Placing the deep Baltic Sea sediment stratigraphy in a precise chronological framework: Improved paleoenvironmental studies and 14C reservoir age calibration

不断变化的气候和人类活动改变了波罗的海的生态系统，并在其沉积物的物理、生物和化学特性上留下了足迹。特别是来自深盆地的部分细层状沉积物，由于其亚年代际分辨率，是这些变化的宝贵档案。了解记录的环境变化背后的过程需要(i)了解它们的时间进展，即在一个事件中连续变化的确切时间和从事件到事件的时间跨度，以及（ii）将它们置于区域到半球的背景下。这些知识是针对波罗的海沉积物的，目前由于百年尺度的时间不确定性而受到阻碍。因此，利用波罗的海深海沉积物的近年代际环境信息，需要将它们放置在一个改进的时间框架中。宇宙起源放射性核素10Be和14C的全球共同产率变化可以为构建这样一个框架提供一个新的工具。一个覆盖中全新世的试验性10Be时间序列能够将西哥特兰盆地的波罗的海沉积物与IntCal20校准曲线上的绝对14C生产记录同步。这种排列将现有的百年年代学不确定性降低到±10-15年。在这个提议中，我们的目标是建立一个连续的十年尺度的10Be记录，来自西哥特兰盆地的沉积物，以及它与波罗的海整个咸淡咸水Littorina阶段（即过去8000年）的大气14C记录一致。此外，该项目将应用常见的宇宙生成放射性核素速率变化，使新的10Be记录与来自环波罗的海地区和整个北半球沉积物和冰芯档案的现有宇宙生成放射性核素时间序列同步。基于改进的时间限制，我们将确定波罗的海沉积物中与主要环境转变相关的物理、化学和生物代理响应的进展，并以亚年代际精度将其置于区域到半球背景下。这类调查为了解波罗的海生态系统对不同环境强迫的响应可能的时间范围和幅度提供了显著改进的约束条件，并使我们能够更好地预测人为气候变化的影响。此外，将基于10be的新年代学与现有14C年代学的系统偏移进行比较，可以构建14C储层年龄校准曲线，并将该档案中放射性碳定年的百年尺度不确定性降低到几十年。

Varying climate and human activity altered the Baltic Sea ecosystem and left their footprint in the physical, biological and chemical properties of its sediments. Particularly, the partly fine-laminated sediments from the deep basins are valuable archives of these changes, because of their sub-decadal resolution. Understanding the processes behind the recorded environmental changes requires (i) knowledge about their temporal progression, i.e. the exact timing of the succession of changes within an event and the time-span from event to event, and (ii) to put them in a regional to hemispheric context. This knowledge is for Baltic Sea sediments presently hampered due to centennial-scale chronological uncertainties. Therefore, utilizing the down to sub-decadal environmental information in deep Baltic Sea sediments necessitates their placement in an improved chronological framework. Globally common production rate variations of the cosmogenic radionuclides 10Be and 14C can provide a novel tool for constructing such a framework. A pilot 10Be time-series covering the Mid-Holocene enabled the synchronization of Baltic Sea sediments from the Western Gotland Basin to the absolute dated 14C production record from the IntCal20 calibration curve. This alignment reduced the existing centennial chronological uncertainties to ± 10-15 years. Within this proposal, we aim at the establishment of a continuous decadal-scale 10Be record from sediments of the Western Gotland Basin, as well as its alignment to the atmospheric 14C record for the complete brackish Littorina Stage of the Baltic Sea, i.e. the last 8000 years. In addition, the project will apply the common cosmogenic radionuclide production rate variations to synchronize the new 10Be record to existing cosmogenic radionuclide time-series from sediment and ice core archives in the Circum-Baltic region and across the Northern Hemisphere. Based on the improved chronological constraints, we will determine the progression of physical, chemical and biological proxy responses in Baltic Sea sediments associated with major environmental transitions at sub-decadal precision and place them into a regional to hemispheric context. Such investigations provide significantly improved constraints about possible temporal ranges and amplitudes of Baltic ecosystem responses to contrasting environmental forcing and allow us to better anticipate the effects of the anthropogenic climate change. In addition, comparing the new 10Be-based chronology with systematic offsets in existing 14C dates can enable us the construction of a 14C reservoir age calibration curve and reduce the presently centennial-scale uncertainties of radiocarbon dating in this archive to a few decades.