Collaborative Research: Tracer Age-Based Estimates of Carbon Export and Ventilation Variability in the Indian Ocean

在过去的二十年里，印度洋的几个大型观测气候方案收集了一套全面的化学和物理海洋学数据。在这个项目中，所有可用的印度洋数据将结合起来，调查印度洋的碳循环和十年变化。该项目的时间安排是，拟议的工作将补充一个正在进行的由国家科学基金会资助的项目，该项目旨在通过水文观测确定三维印度洋环流。进行一项全面的全流域研究，以确定印度洋生物碳泵的强度，并调查沿沿着32°S的印度洋南部入口点的通风时间尺度的变化。建议的研究工作包括一个广泛的分析，来自通过时间分布（TTD）和相应的平均年龄分析的通风年龄。这一年龄信息将用于估计氧气利用率，脱氮和碳酸钙溶解的地下速率，以及支持这些速率所需的海洋表面有机和无机碳输出量。此外，在32°S，通风年龄的时间序列将构建基于该部分的四个职业。这将提供通风变化的时间尺度，可以在其他属性中看到，并可能与南方年度模式（SAM）。还将研究从三维印度洋环流估计推断出的纬向输送变化的相关性，数据分析将辅之以离线数值模拟，离线数值模拟采用包括示踪剂和基本海洋地球化学的等密度海洋环流模式。除了关于所用数据方法的敏感性研究外，还将开发离线代码的跟踪伴随。有了伴随项，就有可能确定在SAM的不同状态期间，32°S温跃层中沃茨的源区是否发生变化，以及远程强迫的变化如何影响在32°S观测到的示踪剂年龄变化。智力优势：从地下示踪剂数据推断表层海洋碳输出率是一种完全基于数据的“自下而上的方法”，可提供大规模的估计数。一种新的示踪剂，六氟化硫，将被用于一个双重示踪剂的方法与氯氟烃约束渡越时间分布和平均通风年龄。示踪剂伴随模式提供了一个工具，运行示踪剂“向后”跟踪异常回到他们的表面origin.Broader影响：拟议的工作将有助于分析数据的气候变率/碳重复水文计划和研究的十年气候变率。这项工作是跨学科的，涉及海洋物理学和海洋地球化学，将有助于全球碳循环的研究。由于印度洋全球海洋观测系统的发展，对印度洋的研究是及时的。所有三名调查员都参与了从高中到职业生涯早期指导妇女的各级教育的外联活动。一名研究生将参与拟议的工作，并接受海洋建模和瞬态示踪剂数据分析方面的培训。该项目是对美国CLIVAR（CLImate Variability and Predictability）计划的贡献。

Over the past two decades, several large observational climate programs in the Indian Ocean have collected a comprehensive chemical and physical oceanographic data set. In this project, all available Indian Ocean data will combined to investigate carbon cycling and decadal variability in the Indian Ocean. The timing of the project is such that the proposed work will supplement an ongoing NSF-funded project designed to determine the three-dimensional Indian Ocean circulation from hydrographic observations.This project has two main goals: To perform a comprehensive, basin-wide study to determine the strength of the biological carbon pump in the Indian Ocean, and to investigate changes in ventilation time scales at the southern entry point to the Indian Ocean along 32°S. The proposed research effort consists of an extensive analysis of ventilation ages derived from analysis of transit time distributions (TTDs) and the corresponding mean ages. This age information will be used to estimate subsurface rates of oxygen utilization, denitrification, and calcium carbonate dissolution, and the amount of organic and inorganic carbon export from the surface ocean needed to support these rates. In addition, at 32°S, a time series of ventilation ages will be constructed based on four occupations of this section. This will provide time scales for the ventilation variability that can be seen in other properties and that may be related to the Southern Annual Mode (SAM). Correlations with meridional transport variations inferred from the three-dimensional Indian Ocean circulation estimates will also be examined.The data analysis will be complemented by offline numerical simulations with an isopycnal ocean circulation model that includes tracers and basic biogeochemistry. In addition to sensitivity studies regarding the data methods used, a tracer adjoint for the offline code will be developed. With the adjoint, it will be possible to determine whether the source region of waters in the thermocline at 32°S changes during different states of the SAM and how changes in remote forcing may contribute to tracer age variability observed at 32°S. Intellectual Merit: Inferring surface ocean carbon export rates from subsurface tracer data is an entirely data-based, "bottom-up approach" that provides estimates on a large scale. A novel tracer, sulfur hexafluoride, will be used in a dual tracer approach with chlorofluorocarbons to constrain transit time distributions and mean ventilation ages. The tracer adjoint model provides a tool to run tracers "backwards" to trace anomalies back to their surface origin.Broader Impacts: The proposed work will contribute to the analyses of data from the CLIVAR/Carbon Repeat Hydrography Program and the study of decadal climate variability. The work is interdisciplinary, involving ocean physics and biogeochemistry, and will contribute to the study of the global carbon cycle. Studies of the Indian Ocean are timely because of the development of the Indian Ocean Global Ocean Observing System. All three investigators are involved in outreach activities at all educational levels from high school through mentoring women at the early states of their careers. A graduate student will be involved in the proposed work and receive training in ocean modeling and analyses of transient tracer data.This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) Program.