Deep-Atlantic Interhemispheric Water Mass Competition since the Mid-Pleistocene Transition (ODP 1063 versus ODP 1094/1090)

根据佩纳和戈尔茨坦（2014），Dausmann等人（2017），Farmer等人（2019）和Tachikawa等人（2021）的研究，中更新世过渡（MPT）的标志是Nd同位素记录的海洋热盐环流（THC）系统的重大破坏，随后在冰川气候期间再次发生。随后的冰川-间冰期周期性的根本变化清楚地标志着从2082 m和3702 m深度处深海εNd（放射成因143 Nd/144 Nd同位素比值）的微小冰川-间冰期差异到大间冰期-冰川εNd对比的变化。在北大西洋的其他研究证实了系统的冰川间冰期钕同位素模式，反映了南部和北方内部大西洋水团之间的竞争。因此，准确的知识的南北梯度的Nd同位素沿着的流动路径是基本的定量估计水团混合的功能的强度和结构的深水流。在这里，我们定义Δε10为每10°纬度水团对Nd同位素混合的敏感度，即每纬度的半球间梯度。最近的研究和我们的初步工作表明，当把极锋以南的南极环流水包括在平衡中时，南北εNd每10 °纬度的差异（Δε10）为0.6-1.1。长期趋势和显着变化的Nd敏感性可以证明在过去的140 ka。然而，总体而言，由于在寒冷气候期间南大西洋太平洋深水的影响越来越大，因此敏感性非常高。首次发现了距今约110 ka前由于北方冰盖的形成而导致Nd供应减少的影响。在海因里希事件1期间，北大西洋环流的已知扰动被认为使钕敏感度减半（但到目前为止还没有考虑太平洋对平衡的贡献）。因此，为了通过εNd和δ 13 C的联合研究充分捕捉水团起源和深循环强度的变化，需要对Δε10进行超过100万年的高分辨率重建。因此，我们的目标是产生一个时间序列的Nd同位素跨度超过1马在南大西洋，南部的极锋。我们选择ODP 1094进行这项研究，因为我们可以证明在过去的140 ka中，环极水团之间的完美定位。同样，沉积速率很高，时间分辨率可以达到数千年。基于在两年的项目期间产生的大量Nd分析，将对观测结果进行改进，以评估海洋环流和全球CO2脱钩的敏感性变化的影响，以及“不冷不热”间冰期的行为和太平洋沃茨在冰期的推进。

The Mid-Pleistocene Transition (MPT) is marked by a major disruption of the ocean thermohaline circulation (THC) system recorded in Nd isotopes, which subsequently reoccurs during glacial climates, according to studies by Pena and Goldstein (2014), Dausmann et al. (2017), Farmer et al. (2019) and Tachikawa et al. (2021). The subsequent fundamental change in glacial-interglacial periodicity clearly marks a change from minor glacial-interglacial differences in deep ocean εNd (radiogenic 143Nd/144Nd – isotope ratios) at 2082 m and 3702 m depth to large interglacial-glacial εNd contrasts. Other studies in the North Atlantic confirm systematic glacial–interglacial Nd-isotope pattern reflecting the competition between southern and northern interior Atlantic water masses. Thus, accurate knowledge of the north-south gradient of Nd isotopy along the flow path is fundamental to quantitatively estimate water mass mixing as a function of the strength and structure of deep water flow. Here we define Δε10 as the sensitivity of water masses to Nd-isotope mixing per 10° latitude, i.e. the interhemispheric gradient per latitude. Recent studies and our preliminary work show a north-south εNd difference per 10 ° latitude (Δε10) of 0.6-1.1 when Circum Antarctic Current water south of the polar front is included in the balance. Long-term trends and dramatic changes in Nd - sensitivity could be demonstrated for the past 140 ka. Overall, however, the sensitivity is very high due to the increasing influence of Pacific deep water in the South Atlantic during cold climate. First evidence was collected on the influences of reduced Nd supply due to the formation of northern hemispheric ice sheets around 110 ka before present. Known perturbations of the North Atlantic circulation during Heinrich Event 1 are thought to halve the Nd sensitivity (but so far without considering a Pacific contribution to the balance). Thus, in order to fully capture changes in water mass origin and deep circulation strength through combined studies of εNd and δ13C, a high-resolution reconstruction of Δε10 is required over more than 1 million years. The goal is therefore to generate a time series of Nd isotopy spanning more than 1 Ma in the South Atlantic, south of the polar front. We selected ODP 1094 for this study because we can demonstrate perfect positioning between circumpolar water masses for the last 140ka. Similarly, sedimentation rates are high, allowing temporal resolution of millennia. Based on a large number of Nd analyses generated over the project duration of two years, the observations will be refined to assess the impact of changing sensitivity to the decoupling of ocean circulation and global CO2, as well as the behavior of "lukewarm" interglacials and the advance of Pacific waters during glacial periods.