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

印度洋的边缘聚集了世界三分之一的人口，在20世纪世纪，印度洋的变暖速度比任何其他海洋盆地都快，并且与全球平均气温密切相关。这种稳定变暖的机制尚未完全了解，部分原因是不确定/稀疏的历史温度数据，但目前大气二氧化碳的上升显然起着重要作用。印度洋变暖影响到其周边国家的水文，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力事件，导致珊瑚漂白和大规模死亡。这些热应力事件是由印度洋-太平洋固有的逐年气候变化模式造成的。因此，必须重建受人为强迫影响时期之后的印度洋海表温度，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。大量生长的热带珊瑚，如滨珊瑚，形成年度生长带，并在其文石骨架中保存海洋表面温度（SST）和水文的地球化学指标。复制的热带印度洋多芯珊瑚年表可以提供延续几个世纪的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和珊瑚生长的影响。IndOC-W旨在分析来自桑给巴尔岛的大量长寿的大规模滨珊瑚，以建立热带印度洋的第一个多芯Sr/Ca-SST重建，该重建覆盖了300多年，并延伸到小冰期的最冷间隔。此外，我们将在选定的时间窗内测量珊瑚δ 18 O，以调查印度洋极端温度对赤道东非水文的影响。此外，这项研究将是第一个评估过去的热应力事件对微量元素的签名在滨珊瑚骨骼的影响，通过使用一种新的LA-ICP-OES/MS技术，将在基尔大学开发。在同伴项目（IndOC-E）中，T. Felis将利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流域尺度变暖和（II）相对于流域平均变暖率的空间变化。这对于评估印度洋变暖对印度洋沿岸国家水文的影响和验证气候模型结果至关重要。我们的项目为SPP 2299的整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模式之间的相互作用，以及它们对珊瑚礁生态系统和热带社会在变暖世界中的综合影响”。

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.”