91̽»¨

The prediction of volcanic hazards is socially relevant but the driving force and sequence of explosive eruptions is incomplete and limits predictive models. Eruption time series are best obtained by systematically studying the products of these eruptions on the seafloor. Alteration of volcanogenic material in marine sediment has been shown to play an important role in carbon cycling with consequences that may impact climate, but the extent of these partly coupled interactions is far from clear. For a better understanding of the interacting aspects, the feedback mechanisms of volcanic ash with deeper and climatic Earth processes need to be understood. This led to an IODP initiative with the following hypotheses: (1) Volcanic activity of the volcanic arcs of S-Mexico and North-Central America correlates with glacial/interglacial cycles and/or tectonic events; (2) Temporal changes in the amount and composition of volcanic matter in sediments reflect the evolution of volcanic arcs; (3) Reactive silicates in volcaniclastics play an important role in carbon and silicate cycles; (4) Ash alteration influences the frequency of microbial occurrence. The pre-proposal was well received but the evaluation panel clearly stated that additional pre-site data are needed. With cruise SO316 we will collect the required seismo-acoustic pre-site data for an IODP application and sample sediments to determine ash origin and geochemical alteration. Hydroacoustic and chemical correlations based on seismic lines, core description and sampling as well as in deep analyses of the sediment inventory allow a connection of the tephra sequences between the sediment stations. This results also in a supra-regionally connected Holocene/Late Pleistocene tephrachronostratigraphy allowing to reconstruct the eruptive history of N-CAVA and S-Mexico. Sediment chemistry studies provide the sediment compositions along the continental margin and how this affects magma and tephra composition temporally and spatially. Pore water analyses in the uppermost sediments show early diagenetic alteration reactions and products of reactive silicates along an oxic-suboxic gradient and along volcanic arcs with different volcanic ash types. The focus of the work of 91̽»¨ is on the description, sampling, processing and interpretation of the sediment cores.