Analysis and interpretation of Tritium and Helium tracer data collected in the North Pacific in 2015.

通过跟踪水柱上两公里处瞬态示踪剂的演变，可以记录温跃层通风的变化，特别是亚热带和赤道地区之间的内部环流路径。这些环流细胞被认为对包括ENSO在内的主要气候现象作出反应并在调节/维持这些气候现象中发挥重要作用，并且还与太平洋年代际振荡有关。此外，有越来越多的证据表明，这些环流细胞的强度在十年时间尺度上发生了变化，这可能在更大的尺度上对气候产生重大影响。瞬态示踪剂突出了新通风的水进入海洋的途径。它们的时间演化分布为水团形成速率和循环以及生物地球化学过程速率提供了定量约束。氚是一种有价值的瞬态示踪剂，因为它具有独特的时间历史和边界条件，可以产生比其他示踪剂更多的信息。此外，它的子代氦-3提供了额外的、独特的信息，因为它具有与所有其他瞬态示踪剂互补的（类似营养物的）边界条件。将时间序列扩展到更长的时间，既可以描述更长的时间尺度通风过程，又可以诊断短时间尺度过程中的时间变化。此外，氚分布的空间梯度减小和时间导数的减小进一步减小了氚/氦-3年龄的非线性行为。通过重新占领关键的水文剖面，观察这些示踪剂的演变分布将为海洋环流和通风的理论和模式提供有力的约束。处理后的数据集将存档，并通过已建立的数据中心公开提供。参与模拟海洋环流、通风和气候变化的各种研究企业都可以获得这些数据。示踪剂，特别是放射性和瞬态示踪剂（如氯氟烃、放射性碳、氚/氦-3），已成为世界海洋环流实验（WOCE）和气候变率和可预测性计划（CLIVAR）水文计划的组成部分，是研究海洋通风及其在气候尺度上变化的宝贵工具。认识到全球变化已经对海洋产生了影响，CLIVAR计划试图从2003年开始，每隔大约十年的时间尺度重新占据海洋的关键区域。该项目的主要目标是记录瞬态示踪剂氚和氦-3在WOCE占领24年来分布的时间演变，并利用这些信息诊断太平洋浅层温跃层通风和经向翻转的变化率。此外，这些示踪剂在不直接在北太平洋露头的密度层上的长期演化可能对混合过程对这些密度层通风的影响提供有用的限制。研究人员将分析和解释2015年占领北太平洋中部P16N部分获得的样品的氦同位素和氚测量值，该部分穿过北部亚极地和亚热带环流以及北部和南部热带。

By following the evolution of transient tracers in the upper two kilometers of the water column, it is possible to document changes in thermocline ventilation, in particular the interior circulation pathways between the subtropics and the equatorial region. These circulation cells have been argued to respond to and play an important role in modulating/maintaining major climatic phenomena, including ENSO, and are also relevant to the Pacific Decadal Oscillation. Moreover, there is mounting evidence of decade-timescale changes in the strength of these circulation cells which may have significant climate impacts on even larger scales. Transient tracers highlight the pathways of newly ventilated water into the ocean. Their time-evolving distributions provide quantitative constraints on water mass formation rates and circulation, and the rates of biogeochemical processes. Tritium is a valuable transient tracer because it has a distinctive time history and boundary condition that yields additional information to other tracers. Moreover, its daughter Helium-3 provides additional, unique information because of its complementary (nutrient-like) boundary conditions to all other transient tracers. Extending the time series to longer times provides a description of both longer time-scale ventilation processes and the opportunity to diagnose time variations in the short time-scale processes. Additionally, the evolution toward smaller spatial gradients in the tritium distribution and reduced time derivatives further minimizes non-linear behavior in the tritium/Helium-3 age. Through the reoccupation of key hydrographic sections, observation of the evolving distributions of these tracers will provide powerful constraints on theories and models of ocean circulation and ventilation. The processed data set will be archived and made publicly available through established data centers.. This data will be accessible to a wide range of research enterprises involved in modelling ocean circulation, ventilation, and climate change. Tracers, and in particular radioactive and transient tracers (e.g., chlorofluorocarbons, radiocarbon, tritium/Helium-3), have been integral to both the WOCE (World Ocean Circulation Experiment) and CLIVAR (CLImate VARiability and predictability program) hydrographic programs and are valuable tools for studying ocean ventilation and its variations on climatic scales. Recognizing that global change is already affecting the oceans, the CLIVAR program has sought to re-occupy key WOCE sections at roughly decade time-scale intervals since2003. The primary objectives of this project are to document the temporal evolution of the distributions of the transient tracers tritium and Helium-3 over the 24 years since the WOCE occupation, and to use this information to diagnose the changing rates of thermocline ventilation and meridional overturning in the shallow Pacific Ocean. Moreover, the longer term evolution of these tracers on density horizons that do not directly outcrop in the North Pacific may provide useful constraints on the effect of mixing processes on ventilation of those density horizons. The investigators will analyze and interpret helium isotope and tritium measurements on samples acquired on the 2015 occupation of the P16N section in the central North Pacific that crosses the northern subpolar and subtropical gyres as well as the northern and southern tropics.