(Table S1) Diatom abundance according to ice cycles in ANDRILL AND1-1B drill core@en

The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5°C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world.由于缺乏定年精准的南极近源古环境记录，南极与南大洋对上新世晚期全球气候重建的影响始终不明朗。本研究基于从罗斯冰架下方获取的ANDRILL AND-1B沉积岩芯，报道了冰盖、海表温度与海冰的重建结果。我们的证据显示，罗斯海区域的冰盖在约3.3 Ma时发生大规模扩张，随后沿岸海表温度下降约2.5℃，海冰逐步扩张，并在3.3 Ma至2.5 Ma期间于罗斯海出现冰间湖式深层混合。南极降温的加剧使得西风环流增强，海洋环流得以活化。与之伴随的南大洋锋面向北迁移，通过限制不同海盆间的表层水连通性，与大西洋经向翻转环流（Atlantic Meridional Overturning Circulation）的减弱相关联，这对向北大西洋高纬度区域的热量输送具有启示意义。尽管本研究结果并未排除低纬度机制作为上新世降温的驱动因素，但它们表明，在双极气候格局形成过程中，南半球高纬度降温发挥了额外的作用。