Uncharted offshore archives – organic geochemical imprints on the Algarve shelf

地球广阔的近海地区及其全新世的沉积记录在很大程度上是一个未知的领域。特别是对于古环境和极端波浪事件的研究，对未接触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。先前和初步的近海研究结果表明，在海洋环境中，超过连续河流背景的陆地反冲物质的识别和环境影响具有明显的事件特征。因此，我们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的定量和定性动员，在近海系统中产生单一的叠加事件沉积；(2)近海沉积档案是追踪海啸反冲叠加陆流的有利环境。在RV METEOR巡航M152期间，收集了大量来自阿尔加维大陆架的沉积物岩心样本，以研究阿尔加维大陆架的古环境演化，并区分和表征公元1755年里斯本海啸和其他短期高能事件的对比不连续层。为了实现这一目标，该项目采用综合有机地球化学方法调查获得的近海样品，并辅以互补的沉积学和微古生物学数据。项目工作包包括：(a)确定完整的有机地球化学化合物光谱，选择适当的环境敏感型有机地球化学指标，反映和区分长期和短期的环境变化；(b)阿尔加维陆架环境演化的地球化学重建和影响陆架的长期过程与短期事件的区分；(c)识别公元1755年里斯本海啸和具有确定的有机标志的潜在前事件沉积物；(d)近海地球化学特征与陆地地球化学特征的比较；最后(e)通过有机地球化学的见解确定事件矿床的空间分布和反冲机制的检验。在实现这些项目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，以重新评估欧洲大西洋海岸线的海啸危害，而且还了解海啸反冲的水动力过程的基本知识。这样，未来的海啸研究将从一个真实的近海数据集中获得巨大收益，以便为地方当局改进灾害和减灾管理制作海啸灾害地图和情景。

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.