Linke, Peter, ed. (2011) FS SONNE Fahrtbericht / Cruise Report SO210 ChiFlux : Identification and investigation of fluid flux, mass wasting and sediments in the forearc of the central Chilean subduction zone, Valparaiso - Valparaiso, 23.09.-01.11.2010. . IFM-GEOMAR Report, 44 . IFM-GEOMAR, Kiel, 103 pp. DOI 10.3289/IFM-GEOMAR_Rep_44_2011.

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Abstract

Cruise SO210 with RV SONNE to the active continental margin off Chile was conducted by
shiptime exchange with RV METEOR. Funds for mobilizing the research team were provided
by the German Science Foundation (DFG) in conjunction with the Collaborative Research
Centre (SFB) 574 of the University of Kiel. In the first years, the SFB 574 investigated the
pathways and fluxes of volatiles through the erosive subduction zone off Central America. For
comparison, the studies were extended to the accretionary margin off Central Chile. Cruise
SO210 is the last cruise conducted in the framework of SFB 574 and based on investigations
of previous SFB-cruises on the RVs VIDAL GORMAZ and JAMES COOK. The first leg of
cruise SO210 was dedicated to long gravity coring for volcanic ash layers from the erruptive
Southern Volcanic Zone (SVZ) of the Andes that were either deposited as fallouts onto the
incoming Nazca Plate or transported down the slope and across the Chile Trench. Eight gravity
cores of 12 m length were retrieved seaward of the Chile Channel on the outer rise of the
Nazca Plate. The second goal for coring was the description and dating of previously mapped
submarine landslides as well as retrieval of slide-related material for geo-technical
experiments. As the deployment frame for long coring had to be removed on the second leg we
continued coring for mass-wasting and geochemistry with short cores. Ten gravity cores of 3
or 6 m barrel length were retrieved upslope of slides, the glide plane and redeposited material
downslope of the slide evacuation area. This sampling activity was supported by detailed
acoustic surveys with Parasound and multibeam to remap critical areas for mass wasting in
search for events, e.g. triggered by the recent Mw 8.8 Maule Earthquake, such as flanks of
submarine canyons or previously detected submarine slides and to fill data gaps in the existing
bathymetric data. The major activity of the entire cruise was dedicated to the search and
detailed sampling of manifestations of fluid discharge activity on the Chilean forearc. A total
of 11 deployments with the video sled OFOS and 12 dives by the ROV KIEL 6000 were
conducted for ground-truthing of information which indicated possible seep activity and has
been obtained during previous cruises to the Chilean forearc. In five working areas we found
manifestations of fluid discharge. In these areas the survey was followed by an intense
sampling of bottom water, sediments, carbonates, mega and meiofauna and the deployment of
instrumentation on the seafloor. The goal of these deployments was to measure in situ seabed
methane emission rates and associated fluxes of sulfide and major electron acceptors such as
oxygen at seep sites along the Chilean margin and to understand its controls. This was
accompanied by CTD casts to trace oxygen and the fate of methane discharge in the water
column. Sediment cores obtained by multicorer or ROV were used for the geochemical
characterization of the pore water and microbiological studies which include turnover rate
measurements, molecular studies, flow through experiments and sampling of active sediments.
Authigenic carbonates obtained by TV-Grab or ROV were sampled for fauna, biomarker
studies and investigations to reconstruct the growth structures, calcification processes and
fluid-pathway systematic. The sampling of sediments and carbonates recovered a unique fauna
with 79 different taxa, several of them appear to be species new to science.

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