(Table 1) Age comparison between the GPTS and ODP Site 181-1123 age model for each chron base within the Middle Miocene section

Today the deep western boundary current (DWBC) east of New Zealand is the most important route for deep water entering the Pacific Ocean. Large-scale changes in deep water circulation patterns are thought to have been associated with the development of the East Antarctic Ice Sheet (EAIS) close to the main source of bottom water for the DWBC. Here we reconstruct the changing speed of the southwest Pacific DWBC during the middle Miocene from ~15.5-12.5 Ma, a period of significant global ice accumulation associated with EAIS growth. Sortable silt mean grain sizes from Ocean Drilling Program Site 1123 reveal variability in the speed of the Pacific inflow on the timescale of the 41 kyr orbital obliquity cycle. Similar orbital period flow changes have recently been demonstrated for the Pleistocene epoch. Collectively, these observations suggest that a strong coupling between changes in the speed of the deep Pacific inflow and high-latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 Myr. Furthermore, long-term changes in flow speed suggest an intensification of the DWBC under an inferred increase in Southern Component Water production. This occurred at the same time as decreasing Tethyan outflow and major EAIS growth between ~15.5 and 13.5 Ma. These results provide evidence that a major component of the deep thermohaline circulation was associated with the middle Miocene growth of the EAIS and support the view that this time interval represents an important step in the development of the Neogene icehouse climate.如今，新西兰以东的西边界深层流（deep western boundary current, DWBC）是深层水进入太平洋的核心通道。学界普遍认为，深层水循环格局的大规模变化，与紧邻西边界深层流底层水主要源区的东南极冰盖（East Antarctic Ice Sheet, EAIS）的演化密切相关。本研究重建了中新世中期（约15.5~12.5 Ma）西南太平洋西边界深层流的流速变化历史——该时期为全球冰量显著累积、东南极冰盖持续扩张的阶段。取自大洋钻探计划（Ocean Drilling Program, ODP）1123站位的可分选粉砂平均粒径数据显示，太平洋入流流速的变化在41千年尺度的轨道斜度周期（orbital obliquity cycle）上呈现显著波动。近期研究已证实，更新世亦存在类似的轨道周期尺度的流速变化。综合来看，这些观测结果表明，太平洋深层入流流速变化与高纬度气候强迫之间的强耦合关系，至少在过去15百万年（Myr）以来，始终是全球温盐环流（thermohaline circulation）系统的稳定特征之一。此外，流速的长期变化特征显示，在推断的南部组分水团（Southern Component Water）生成量增加的背景下，西边界深层流出现了增强现象。这一变化发生在约15.5~13.5 Ma期间，与特提斯洋流出流（Tethyan outflow）减弱以及东南极冰盖大规模扩张的时间完全重合。本研究结果证实，深层温盐环流的主要分支与中新世中期东南极冰盖的扩张存在关联，同时也支持这一观点：该时段是新近纪冰室气候（Neogene icehouse climate）演化进程中的关键阶段。