Urlaub, Morelia , Belo, Julie, Berndt, Christian , Klein, Elisa , Wollschläger, Jochen and Völsch, Anne (2023) Reconstructing volcanic eruptions and tsunamis of Krakatau Volcano - Transit, Cruise No. SO299/2, 15.08.2023 – 02.09.2023, Singapore (Singapore) – Port Louis (Mauritius) REE_T BIO-OPS_2023. . SONNE-Berichte, SO299/2 . Begutachterpanel Forschungsschiffe, Bonn, 36 pp. DOI 10.48433/cr_so299_2.

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Abstract

Cruise SO299/2 of the German Research Vessel SONNE was a transit cruise with four working
days. The main scientific focus was on Krakatau archipelago in the Sunda Strait, source of at least
two major tsunamis in historic times. Reflection seismic profiles, hydroacoustic data, and sediment
cores were collected west, south, and east of the archipelago. Furthermore, bio-optical
observations for an improved underwater light field characterization and parametrization within
the Indian Ocean were conducted on a transect from Singapore to Mauritius. Seismic imaging
reveals three seismically different types of deposits, possibly originating from the 1883 events
given their proximity to the modern seafloor. One of the deposits is topped by large blocks with
diameters up to 400 m that stick out up to 30 m from the surrounding seafloor. Normal faults
spread around the surveyed area show recent activity up until the presumed 1883 deposits. Several
buried and thus older deposits of similar thickness are imaged. The uppermost sediments are
dominated by hemipelagic green muds with little organic matter and high ash content. Intercalated
turbidite and volcanic ash layers are frequent. Modern sedimentation is controlled by strong
currents. The seismic data show widespread occurrence of gas and water column imaging reveals
active venting from the seafloor in numerous locations. The bio-optical measurements of the
surface water and the water color along the transect provided high-resolution datasets of important
oceanographic parameters, such as salinity, water turbidity, and color as well as phytoplankton
biomass. They showed comparatively constant conditions along the transect, as is typical for the
nutrient-poor, open areas of the ocean.

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