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

在过去20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。在这个项目中，所有可用的印度洋数据将结合在一起，以调查印度洋的碳循环和年代际变化。该项目的时间安排是对NSF资助的一个正在进行的项目的补充，该项目旨在从水文观测中确定印度洋的三维环流。该项目有两个主要目标：进行一项全面的、全盆地范围的研究，以确定印度洋生物碳泵的强度，并调查沿32°S的印度洋南部入口点的通风时间尺度的变化。拟议的研究工作包括对通过时间分布(TDS)和相应的平均年龄的分析得出的通风年龄的广泛分析。这些年龄信息将被用来估计氧利用、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表层海洋输出的有机和无机碳的数量。此外，在32°S，将根据该区段的四种职业构建通风年龄时间序列。这将提供通风可变性的时间标尺，可以在其他物业中看到，并且可能与南方年度模式(SAM)有关。还将审查从三维印度洋环流估计中推断的经向输送变化的相关性。数据分析将得到包括示踪剂和基本生物地球化学的等周期海洋环流模式的离线数值模拟补充。除了对所使用的数据方法进行敏感性研究外，还将为离线代码开发一个伴随的示踪剂。有了伴随项，就有可能确定32°S温跃层中水的源区在水层管理不同状态期间是否发生变化，以及远程强迫的变化可能如何有助于在32°S观察到的示踪剂年龄变异性。一种新的示踪剂，六氟化硫，将用于与氯氟烃的双重示踪剂方法，以限制通过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，使示踪剂“倒退”，以追溯异常的地表来源。广泛影响：拟议的工作将有助于分析CLIVAR/碳重复水文计划的数据和研究十年气候变异性。这项工作是跨学科的，涉及海洋物理和生物地球化学，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。这三名调查人员都参与了从高中到在女性职业生涯早期指导她们的所有教育水平的外联活动。一名研究生将参与这项拟议的工作，并接受海洋建模和瞬时示踪剂数据分析方面的培训。该项目是对美国CLIVAR(气候可变性和可预测性)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.