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

根据Pena和Goldstein(2014)，Dausmann等人的研究，中更新世过渡(MPT)的标志是由ND同位素记录的海洋温盐环流(THC)系统的重大破坏，随后在冰川气候期间再次发生。(2017)，Farmer等人。(2019)和Tchikawa等人。(2021年)。随后的冰期-间冰期周期性的根本变化明显地标志着从2082m和3702m深的深海εNd(放射性成因的143Nd/144Nd同位素比值)的小的冰期-间冰期差异到大的间冰期-冰期εNd的对比。北大西洋的其他研究证实了系统的冰川-间冰期ND同位素模式，反映了大西洋南部和北部内陆水团之间的竞争。因此，准确了解沿流动路径的ND同位素南北梯度是定量估计作为深水流动强度和结构函数的水团混合的基础。这里我们将Δε10定义为水团对每10°纬度的ND同位素混合的敏感性，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，当极锋以南的环南极流水包括在平衡中时，每10°纬度(ε10)的南北ΔεND差为0.6-1.1.在过去的140ka，ND敏感性的长期趋势和剧烈变化可以被证明。然而，总的来说，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，所以敏感性很高。首次收集了110ka以前北半球冰盖形成导致的ND供应减少的影响的证据。海因里希事件1期间北大西洋环流的已知扰动被认为使ND敏感性减半(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δ13C的联合研究完全捕捉到水团来源和深部环流强度的变化，需要在100多万年内对Δε10进行高分辨率重建。因此，目标是在极锋以南的南大西洋产生一个跨度超过1 Ma的Nd同位素时间序列。我们选择ODP1094进行这项研究，是因为我们可以证明在过去140ka的环极水团之间的完美定位。同样，沉积速率很高，可以实现数千年的时间分辨率。在项目为期两年的大量ND分析的基础上，将改进观测，以评估对海洋环流和全球二氧化碳脱钩的敏感性变化的影响，以及“不温”间冰川的行为和冰期期间太平洋水域的推进。

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.