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Tropical Indian Ocean and East African seasonality during the Holocene: orbital forcing and ocean atmosphere interactions. (IndoOrb)

全新世热带印度洋和东非季节性：轨道强迫和海洋大气相互作用。

基本信息

批准号：
260218773
负责人：
Professorin Dr. Miriam Pfeiffer
金额：
--
依托单位：
Arbeitsgruppe Paläontologie - Historische Geologie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/260218773?language=en
关键词：
Tropical Indian Ocean East African

项目摘要

East African rainfall has declined significantly over recent decades, culminating in the extreme drought of 2010-2011 at the Horn of Africa. Instrumental and proxy data suggest that the tropical Indian Ocean has a primary influence on the long-term drying trend of East Africa. Of particular importance for East African rainfall is the warming of the so-called Seychelles-Chagos thermocline ridge (SCTR) located in the south-central Indian Ocean. The SCTR features a shallow thermocline and high mean sea surface temperatures (>28°C), allowing strong ocean-atmosphere interactions on various time scales. This project investigates (I) intraseasonal and interannual ocean-atmosphere interactions in the SCTR region, (II) their response to changes in orbital parameters during the Holocene and (III) their impact on rainfall variability in East Africa. As the instrumental data is very limited in time, I will use geochemical proxy data from modern and fossil corals to address these problems. I have chosen the following approach: (I) the corals will be sampled at weekly to bi-weekly resolution. This is necessary to capture intraseasonal events. (II) In the SCTR region, proxies that capture surface ocean parameters (Sr/Ca and stable oxygen isotopes: sea-surface-temperature and salinity) are coupled with proxies that record the nutrient content of surface waters (stable nitrogen isotopes). The latter is related to upwelling and thermocline variability. (III) Corals from East Africa are used to reconstruct river runoff using Ba/Ca and skeletal luminescence. The project focuses on orbital time scales. During the Holocene, changes in orbital parameters led to changes in seasonality that are comparable to interannual anomalies of the seasonal cycle observed today. For example, in the SCTR region positive Indian Ocean Dipole events cause a warming in September-November. Model data suggest that this is coupled with a deepening of the thermocline and reduced upwelling of nutrient-rich waters. In East Africa, rainfall is above average. During the mid-Holocene (6kyr BP), insolation in the SCTR region peaks in September-November (6 kyr BP). How does this affect upwelling in the SCTR region, and what is the rainfall response in East Africa? The processes observed on orbital time scales may allow a better understanding of the dynamical relationship between ocean-atmosphere interactions and external forcing in the Indian Ocean sector. This should provide important constraints on the response of the Indian Ocean to global warming.

近几十年来，东非降雨量大幅减少，最终导致非洲之角 2010 年至 2011 年出现极端干旱。仪器和代理数据表明，热带印度洋对东非的长期干燥趋势具有主要影响。对东非降雨特别重要的是位于印度洋中南部的塞舌尔-查戈斯温跃层脊（SCTR）的变暖。 SCTR 具有浅温跃层和高平均海面温度 (>28°C)，允许在不同时间尺度上发生强烈的海洋-大气相互作用。该项目研究 (I) SCTR 区域的季节内和年际海洋-大气相互作用，(II) 它们对全新世期间轨道参数变化的响应，以及 (III) 它们对东非降雨量变化的影响。由于仪器数据的时间非常有限，我将使用来自现代珊瑚和化石珊瑚的地球化学代理数据来解决这些问题。我选择了以下方法：（I）将以每周到每两周的分辨率对珊瑚进行采样。这对于捕获季节内事件是必要的。 (II) 在 SCTR 区域，捕获表面海洋参数（Sr/Ca 和稳定氧同位素：海面温度和盐度）的代理与记录地表水营养物含量（稳定氮同位素）的代理相结合。后者与上升流和温跃层变化有关。 (III) 来自东非的珊瑚被用来利用 Ba/Ca 和骨骼发光来重建河流径流。该项目的重点是轨道时间尺度。在全新世期间，轨道参数的变化导致季节性变化，与今天观察到的季节周期的年际异常相当。例如，在 SCTR 地区，积极的印度洋偶极子事件导致 9 月至 11 月变暖。模型数据表明，这与温跃层的加深和营养丰富的水域的上升流减少有关。在东非，降雨量高于平均水平。在全新世中期（距今 6 公里），SCTR 地区的日照在 9 月至 11 月（距今 6 公里）达到峰值。这对 SCTR 地区的上升流有何影响？东非的降雨反应如何？在轨道时间尺度上观测到的过程可能有助于更好地了解印度洋区域海洋-大气相互作用与外强迫之间的动态关系。这应该对印度洋对全球变暖的反应提供重要的限制。