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

合作研究：基于示踪剂年龄的印度洋碳输出和通风变化估计

• 批准号: 1059881
• 负责人: Alison Macdonald
• 金额: $ 6.83万
• 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: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2016-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1059881&HistoricalAwards=false
• 关键词: Collaborative; Research; Tracer; Age; Based

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.

在过去的二十年里，印度洋的几个大型气候观测项目收集了一套全面的化学和物理海洋学数据集。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年代际变化。该项目的时间安排是这样的，拟议的工作将补充正在进行的美国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。该项目有两个主要目标：进行一项全面的、全流域的研究，以确定印度洋生物碳泵的强度，并调查沿32°S向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通过分析传输时间分布（TTDs）和相应的平均年龄对通风年龄进行广泛的分析。这些年龄信息将用于估计氧气利用、反硝化和碳酸钙溶解的地下速率，以及支持这些速率所需的从海洋表面输出的有机和无机碳的数量。此外，在32°S处，将根据该部分的四个职业构建通风年龄的时间序列。这将提供通风变化的时间尺度，可以在其他属性中看到，这可能与南方年模态（SAM）有关。还将研究从三维印度洋环流估计推断出的经向输送变化的相关性。数据分析将辅以离线数值模拟，采用包括示踪剂和基本生物地球化学在内的等环流海洋环流模式。除了对所使用的数据方法进行敏感性研究外，还将开发脱机代码的示踪伴随物。有了伴随物，就有可能确定32°S温跃层的水源区是否在SAM的不同状态期间发生变化，以及远程强迫的变化如何有助于在32°S观测到的示踪剂年龄变率。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”，它提供了大规模的估计。一种新型示踪剂六氟化硫将与氟氯化碳一起用于双示踪剂方法，以限制传输时间分布和平均通风年龄。示踪剂伴随模型提供了一种工具，可以“反向”运行示踪剂，将异常追溯到其地表起源。更广泛的影响：拟议的工作将有助于CLIVAR/碳重复水文计划的数据分析和年代际气候变率的研究。这项工作是跨学科的，涉及海洋物理学和生物地球化学，并将有助于研究全球碳循环。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。所有三名调查人员都参与了从高中到指导处于职业生涯早期阶段的妇女的所有教育水平的推广活动。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数据分析方面的培训。该项目是对美国CLIVAR（气候变率和可预测性）计划的贡献。