OCE-PRF: Steps Toward Quantitative ENSO Reconstruction: Modeling Ocean Circulation Near Coral Proxy Sites

概述：厄尔尼诺/南方涛动（ENSO）是太平洋气候变化的主要模式，其重建往往是从热带珊瑚的氧同位素比率（δ O-18）中创建的。这些记录为独立验证气候模型提供了重要信息，因为珊瑚三角洲O-18是现有的唯一高分辨率热带代用品之一。但由于所涉及的努力和费用，许多重建只使用少数珊瑚记录;然后解释三角洲O-18变化的ENSO行为，转换必须从当地的环境条件（如模型所示）和珊瑚礁上的同位素信号。在过去，这是通过对从网格化仪器数据得出的温度和盐度进行线性校准来实现的，但ENSO振幅的相关误差是巨大的;事实上，如此之大，以至于很难确定对模型物理学的具体改进。转换误差是由于一些组合：观测产品的不确定性，小规模的影响（涡流/混合）当地的珊瑚礁，或不明原因的大气影响。在这个项目中，该研究员将在一个现实的“完美模式”框架内，通过量化各种空间尺度上厄尔尼诺/南方涛动特性与δ O-18异常之间的关系，评估每一个过程的贡献。研究结果将改善未来的模型验证工作和现有珊瑚三角洲O-18记录的可解释性。智力优势：为这项研究开发的实验将嵌套一个区域海洋模型内的同位素启用，耦合大气环流模型（GCM）约束，以匹配20世纪的观测。这将提供一个空间上完整的三角洲O-18数据集的信息，在几个不同的网格尺度，这将作为一种功能的20世纪世纪？再分析？δ O-18;输出将作为公共资源提供给感兴趣的研究人员。区域范围将包括帕尔米拉环礁和基里蒂马蒂（圣诞岛）这两个赤道太平洋中部的珊瑚环礁，它们已被广泛用于古气候研究，对厄尔尼诺/南方涛动变化高度敏感，并受到热带和亚热带水团之间令人感兴趣的动态交换的影响。区域模拟将提供第一个全面的基于模型的热带太平洋环礁周围环流特征，此外还提供关于20世纪世纪厄尔尼诺/拉尼娜事件对珊瑚礁环境的海洋学影响的详细信息。帕尔米拉和基里巴斯也有大量的当地环境监测数据，这些数据将用于模型验证。 通过构造O-18三角洲的收支，将在全球和区域模式中诊断影响海水O-18三角洲的主要过程。这将确定，作为一个功能的空间尺度，哪些过程是最重要的三角洲O-18异常附近的网站用于代理收集。结果可以在未来的工作中使用，以验证GCM对代理数据：运行一个同位素启用的模型是必要的，如果是这样，在什么分辨率？三角洲O-18预算还将用于评估厄尔尼诺/拉尼娜事件的不同特性（即幅度、冷暖不对称性）如何被珊瑚化石记录下来，这最终可为改进大气环流模型中的物理参数化提供指导。更广泛的影响：该项目代表了一种全新的、高度跨学科的定量古气候重建方法，其结果将适用于各种各样的应用;所有模型输出都将公开提供。与NOAA太平洋岛屿渔业科学中心的合作将确保研究结果与生态应用相关，与太平洋海洋科学教育卓越中心（COSEE-Pacific）合作，与代表性不足的学生群体开展外联工作，将有助于提高公众对珊瑚礁保护的认识。夏威夷;主要赞助商），罗素布雷纳德（NOAA PIFSC），金科布（格鲁吉亚理工学院），马克梅里菲尔德（美国。夏威夷）、大卫努恩（CU-博尔德）

Overview: Reconstructions of the El Nino/Southern Oscillation (ENSO), the dominant mode of Pacific climate variability, are often created from the oxygen isotopic ratio (delta O-18) in tropical corals. These records provide crucial information for independent validation of climate models, as coral delta O-18 is one of the only high-resolution tropical proxies available. But because of the effort and expense involved, many reconstructions use only a handful of coral records; then to interpret delta O-18 variability in terms of ENSO behavior, a conversion must be made from local environmental conditions (as represented by the model) and the isotopic signal on the reef. In the past, this has been done using a linear calibration against temperature and salinity derived from gridded instrumental data, but the associated errors in ENSO amplitude are enormous; so large, in fact, that it becomes extremely difficult to identify specific improvements to model physics. The conversion errors are due to some combination of: uncertainties in observational products, small-scale effects (eddies/mixing) local to the reef, or unaccounted-for atmospheric influences. In this project, the fellow will assess the contribution of each of these processes, by quantifying the relationship between ENSO properties and delta O-18 anomalies on a variety of spatial scales in a realistic, "perfect-model" framework. The results will improve both future model validation efforts and the interpretability of existing coral delta O-18 records. Intellectual Merit: The experiments developed for this study will nest a regional ocean model within an isotope-enabled, coupled general circulation model (GCM) constrained to match 20th century observations. This will provide a spatially complete delta O-18 dataset with information on several different grid scales, which will function as a sort of 20th century ?reanalysis? of delta O-18; output will be provided as a public resource for interested researchers. The regional domain will cover both Palmyra Atoll and Kiritimati (Christmas) Island, two central equatorial Pacific coral atolls which have been used extensively for paleoclimate research, are highly sensitive to ENSO variability, and are influenced by dynamically interesting exchanges between tropical and subtropical water masses. The regional simulations will provide one of the first comprehensive model-based characterizations of circulation around tropical Pacific atolls, in addition to providing detailed information on the oceanographic impacts of 20th century El Nino/La Nina events on coral reef environments. Both Palmyra and Kiritimati also have extensive local environmental monitoring data available, which will be used for model validation. The dominant processes affecting seawater delta O-18 will be diagnosed in both the global and regional models, by constructing budgets of delta O-18. This will determine, as a function of spatial scale, which processes are most important for delta O-18 anomalies near sites used for proxy collection. The results can then be used during future efforts to validate GCMs against proxy data: is running an isotope-enabled model necessary, and if so at what resolution? The delta O-18 budgets will also be used to assess how different properties of El Nino/La Nina events (i.e. amplitude, warm/cold asymmetry) might be recorded by fossil corals, which can eventually provide guidance for improvements to physical parameterizations in GCMs. Broader Impacts: This project represents a fundamentally new and highly interdisciplinary approach to quantitative paleoclimate reconstruction, and the results will be useful for a wide variety of applications; all model output will be made publicly available. Collaboration with the NOAA Pacific Islands Fisheries Science Center will ensure that the results are relevant for ecological applications, and outreach work with underrepresented student populations around Oahu in collaboration with the Pacific Center for Ocean Science Education Excellence (COSEE-Pacific) will help to raise public awareness of coral reef conservation.Sponsoring Scientists: Brian Powell (U. Hawaii; lead sponsor), Russell Brainard (NOAA PIFSC), Kim Cobb (Georgia Tech), Mark Merrifield (U. Hawaii), David Noone (CU-Boulder)