The chain of events surrounding the initiation and intensification of the last glacial cycle remain relatively poorly understood. In particular, the role of Southern Ocean paleocirculation changes is poorly constrained, in part, owing to a paucity of sedimentary records from this region. In this study we present multiproxy data – including neodymium isotope and sortable silt measurements – for paleocirculation changes within the deep (3167 m water depth) Indian sector of the Southern Ocean from a new sediment core, TT1811-34GGC (41.718°S, 80.163°E). We find a tight coupling between circulation changes, Antarctic climate, and atmospheric CO₂ concentrations throughout the last 118,000 years, even during the initial stages of glacial inception of Marine Isotope Stage (MIS) 5.4 to 5.1. We find that periods of cooling correspond to reductions in the entrainment of North Atlantic-sourced waters within the deep Southern Ocean, as evidenced by more radiogenic neodymium isotope values of deep water bathing our core site. Cooling also corresponds to generally slower bottom water flow speeds, as indicated by finer sortable silt size fractions. A reduction in entrainment of North-Atlantic sourced waters occurred during MIS 5.4–5.1, when Atlantic circulation was strong, suggesting a Southern hemisphere control on paleocirculation changes at that time. We hypothesise that expanded Southern Ocean sea-ice during MIS 5.4 increased the density of the deep Southern Ocean, reducing the ability of Atlantic-sourced waters to mix into Lower Circumpolar Deep Water. This led to an expanded contribution of Pacific Deep Water within the lower circulation cell and increased stratification within the deep Southern Ocean. These paleocirculation changes can help account for the reduction in atmospheric CO₂ across the MIS 5.5 to 5.4 transition, and in doing so help explain the chain of events surrounding the decent into the last glacial period.

围绕最后一个冰川周期的开始和加剧的事件链仍然知之甚少。特别是，南洋古环流变化的作用受到制约很有限，部分原因是该地区的沉积记录很少。在这项研究中，我们介绍了新代理沉积物TT1811-34GGC（41.718°S，80.163°）在南大洋深部（水深3167 m）的印度洋扇段内古循环变化的多重代理数据（包括钕同位素和可分类的粉砂测量）。 E）。我们发现环流变化，南极气候和大气CO ₂之间存在紧密的联系在过去的118,000年中，甚至在海洋同位素阶段（MIS）5.4至5.1的冰期初期，其浓度都很高。我们发现，冷却期对应于南大洋深部北大西洋水域的夹带量减少，深水浸入我们核心地点的放射性同位素钕同位素值证明了这一点。冷却还对应于通常较慢的底部水流速度，如较细的可分类淤泥粒度分数所示。在MIS 5.4-5.1期间，大西洋环流旺盛，北大西洋水域的夹带量减少，这表明当时南半球对古环流变化的控制。我们假设在MIS 5.4期间扩展了南大洋海冰，从而增加了深海的密度，降低源自大西洋的水混入下极地极深水的能力。这导致太平洋深水在下部循环单元内的贡献增加，并增加了深海南部的分层。这些古循环变化可以帮助解释大气中CO的减少₂从MIS 5.5过渡到5.4的过程中，这样做有助于解释围绕体面进入上一个冰河期的一系列事件。