Over the past three million years, Earth’s climate oscillated between warmer interglacials with reduced terrestrial ice volume and cooler glacials with expanded polar ice sheets. These climate cycles, as reflected in benthic foraminiferal oxygen isotopes, transitioned from dominantly 41-kyr to 100-kyr periodicities during the mid-Pleistocene 1,250 to 700 kyr ago (ka). Because orbital forcing did not shift at this time, the ultimate cause of this mid-Pleistocene transition remains enigmatic. Here we present foraminiferal trace element (B/Ca, Cd/Ca) and Nd isotope data that demonstrate a close linkage between Atlantic Ocean meridional overturning circulation and deep ocean carbon storage across the mid-Pleistocene transition. Specifically, between 950 and 900 ka, carbonate ion saturation decreased by 30 µmol kg⁻¹ and phosphate concentration increased by 0.5 µmol kg⁻¹ coincident with a 20% reduction of North Atlantic Deep Water contribution to the abyssal South Atlantic. These results demonstrate that the glacial deep Atlantic carbon inventory increased by approximately 50 Gt during the transition to 100-kyr glacial cycles. We suggest that the coincidence of our observations with evidence for increased terrestrial ice volume reflects how weaker overturning circulation and Southern Ocean biogeochemical feedbacks facilitated deep ocean carbon storage, which lowered the atmospheric partial pressure of CO₂ and thereby enabled expanded terrestrial ice volume at the mid-Pleistocene transition.

在过去的三百万年中，地球气候在陆地冰量减少的较温暖的冰层间和极地冰原扩展的较冷的冰层之间振荡。如底栖有孔虫的氧同位素所反映的那样，这些气候周期在中新世1,250至700年前（ka）从占主导地位的41-kyr过渡到了100-kyr。由于此时的轨道强迫没有发生变化，因此这种中更新世过渡的最终原因仍然是未知的。在这里，我们介绍有孔虫痕量元素（B / Ca，Cd / Ca）和Nd同位素数据，这些数据表明大西洋子午翻转翻转循环和中更新世过渡期间深海碳储存之间的紧密联系。具体而言，在950至900 ka之间，碳酸根离子饱和度降低了30 µmol kg ^-1磷酸盐浓度增加了0.5 µmol kg ^-1，同时北大西洋深水对深渊南大西洋的贡献减少了20％。这些结果表明，在向100千瓦的冰川循环过渡期间，冰川深部大西洋的碳存量增加了约50 Gt。我们认为，我们的观测结果与陆地冰量增加的证据相吻合，反映出翻转的环流减弱和南大洋生物地球化学反馈如何促进深海碳储存，从而降低了CO ₂的大气分压，从而使中部陆地冰量得以扩大-更新世过渡。