Uncharted offshore archives – organic geochemical imprints on the Algarve shelf

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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.