Introduction 3 Background 6 Scientific objectives 8 Operations and coring strategy 17 Site summaries 45 Preliminary scientific assessment 47 References

The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event of 5–6 °C around 56 million years ago caused by input of carbon into the ocean and atmosphere. Hydrothermal venting of greenhouse gases produced in contact aureoles surrounding magmatic intrusions in the North Atlantic Igneous Province have been proposed to play a key role in the PETM carbon-cycle perturbation, but the precise timing, magnitude and climatic impact of such venting remains uncertain. Here we present seismic data and the results of a five-borehole transect sampling the crater of a hydrothermal vent complex in the Northeast Atlantic. Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of the index taxon Apectodinium augustum in the vent crater, firmly tying the infill to the PETM. The shape of the crater and stratified sediments suggests large-scale explosive gas release during the initial phase of vent formation followed by rapid, but largely undisturbed, diatomite-rich infill. Moreover, we show that these vents erupted in very shallow water across the North Atlantic Igneous Province, such that volatile emissions would have entered the atmosphere almost directly without oxidation to CO2 and at the onset of the PETM.

Kikai submarine caldera to the south of the Kyushu Island, SW Japan, collapsed at 7.3 ka during the latest supereruption (>500 km3 of magma) in the Japanese Archipelago. Multi functional research surveys of the T/S Fukae Maru in this caldera, including multi-beam echosounder mapping, remotely operated vehicle observation, multi-channel seismic reflection survey, and rock sampling by dredging and diving, provided lines of evidence for creation of a giant rhyolite lava dome (~32 km3) after the caldera collapse. This dome is still active as water column anomalies accompanied by bubbling from its surface are observed. Chemical characteristics of dome-forming rhyolites akin to those of presently active small volcanic cones are different from those of supereruption. The voluminous post-caldera activity is thus not caused simply by squeezing the remnant of syn-caldera magma but may tap a magma system that has evolved both chemically and physically since the 7.3-ka supereruption.

The emplacement temperatures of accidental and juvenile fragments in the Habushiura pyroclastic density current (PDC) deposit were estimated using analysis of rock magnetism. The Habushiura PDC was generated in a costal or shallow offshore area during the early stage of the AD 886 phreatomagmatic eruption on Niijima Island, Japan. We collected 160 samples from 11 beds, which include three lithofacies types: a massive lapilli tuff (Facies A); a graded and/or diffusely stratified lapilli tuff (Facies B); and a swarm of large pumice (Facies C). Juvenile specimens from Facies A and C show a wide range of emplacement temperatures, from less than 150 °C up to 300 °C, in contrast with the emplacement temperatures lower than 150 °C of Facies B. Morphological features of the ash components and random changes in palaeomagnetic direction by stepwise thermal demagnetization indicate that low-temperature emplacement occurred by phreatomagmatic eruptions and ingestion of ambient air by the turbulent current. The emplacement temperatures of accidental fragments were up to 380 °C, which is higher than juvenile fragments. They are thought to have cooled more slowly than juvenile fragments due to the smaller surface area with respect to their volume.

Contents 1 Background and objectives 3 Operations 5 Lithostratigraphy 9 Biostratigraphy 12 Paleomagnetism 17 Geochemistry 21 Physical properties 24 References