Sea surface temperature estimates and alkenone C37:4 abundances in ODP Site 145-882 and 177-1090

The cold upwelling 'tongue' of the eastern equatorial Pacific is a central energetic feature of the ocean, dominating both the mean state and temporal variability of climate in the tropics and beyond. Recent evidence for the development of the modern cold tongue during the Pliocene-Pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline. We have found that the sub-Antarctic and sub-Arctic regions underwent substantial cooling nearly synchronous to the cold tongue development, thereby providing support for this hypothesis. In addition, we show that sub-Antarctic climate changed in its response to Earth's orbital variations, from a subtropical to a subpolar pattern, as expected if cooling shrank the warm-water sphere of the ocean and thus contracted the subtropical gyres.

东赤道太平洋冷上升流舌状区是海洋核心动力特征之一，主导热带及全球海域的气候平均态与时间变异性。近年来，有证据表明现代冷舌状区在上新世-更新世过渡期逐步形成，该现象被归因于外热带冷却驱动温跃层（thermocline）变浅。本研究发现，亚南极（sub-Antarctic）与亚北极（sub-Arctic）区域经历了显著冷却过程，其发生时间与冷舌状区形成几乎同步，为上述假说提供了支撑。此外，本研究表明亚南极气候响应地球轨道参数变化的模式已从副热带型转变为副极地型——若冷却作用缩小了海洋暖水圈范围、进而收缩副热带环流（subtropical gyres），该转变恰与预期结果相符。