Indian Ocean warming from the peak of the Little Ice Age to the 21st century: Zanzibar Island, Western Indian Ocean (IndOC-W)

印度洋聚集了世界三分之一的人口，在20世纪，印度洋变暖的速度比其他任何洋盆都快，而且与全球平均气温有很强的联系。这种稳定变暖背后的机制尚未被完全理解，部分原因是历史温度数据不确定/稀少，但目前大气中二氧化碳的上升显然起到了重要作用。印度洋变暖影响了其周边国家的水文，并威胁到珊瑚礁生态系统，这些生态系统经历了反复的热应激事件，导致珊瑚漂白和大规模死亡。这些热应激事件是由印度-太平洋固有的气候变化的年际模式引起的。因此，至关重要的是重建受人为强迫影响的时期以外的印度洋海洋表面温度，以确定印度洋变暖的开始及其与工业化前全球表面温度的关系。像Porite这样的大规模生长的热带珊瑚形成了年生长带，并在它们的文石骨架中保存了海洋表面温度(SST)和水文学的地球化学指标。来自热带印度洋的复制的多核心珊瑚年表可以提供跨越几个世纪的SST重建(包括不确定性)，并可用于评估历史温度趋势、人为变暖的开始及其对水文学和珊瑚生长的影响。INDOC-W的目标是分析来自桑给巴尔岛的大量长期存活的巨大波利特珊瑚，以建立第一个覆盖300多年并延伸到小冰期最冷时期的热带印度洋多核锶/钙-海温重建。此外，我们将在选定的时间窗口测量珊瑚δ18O，以调查印度洋极端温度对赤道东非水文的影响。此外，这项研究将首次使用基尔大学将开发的一种新的LA-ICPOES/MS技术来评估过去的热应力事件对Porites骨骼中微量元素特征的影响。在一个配套项目(INDOC-E)中，T.Felis将使用安达曼海的珊瑚重建东印度洋的温度和水文。INDOC-W和INDOC-E的结果使我们能够估计(I)从小冰期到现在的印度洋盆地尺度的升温，以及(Ii)升温速率相对于盆地平均值的空间变化。这对于评估印度洋变暖对印度洋沿岸国家水文学的影响以及验证气候模型结果至关重要。我们的项目对SPP 2299的总体科学使命做出了重大贡献，即“了解全球气候变化和热带气候变异性模式之间的相互作用，以及它们对变暖世界中的珊瑚礁生态系统和热带社会的综合影响。”

The Indian Ocean, which gathers one-third of the world’s population around its rim, has been warming faster than any other ocean basin during the 20th century and is strongly coupled to global mean temperatures. The mechanisms underlying this steady warming are not fully understood, in part due to uncertain/sparse historical temperature data, but the current rise in atmospheric CO2 clearly plays an important role. Indian Ocean warming affects the hydrology in the countries around its rim and threatens coral reef ecosystems, which experienced repeated thermal stress events that caused coral bleaching and mass mortality. These thermal stress events are caused by year-to-year modes of climate variability inherent in the Indo-Pacific. It is therefore vital to reconstruct Indian Ocean sea surface temperatures beyond the period influenced by anthropogenic forcing, in order to determine the onset of Indian Ocean warming and its relationship with global surface temperatures in the pre-industrial. Massive-growing tropical corals such as Porites form annual growth bands and preserve geochemical proxies of sea surface temperature (SST) and hydrology in their aragonite skeletons. Replicated, multi-core coral chronologies from the tropical Indian Ocean can provide SST reconstructions (including uncertainties) that extend over several centuries and can be used to evaluate historical temperature trends, the onset of anthropogenic warming and its impact on hydrology and coral growth. IndOC-W aims to analyse a large set of long-lived massive Porites corals from Zanzibar Island to establish the first multi-core Sr/Ca-SST reconstruction from the tropical Indian Ocean that covers more than 300 years and extends into the coldest interval of the Little Ice Age. In addition, we will measure coral δ18O in selected time windows to investigate the impact of extreme temperatures in the Indian Ocean on hydrology in equatorial East Africa. In addition, this study will be the first to assess the impact of past thermal stress events on trace element signatures in Porites skeletons by using a new LA-ICP-OES/MS technique that will be developed at Kiel University. In a companion project (IndOC-E), T. Felis will reconstruct eastern Indian Ocean temperature and hydrology using corals from the Andaman Sea. Results of IndOC-W and IndOC-E allow us to estimate (I) the basin-scale warming of the Indian Ocean from the Little Ice Age to the present and (II) spatial variations in warming rates relative to the basin mean. This is crucial to assess the impact of Indian Ocean warming on hydrology in the countries bordering the Indian Ocean and to validate climate model results. Our project significantly contributes to the overall scientific mission of the SPP 2299, namely to “understand the interaction between global climate change and modes of tropical climate variability, and their combined impact on coral reef ecosystems and tropical societies in a warming world.”