The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland–Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO₂ to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica.

据认为，北大西洋深水形成的发生与大约3400万年前的南极冰盖生长相吻合（Ma）。然而，这一时机存在争议，部分原因是对北大西洋深部形成的古代北部成分水（NCW）的地球化学特征存在疑问。在这里，我们介绍了位于深水形成地点附近的北大西洋沉积物岩心的详细地球化学记录。我们发现，在36 Ma之前，西北大西洋是分层的，营养丰富，盐分含量低。这个受限制的盆地转变成NCW的管道，该管道在南极冰河初期就开始向南流动约一百万年。可能的触发因素是北极北极海域的构造调整，从而增加了格陵兰-苏格兰海岭之间的交换。表面盐度和密度的增加增强了NCW的生产。由于北冰洋的化石碳泄漏，晚始新世深水团的碳同位素特征与现代价值不同。出口这种富含营养的水提供了CO的瞬态脉冲₂可能是造成短期变暖的地球系统，而增强NCW形成的长期影响是使南极洲冷却的更大的北向热传输。