Abstract Marine Isotope Stage (MIS) M2, 3.3 Ma, is an isolated cold stage punctuating the benthic oxygen isotope (δ18O) stratigraphy of the warm Piacenzian interval of the late Pliocene Epoch. The prominent (∼0.65‰) δ18O increase that defines MIS M2 has prompted debate over the extent to which it signals an early prelude to the rhythmic extensive glaciations of the northern hemisphere that characterise the Quaternary and raised questions about the forcing mechanisms responsible. Recent work suggests that CO2 storage in the deep Atlantic Ocean played an important role in these events but detailed reconstructions of deep ocean chemical stratification are needed to test this idea and competing hypotheses. Here we present new records of the Nd isotope composition of fish debris and δ13C and B/Ca ratios of benthic foraminifera from the northwest and southeast Atlantic Ocean. Our novel geochemical data show that, in contrast to major Quaternary glaciations such as MIS 2 (∼21 ka) and MIS 100 (∼2.52 Ma), the deep North Atlantic Ocean was weakly chemically stratified during MIS M2. We show that Southern Component Water incursion into the Atlantic Ocean was limited to the deep South Atlantic basin during MIS M2 and peaked well before (∼10-15-kyr) the atmospheric CO2 minimum. Our findings imply that the deep Atlantic Ocean was not the principle sink of CO2 sequestered from the atmosphere during MIS M2, implicating a different CO2 storage deep-water reservoir mechanism, presumably Southern Component Water incursion into the Pacific Ocean. Weak chemical stratification in the deep Atlantic Ocean during MIS M2 relative to MIS 100 and 2 suggests comparatively active Atlantic meridional overturning circulation. That suggestion is consistent with the warmth of the high latitude North Atlantic during MIS M2 – surface water temperatures cooled during M2 but only close to Holocene values. Our findings may help to explain the paucity of evidence for extensive early glaciation of the northern hemisphere during M2 but leave open the possibility of ice sheet advance on Antarctica.

中文翻译：

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大约 330 万年前上新世晚期海洋同位素阶段 M2 期间大西洋的气候和深海环流

摘要 海洋同位素阶段 (MIS) M2, 3.3 Ma，是一个孤立的冷阶段，穿插上新世晚期暖皮亚琴阶间隔的底栖氧同位素 (δ18O) 地层。定义 MIS M2 的显着 (~0.65‰) δ18O 增加引发了关于它在多大程度上标志着北半球有节奏的广泛冰川的早期前奏的争论，这是第四纪的特征，并提出了有关负责的强迫机制的问题。最近的工作表明，大西洋深处的二氧化碳储存在这些事件中发挥了重要作用，但需要对深海化学分层进行详细的重建来检验这一想法和相互竞争的假设。在这里，我们展示了来自大西洋西北部和东南部的鱼类碎片的 Nd 同位素组成以及底栖有孔虫的 δ13C 和 B/Ca 比率的新记录。我们新的地球化学数据表明，与 MIS 2 (~21 ka) 和 MIS 100 (~2.52 Ma) 等主要第四纪冰川相比，北大西洋深部在 MIS M2 期间化学分层较弱。我们表明，在 MIS M2 期间，南部成分水侵入大西洋仅限于南大西洋深海盆地，并且在大气 CO2 最小值之前（~10-15-kyr）达到峰值。我们的研究结果表明，深大西洋不是 MIS M2 期间从大气中隔离的 CO2 的主要汇，这意味着不同的 CO2 储存深水储层机制，可能是南部成分水侵入太平洋。相对于 MIS 100 和 2，MIS M2 期间大西洋深部的化学分层较弱，表明大西洋经向翻转环流相对活跃。该建议与 MIS M2 期间高纬度北大西洋的温暖是一致的——地表水温在 M2 期间冷却但仅接近全新世值。我们的研究结果可能有助于解释在 M2 期间北半球广泛早期冰川作用的证据不足，但仍保留南极洲冰盖推进的可能性。该建议与 MIS M2 期间高纬度北大西洋的温暖是一致的——地表水温在 M2 期间冷却但仅接近全新世值。我们的研究结果可能有助于解释在 M2 期间北半球广泛早期冰川作用的证据不足，但仍保留南极洲冰盖推进的可能性。该建议与 MIS M2 期间高纬度北大西洋的温暖是一致的——地表水温在 M2 期间冷却但仅接近全新世值。我们的研究结果可能有助于解释在 M2 期间北半球广泛早期冰川作用的证据不足，但仍保留南极洲冰盖推进的可能性。