Uncharted offshore archives – organic geochemical imprints on the Algarve shelf

地球上广阔的近海地区及其全新世沉积记录是一个很大程度上未知的领域。特别是对于古环境和极端波浪事件的研究，对未触及的和长期的近海档案的调查可能是有利的，但在科学上代表性不足。先前和初步海上结果表明，超过海洋环境中连续河流背景的反冲洗陆地物质的识别和环境影响呈现出不同的事件特征。据此，本文提出了以下工作假设：（1）海啸引起陆地物质和相关有机质的单一和高能量的定量和定性活动，在近海系统中产生单一叠加事件沉积;（2）近海沉积档案是追踪海啸的有利环境，在RV METEOR巡航M152期间，从阿尔加维大陆架收集了大量沉积物岩心样品，其前提是研究阿尔加维大陆架的古环境演变，并区分和描述对比AD 1755年里斯本海啸和其他之前的短期高能事件的不连续层。为实现这一目标，该项目以沉积学和微体古生物学补充数据为支持，采用全面的有机地球化学方法调查所获得的近海样品，项目的一揽子工作包括：（a）查明全部有机地球化学化合物谱，选择适当的环境敏感有机地球化学代用指标，这些代用指标反映并能够区分长期和短期的环境变化;（B）阿尔加维大陆架环境演变的地球化学重建和影响大陆架的长期过程和短期事件之间的区别;（c）用确定的有机标志物确定AD 1755年里斯本海啸和潜在的前事件存款;（d）将获得的近海地球化学特征与陆地对应物进行比较;在实现这些项目的目标和收集新信息的过程中，我们的目标不仅是遇到新的发现来重新评估欧洲大西洋海岸线的海啸危险，而且还要了解海啸发生的水动力过程的基本原理。这样，未来的海啸研究将大大受益于一个真实的海上数据集，以产生海啸灾害地图和情景，改善灾害和减灾管理，从地方当局。

The earth’s vast offshore areas and their Holocene sedimentary records are a largely uncharted domain. For paleoenvironmental and extreme wave events research in particular, the investigation of untouched and long-term offshore archives might be of favor but is underrepresented in science. Prior and preliminary offshore results indicate that the identification and environmental impact of backwashed terrestrial material exceeding the continuous fluvial background in marine settings, presents distinct events signatures. Accordingly, the following working hypotheses are derived: (1) Tsunamis cause a singular and a highly energetic quantitative and qualitative mobilization of terrestrial material and associated organic matter, generating singular superimposed event deposits in offshore systems; (2) Offshore depositional archives represent favorable environments for tracing the tsunami backwash-driven superimposed terrestrial discharge.During the RV METEOR cruise M152 an extensive sample set of sediment cores from the Algarve shelf was collected with the premise to examine the paleoenvironmental evolution of the Algarve shelf and differentiate and characterize contrasting discontinuous layers of the AD 1755 Lisbon tsunami and other preceding short-term high-energy events. To achieve this, the project investigates the obtained offshore samples with a comprehensive organic geochemical approach supported by complementary sedimentological and micropaleontological data.The projects work packages include (a) the identification of the full organic geochemical compound spectrum and the selection of suitable environment-sensitive organic geochemical proxies that reflect and can differentiate long-term but also short-term environmental changes; (b) the geochemical reconstruction of the environmental evolution on the Algarve shelf and differentiation between long-term processes and short-term events affecting the shelf; (c) the identification of the AD 1755 Lisbon tsunami and potential preceding event deposit with the defined organic markers; (d) the comparison between gained offshore geochemical characteristics with their terrestrial counterparts; and lastly (e) the determination of the spatial distribution of event deposits and examination of backwash mechanisms through organic-geochemical insights.In achieving these project’s goals and gathering new information we aim to not only encounter novel discoveries to reassess the tsunami hazard for the European Atlantic coastline but also understand fundamental basics of hydrodynamic processes of tsunami backwash. By this, future tsunami research will profit substantially from an authentic offshore dataset in order to produce tsunami hazard maps and scenarios for an improved hazard and mitigation management from local authorities.