Abstract The oceanic thermocline circulation provides a route of communication between the surface and deep ocean and could have played an important role in the global carbon cycle, but studies on reconstructing past thermocline water properties are limited. Here we explore the potential use of left-coiling Globorotalia truncatulinoides as a recorder of thermocline conditions by measuring the stable oxygen and carbon isotopic compositions of this species from 28 surface sediments in the southwest Pacific near New Zealand. Our data show that G. truncatulinoides (sinistral) calcify mainly in the range of subsurface/thermocline depths in this study region between 100 and 850 m with their carbon isotopes largely corresponding to the surrounding seawater values. To understand the controlling factors of the thermocline δ13C evolution in the South Pacific, a 260 ka downcore δ13C record on this species (δ13CG.trunc) from core site ODP1123 is presented and compared with other δ13C records. The convergence of δ13C from thermocline, upper and lower circumpolar deep waters (UCDW/LCDW) during glacial terminations indicates that the deep ocean is the predominant source of increased atmospheric pCO2 and the δ13C anomalies in the upper ocean and atmosphere during the deglacials. This is evident in both the South Pacific and South Atlantic. A quantitative calculation of predicted surface ocean δ13C based on thermodynamic air-sea equilibrium implies this process has a significant control on the temporal thermocline water δ13C variation over the last glacial-interglacial (G-I) cycle. The lower deglacial δ13CG.trunc values in the South Atlantic compared to the Pacific further suggest a stronger upwelling in the Atlantic sector of the Southern Ocean, indicating that this was a major ventilation route with an important stock of light δ13C from the deep waters of this region. This study demonstrates the deep water influence (via upwelling) and atmospheric carbon isotope imprint (via air-sea exchange) on thermocline water δ13C evolution. It also provides important evidence for the rapid exchange of carbon between the Southern Ocean and atmosphere over multiple G-I cycles.

中文翻译：

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过去 260 ka 南大洋与大气之间稳定碳同位素的耦合演化

摘要 大洋温跃层环流提供了表层和深海之间的沟通途径，可能在全球碳循环中发挥重要作用，但重建过去温跃层水特性的研究有限。在这里，我们通过测量新西兰附近西南太平洋 28 个表层沉积物中该物种的稳定氧和碳同位素组成，探索左旋 Globorotalia truncatulinoides 作为温跃层条件记录器的潜在用途。我们的数据显示，G. truncatulinoides (sinistral) 主要在该研究区域 100 至 850 m 之间的地下/温跃层深度范围内钙化，其碳同位素在很大程度上对应于周围的海水值。为了了解南太平洋温跃层 δ13C 演化的控制因素，提出了来自核心站点 ODP1123 的该物种 (δ13CG.trunc) 的 260 ka 下行 δ13C 记录，并与其他 δ13C 记录进行了比较。冰川终止期间温跃层、上、下环极深水 (UCDW/LCDW) δ13C 的收敛表明，深海是冰消期期间大气 pCO2 增加和上层海洋和大气中 δ13C 异常的主要来源。这在南太平洋和南大西洋都很明显。基于热力学海气平衡预测的表层海洋 δ13C 的定量计算表明，该过程对上次冰期-间冰期 (GI) 循环中温跃层水 δ13C 的时间变化具有显着控制。下冰期δ13CG。与太平洋相比，南大西洋的 trunc 值进一步表明南大洋的大西洋部分有更强的上升流，表明这是一条主要的通风路线，拥有来自该地区深水的重要光 δ13C。这项研究证明了深水影响（通过上升流）和大气碳同位素印记（通过海气交换）对温跃层水 δ13C 演化的影响。它还为南大洋和大气之间在多个 GI 循环中快速交换碳提供了重要证据。这项研究证明了深水影响（通过上升流）和大气碳同位素印记（通过海气交换）对温跃层水 δ13C 演化的影响。它还为南大洋和大气之间在多个 GI 循环中快速交换碳提供了重要证据。这项研究证明了深水影响（通过上升流）和大气碳同位素印记（通过海气交换）对温跃层水 δ13C 演化的影响。它还为南大洋和大气之间在多个 GI 循环中快速交换碳提供了重要证据。