Ocean circulation critically affects the global climate and atmospheric carbon dioxide through redistribution of heat and carbon in the Earth system. Despite intensive research, the nature of past ocean circulation changes remains elusive. Here we present deep-water carbonate ion concentration reconstructions for widely distributed locations in the Atlantic Ocean, where low carbonate ion concentrations indicate carbon-rich waters. These data show a low-carbonate-ion water mass that extended northward up to about 20° S in the South Atlantic at 3–4 km depth during the Last Glacial Maximum. In combination with radiocarbon ages, neodymium isotopes and carbon isotopes, we conclude that this low-carbonate-ion signal reflects a widespread expansion of carbon-rich Pacific deep waters into the South Atlantic, revealing a glacial deep Atlantic circulation scheme different than commonly considered. Comparison of high-resolution carbonate ion records from different water depths in the South Atlantic indicates that this Pacific deep-water expansion developed from approximately 38,000 to 28,000 years ago. We infer that its associated carbon sequestration may have contributed critically to the contemporaneous decline in atmospheric carbon dioxide, thereby helping to initiate the glacial maximum.

海洋循环通过热和碳在地球系统中的重新分布，严重影响了全球气候和大气中的二氧化碳。尽管进行了深入研究，但过去海洋环流变化的性质仍然难以捉摸。在这里，我们介绍了大西洋中分布广泛的深水碳酸盐离子浓度重构，其中低碳酸盐离子浓度表示富碳水域。这些数据显示，在最后一次冰河期最大冰期期间，低碳酸盐离子水团在南大西洋以3-4公里的深度向北延伸至约20°S。结合放射性碳时代，钕同位素和碳同位素，我们得出结论，这种低碳离子信号反映了富碳的太平洋深水向南大西洋的广泛扩张，揭示了一种不同于通常认为的冰川深大西洋循环方案。对南大西洋不同深度的高分辨率碳酸盐离子记录的比较表明，这种太平洋深水膨胀发生在大约38,000到28,000年前。我们推断，其相关的碳固存可能对大气中二氧化碳的同期下降起了关键作用，从而有助于引发冰期最大值。