Little Change in Ice Age Water Mass Structure From Cape Basin Benthic Neodymium and Carbon Isotopes
Little Change in Ice Age Water Mass Structure From Cape Basin Benthic Neodymium and Carbon Isotopes
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DOI：
10.1029/2021pa004281
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发表时间：
2021-10
影响因子：
3.5
通讯作者：
S. Hines;L. Bolge;S. Goldstein;C. Charles;I. Hall;S. Hemming
中科院分区：
文献类型：
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作者：
S. Hines;L. Bolge;S. Goldstein;C. Charles;I. Hall;S. Hemming
关于冰河时期深海的一个普遍概念是，与今天相比，大西洋上层环流圈在末次盛冰期变浅，并且这种构造有利于深海中碳储存的增加，从而导致冰川期二氧化碳含量下降。在此，我们在遥远的南大西洋对这一观点进行检验，通过对国际大洋发现计划U1479站点（位于开普盆地水深2615米处）的钕和底栖碳同位素配对测量来研究冰川环流结构的变化。我们通过将我们的站点与开普盆地其他现有的碳和钕同位素记录进行比对，研究垂直同位素梯度，同时确定不同深度推断的环流变化的相对时间，从而推断出上一个冰川旋回中环流结构的变化。我们发现，在分析的站点中，U1479站点在上一个冰川旋回中具有最负的钕同位素组成，这表明该深度在间冰期和冰期都受到北大西洋深层水（NADW）的强烈影响。这一观测结果排除了北大西洋深层水在约2000米以上大幅变浅的假设。然而，我们的证据表明，在上一个冰川旋回中，中深层和深海站点之间的分层更加明显，这种情况在海洋同位素阶段5就已形成。尽管中深层海洋结构变化不大，但这些条件可能仍然对深海中的冰川碳储存有贡献。
A common conception of the deep ocean during ice age episodes is that the upper circulation cell in the Atlantic was shoaled at the Last Glacial Maximum compared to today, and that this configuration facilitated enhanced carbon storage in the deep ocean, contributing to glacial CO2 draw‐down. Here, we test this notion in the far South Atlantic, investigating changes in glacial circulation structure using paired neodymium and benthic carbon isotope measurements from International Ocean Discovery Program Site U1479, at 2,615 m water depth in the Cape Basin. We infer changes in circulation structure across the last glacial cycle by aligning our site with other existing carbon and neodymium isotope records from the Cape Basin, examining vertical isotope gradients, while determining the relative timing of inferred circulation changes at different depths. We find that Site U1479 had the most negative neodymium isotopic composition across the last glacial cycle among the analyzed sites, indicating that this depth was most strongly influenced by North Atlantic Deep Water (NADW) in both interglacial and glacial intervals. This observation precludes a hypothesized dramatic shoaling of NADW above ∼2,000 m. Our evidence, however, indicates greater stratification between mid‐depth and abyssal sites throughout the last glacial cycle, conditions that developed in Marine Isotope Stage 5. These conditions still may have contributed to glacial carbon storage in the deep ocean, despite little change in the mid‐depth ocean structure.