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

2015 年在北太平洋收集的氚和氦示踪数据的分析和解释。

• 批准号: 1536384
• 负责人: Scott Doney
• 金额: $ 42.18万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536384&HistoricalAwards=false
• 关键词: Analysis; interpretation; Tritium; Helium; tracer

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.

通过跟踪水柱上部两公里处瞬变示踪物的演变，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。这些环流圈被认为对包括厄尔尼诺/南方涛动在内的主要气候现象作出反应，并在调节/维持这些气候现象方面发挥重要作用，而且还与太平洋十年涛动有关。此外，越来越多的证据表明，这些环流单体的强度在十年时间尺度上发生了变化，可能在更大的尺度上产生重大的气候影响。瞬态示踪剂突出了新通风水进入海洋的路径。它们随时间演变的分布提供了对水团形成速率和循环以及地球化学过程速率的定量约束。氚是一种有价值的瞬态示踪剂，因为它具有独特的时间历程和边界条件，可以为其他示踪剂提供额外的信息。此外，它的子氦-3提供了额外的，独特的信息，因为它的互补（营养）的边界条件，所有其他瞬态示踪剂。将时间序列扩展到更长的时间提供了更长时间尺度的通气过程的描述和诊断短时间尺度过程中的时间变化的机会。此外，在氚分布和减少的时间导数中朝向更小的空间梯度的演变进一步最小化了氚/氦-3年龄中的非线性行为。通过重新占据重要的水文断面，观测这些示踪剂的演变分布将为海洋环流和通风的理论和模型提供强有力的约束。处理后的数据集将通过已建立的数据中心存档并公开提供。参与海洋环流、通风和气候变化建模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（例如，氯氟烃、放射性碳、氚/氦-3）已成为世界海洋环流实验（WOCE）和气候变化和可预测性计划（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影响到海洋，气候变化和应急响应计划自2003年以来一直在努力以大约十年的时间间隔重新占据WOCE的关键部分。该项目的主要目标是记录自WOCE占领以来24年来瞬态示踪剂氚和氦-3分布的时间演变，并利用这一信息诊断浅太平洋温跃层通风和对流翻转的变化率。此外，这些示踪剂的密度层，不直接露头在北太平洋的长期演变可能会提供有用的约束混合过程对通风的密度层的影响。研究人员将分析和解释2015年占领北太平洋中部P16 N部分获得的样本的氦同位素和氚测量结果，该部分跨越北方亚极地和亚热带环流以及北方和南方热带。