Developing a 3.5-million-year benchmark record of Indian Ocean Dipole variability

开发印度洋偶极子变率 350 万年的基准记录

• 批准号: 447653483
• 负责人: Professorin Dr. Stefanie Kaboth-Bahr
• 金额: --
• 依托单位: Institut für Geologische Wissenschaften
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/447653483?language=en
• 关键词: Developing; 3.5; million; year; benchmark

The Indian Ocean Dipole (IOD) is the leading mode of interannual variability of sea surface temperature (SST) in the tropical Indian Ocean. The IOD describes warm (positive) and cold (negative) sea surface temperatures oscillations in the western and eastern part of the Indian ocean. The societal most relevant consequences of IOD variability range from extreme floods in eastern Africa to severe droughts in Australia. These extreme climate events caused by the IOD are predicted to become more common in the future as greenhouse gas emissions increase. Yet despite these alarming predictions and its profound impact on the bordering regions which sustain more than 2 billion people, surprisingly little is known about IOD variability in the past. In particular, the proposed sensitivity of the IOD to CO2 could be further tested if IOD variability during geological time intervals of higher CO2 contents were known. However, the insights into past IOD variability have been severely hampered by the lack of appropriate sedimentary and geochemical data sets from Indian Ocean.The here proposed research aims to elucidate IOD changes during the last 3.5 million years which coincides with distinct changes in the global CO2 level; including the mid-Pliocene warm period considered an analogue for future climate change. At the heart of this project stands the hypothesis that IOD-related SST and the associated surface wind anomalies influenced the Ekman transport of the deep meridional overturning circulation in the Indian Ocean, and thus the ventilation of the deep-water regime. Based on observational data, the weakening (strengthening) of the Ekman transport during positive (negative) IOD phases facilitates less (more) ventilation of the deep-water regime, and consequently a shoaling (deepening) of the lysocline. These new modern hydrographic findings have not yet been applied to the geological past, and thus open up an entire new avenue to research past IOP changes. Hence, this project aims to ground truth the possibility of utilizing deep-water ventilation changes in the western Indian Ocean throughout the geological past as an index of IOD variability. Two hypotheses will be specifically tackled in this project:1) Carbonate dissolution cycles as an indicator of deep-water ventilation changes in the western Indian Ocean can be used as IOD intensity index,2) The amplitude of the IOD is linear correlated to changes in global CO2 levels.To decipher its past deep-water ventilation variability in unprecedented temporal resolution, a sediment core from Site ODP 709 situated in the western equatorial Indian Ocean - a key region of IOD forcing – will be investigated utilizing a novel IOD proxy based on XRF core scanning, stable-isotope and Mg/Ca-paleothermometry based on benthic and planktic foraminifera. The synthesis of the collected data will then be used to develop a new benchmark record of IOD variability during the last 3.5 million years.

印度洋偶极子（IOD）是热带印度洋海表温度（SST）年际变化的主要模态。IOD描述了印度洋西部和东部的暖（正）和冷（负）海面温度振荡。IOD变异性的社会最相关的后果包括从东非的极端洪水到澳大利亚的严重干旱。随着温室气体排放量的增加，这些由IOD引起的极端气候事件预计将在未来变得更加普遍。然而，尽管有这些令人震惊的预测及其对维持20多亿人口的边境地区的深远影响，但令人惊讶的是，过去对IOD的变化知之甚少。特别是，如果已知IOD在CO2含量较高的地质时间间隔内的变化，则可以进一步测试IOD对CO2的拟议敏感性。然而，过去IOD的变化的见解已严重阻碍了缺乏适当的沉积和地球化学数据集从IndianOcean.这里提出的研究旨在阐明IOD的变化在过去的350万年，正好与全球CO2水平的明显变化，包括上新世中期温暖期被认为是未来气候变化的模拟。该项目的核心假设是，与IOD相关的SST和相关的表面风异常影响了印度洋深层纬向翻转环流的Ekman输送，从而影响了深水区的通风。根据观测数据，减弱（加强）的Ekman运输过程中的积极（消极）IOD阶段有利于更少（更多）通风的深水区，因此变浅（加深）的溶跃层。这些新的现代水文学发现尚未应用于过去的地质，因此开辟了一个全新的途径来研究过去的IOP变化。因此，该项目旨在将西印度洋整个地质历史的深水通风变化作为IOD变化指数的可能性。该项目将具体解决两个假设：1）碳酸盐溶解循环作为印度洋西部深水通气变化的指标，可用作IOD强度指数，2）IOD的幅度与全球CO2水平的变化呈线性相关，为了以前所未有的时间分辨率解释其过去的深水通气变化，将利用基于XRF岩心扫描，稳定同位素和基于底栖和南极有孔虫的Mg/Ca古温度测量的新型IOD代用品对位于赤道印度洋西部的ODP 709站点的沉积物岩心进行研究。然后，将利用收集到的数据的综合结果，建立过去350万年IOD变化的新基准记录。