Using foraminifera to reconstruct past bathymetry and geohazard events offshore Taiwan


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Due to its unique location, Taiwan is prone to extreme events linked to climate (e.g., typhoons) and tectonics (e.g., earthquakes). These extreme events can trigger submarine landslides in the form of turbidity currents.In the sedimentary records offshore Taiwan, many turbidite layers can be identified, but little is known about the provenance of sediments (original water depth) or the triggers (i.e., typhoons vs. earthquakes).

In order to expand the toolbox to study submarine landslides offshore Taiwan, graduate students (Edwin Sicheng Le and Jheng-Kuan Lin) and researchers (Raul Tapia, Sze Ling Ho, and Chih-Chieh Su) from IONTU assessed the usefulness of planktic and benthic foraminifera to identify submarine landslides and estimate the original water depth of the material transported downslope.

The study used 148 samples of surface sediments collected offshore Taiwan in the past 20 years on board of Taiwanese research vessels, including NOR1, OR1, OR2, and OR3. In addition, the study also used samples collected during a Taiwan-France cruise in 2018 on board of R/V Marion Dufresne. Using these sediments, foraminifera abundance, grain size distribution, TOC, and C/N data were generated. These data are then compared to hydrographic data collected and curated by Ocean Data Bank and GLODAP database.

The results show that offshore Taiwan foraminiferal abundance and planktic-benthic foraminifera ratio (%P) correlate strongly with water depth. %P increases (decreases) as the water depth increases (decreases). Therefore, using this water depth-%P equation, sediments influenced by submarine landslides can be identified, as the %P values of these sediments would be very different from sediments in the same water depth range. These data are merged with datasets collected from other regions to generate a global water depth-%P equation. This equation can be used on sediment records to reconstruct paleobathymetry and paleo extreme events triggered by earthquakes or typhoons.

The research was published in Marine Geology and titled “Planktic-benthic foraminifera ratio (%P) as a tool for the reconstruction of paleobathymetry and geohazard: A case study from Taiwan”.


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