GEN-EX – Metagenomics of Extreme-Wave Events

Extreme-wave events (tsunamis, storm surge and waves) pose significant hazards to coastal communities worldwide. Onshore deposits from these events significantly enhance our understanding of their long-term frequency-magnitude patterns, which are usually not covered by historical and instrumental documentation. Such perspectives are crucial for successful coastal hazard assessments and consequential efforts to mitigate against the loss of life and assets. Methods enabling reliable and consistent differentiation between the sedimentary evidence for tsunamis and storms remain elusive as deposits from both processes share a number of sedimentary criteria. Microfossil approaches (foraminifera, ostracods, diatoms) have yielded promising progress towards conclusive identification (PILARCZYK et al., 2014), however dissolution and bacterial degradation of carbonate tests often prevent microfossil identification. To address this issue in a pioneering project kicked-off in late 2017, we aim at using high-throughput, metagenomic sequencing techniques to identify marine organisms in onshore sand layers from their DNA remains and to unravel cryptic diversities. We focus on foraminifera, single-celled protists, which show depth-related zonation in subtidal environments and have already been traced successfully in palaeo-tsunami deposits by their ancient DNA (SZCZUCIŃSKI et al., 2016), and compare classic and molecular methods for their identification. Three objectives will be followed to reach this goal: 1. Quantify the relationship between water depth and the distribution of different species of foraminifera using both classic assemblage methods and metagenomic approaches. 2. Assess the potential for identifying key indicator species in extreme-wave deposits in different climate settings based on both assemblage approaches and metagenomic high-throughput sequencing techniques; 3. Establish how metagenomic approaches contribute to consistent and reliable differentiation between the sedimentary evidence for storms and tsunamis in coastal settings. The three key field areas, which share an abundance of published, well-dated evidence for both storms and tsunamis, comprise the Shetland Islands, south central Japan, and southern Chile. The Shetland Islands have a temperate oceanic climate, and near-shore lakes and coastal peat lowlands feature sand sheets deposited by the submarine Storegga landslide around 8 ka years ago and a younger tsunami dated to 1.5 ka (e.g. BONDEVIK et al., 2005). Extreme-wave deposits from south central Japan, underlying a subtropical climate, are available through the ongoing BELSPO BRAIN-be-funded QuakeRecNankai project, focusing on records of past earthquakes and tsunamis along the Nankai Trough (GARRETT et al., 2016). At temperate-humid Chaihuin, southern Chile, deposits of the 1960 Chile tsunami and several older events have been documented (HOCKING & GARRETT, 2016) and sampled for identification of foraminiferal assemblages based on DNA remains. REFERENCES BONDEVIK, S., MANGERUD, J., DAWSON, S., DAWSON, A. & LOHNE, Ø. 2005. Evidence for three North Sea tsunamis at the Shetland Islands between 8000 and 1500 years ago. — Quaternary Science Reviews, 24: 1757–1775. GARRETT, E., FUJIWARA, O., GARRETT, P., HEYVAERT, V.M.A., SHISHIKURA, M., YOKOYAMA, Y., HUBERT-FERRARI, A., BRÜCKNER, H., NAKAMURA, A., DE BATIST, M. & THE QUAKERECNANKAI TEAM. 2016. A systematic review of geological evidence for Holocene earthquakes and tsunamis along the Nankai-Suruga Trough, Japan. — Earth-Science Reviews, 159: 337–357. HOCKING, E. & GARRETT, E. 2016. Geological records of recent and historical ruptures of the Chilean subduction zone: a latitudinal transect of earthquake deformation and tsunami inundation. — Geophysical Research Abstracts, 18: EGU2016-938. PILARCZYK, J.E., DURA, T., HORTON, B.P., ENGELHART, S.E., KEMP, A.C. & SAWAI, Y. 2016. Microfossils from coastal environments as indicators of paleo-earthquakes, tsunamis and storms. — Palaeogeography, Palaeoclimatology, Palaeoecology, 413: 144–157. SZCZUCIŃSKI, W., PAWŁOWSKA, J., LEJZEROWICZ, F., NISHIMURA, Y., KOKOCIŃSKI, M., MAJEWSKI, W., NAKAMURA, Y. & PAWLOWSKI, J. 2016. Ancient sedimentary DNA reveals past tsunami deposits. — Marine Geology, 381: 29–33.

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