST records suggest glacial cooling of ~8°C and ~4°C in the subantarctic and subtropical Pacific, respectively. Such extent of subantarctic glacial cooling is comparable to that in other sectors of the Southern Ocean, indicating a uniform circumpolar cooling during the Pleistocene. Furthermore, our SST records also imply massive equatorward migrations of the Antarctic Circumpolar Current (ACC) frontal systems and an enhanced transport of ACC water to lower latitudes during glacials by the Peru-Chile Current.尽管南大洋（Southern Ocean）在全球气候系统中扮演着关键角色，但东太平洋海域现存的古海洋学记录极少能覆盖超过一个冰期-间冰期循环，这极大阻碍了针对南大洋过去海表温度（sea surface temperature, SST）演化开展环大洋对比研究。本文报道了3条基于烯酮（alkenone）的太平洋亚极地与亚热带海域更新世海表温度记录。我们采用区域表层岩心校准数据集来约束古海表温度估算所用的校准模型。我们的表层岩心数据证实，基于烯酮的UK₃₇与UK’₃₇指标与海表温度呈线性相关，即便在低至约1℃的低温环境下，其相关性模式也与最常用的实验室培养校准方法高度一致，表明这些校准模型适用于太平洋亚极地海域。然而，这两类烯酮指标在更新世海表温度记录中呈现出分歧的时间演化趋势。结合与南大洋亚极地海域δ¹⁸O记录及其他海表温度记录的更高吻合度，我们认为相较于更常用的UK’₃₇指标，UK₃₇更适合该区域的海表温度重建。基于UK₃₇得到的海表温度记录显示，太平洋亚极地与亚热带海域的冰期降温幅度分别约为8℃与4℃。亚极地海域的冰期降温幅度与南大洋其他海域相当，表明更新世期间存在统一的环大洋降温过程。此外，我们的海表温度记录还表明，冰期时期南极绕极流（Antarctic Circumpolar Current, ACC）锋面系统发生了大规模向赤道迁移，且秘鲁-智利海流强化了南极绕极流水体向低纬度的输送。