Micrometer-scale biomarker and elemental imaging on sediments from the northeastern Arabian Sea – reconstruction of the Indian monsoon evolution on a sub-decadal scale in the Holocene and the Bølling-Allerød interstadial

印度季风是低纬地区最重要的大尺度陆海气耦合现象之一。然而，十年尺度季风变化的强迫机制还不是很清楚，因为关于短期气候振荡的知识大多局限于仪器记录所覆盖的周期。由于保存未受干扰的信号的记录数量较少，以及获取高分辨率记录的方法限制，对较遥远过去的短期气候演变的理解受到阻碍。然而，最近用新的成像技术审问层状沉积物的发展显示出克服这些限制的巨大潜力。为了揭示热带地区亚十年尺度的古气候演化，我建议将生物标志物和元素成像应用于横跨全新世大部(11.7-2ka)和Bölling-Alerød间期(B-A；14.7-12.9ka)的阿拉伯海细层沉积剖面。该项目的目标是探索全新世和B-A期间热带辐合带(ITCZ)、印度季风强度和相关环境响应在亚十年和十年尺度上的相互作用。来自阿拉伯海的沉积岩芯SO130-289KL保存了拟议时间间隔的未受干扰的分层记录，为高分辨率研究提供了良好的档案。我建议应用质谱学成像技术，这是古气候研究中的一种新技术，它收集有机化合物的质谱图并显示其在微米尺度上的空间分布，并将其与全新世和B-A间期沉积的沉积物中的一致微X射线荧光数据相结合。其目的是将海洋表面温度(SST)的独立生物标志物指标与200微米(即年度)分辨率的陆地植被响应、水生初级生产力和水柱缺氧的指标结合起来，并将这些数据与在50微米分辨率下获得的指示环境条件的元素比率联系起来。获得每年可分辨的生物标志物和元素记录将揭示以前无法获取的关于间冰期和间歇性气候状态下季风强度及其与ITCZ的关系的信息，并通过以前所未有的详细程度探测海洋、大气和陆地对气候变化的反应中的领先和滞后，精确地确定季风对环境的强迫。在过去~15ka的温暖气候状态中建立气候变率优势频率的保守方法将被用来检验准持续年代际振荡的存在。该项目还将限制全新世和B-A期间热带地区SST的变化速度及其变异性。总之，该项目将提供高分辨率的生物标志物和元素数据，可作为全新世和B-A期热带亚年代际气候演变的参考记录。

The Indian monsoon is one of the most important large-scale coupled land-ocean-atmosphere phenomena in the low latitudes. However, the forcing mechanisms of the decadal-scale monsoon variability are not well understood because knowledge of short-term climate oscillations is mostly limited to periods covered by instrumental records. Understanding of the short-scale climate evolution in the more distant past is hampered by the small number of records that preserve undisturbed signals and by methodological limitations to obtain highly resolved records. However, recent developments that interrogate laminated sediments with novel imaging techniques showed great potential to overcome these limitations. In order to reveal subdecadal-scale paleoclimate evolution of the tropics, I propose to apply biomarker and elemental imaging on finely laminated sediment sections from the Arabian Sea spanning the major part of Holocene (from 11.7-2 ka) and Bølling-Allerød interstadial (B-A; 14.7-12.9 ka). The goal of this project is to explore the interplay of the Intertropical Convergence Zone (ITCZ), Indian monsoon intensity and related environmental responses on the subdecadal and decadal-scale during the Holocene and B-A.Sediment core SO130-289KL from the Arabian Sea preserves an undisturbed, laminated record for proposed time intervals, providing an excellent archive for high-resolution studies. I propose to apply mass spectrometry imaging, a novel technique in paleoclimate research that collects mass spectra of organic compounds and visualizes their spatial distribution at the µm-scale, and combine it with congruent µXRF data from sediments deposited during the Holocene and B-A interstadial. The aim is to combine independent biomarker proxies for sea-surface temperature (SST) with proxies of terrestrial vegetation response, aquatic primary productivity and water column anoxia in 200 µm (i.e. annual) resolution and relate this data to elemental ratios indicative of environmental conditions acquired at 50 µm resolution. Obtained annually resolved biomarker and elemental records will reveal previously inaccessible information on monsoon intensity and its relation to ITCZ in interglacial and interstadial climate states, as well as precisely establish monsoon forcing on the environment by detecting leads and lags in the responses of the ocean, atmosphere and land to climate change in an unprecedented level of details. A conservative approach in establishing dominant frequencies of climate variability in warm climate states of the past ~15 ka will be applied to test for the existence of quasi-persistent decadal oscillations. This project will also constrain the rate of SST change and its variability in the tropics over the Holocene and B-A. In summary, this project will provide highly-resolved biomarker and elemental data that could serve as a reference record for subdecadal climate evolution in the tropics during the Holocene and the B-A.