Pure biogenic opal ooze came to show, which are composed of diatom skeletons. These diatoms are growing in huge numbers in the surface waters of the Southern Ocean, south of the Polar Front, and after death, their skeletons are deposited on the sea floor along the so-called Opal Belt. Especially obvious in our core are the mats of the diatom genus Thalassiotrix, which are built from needle-like cell covers of biogenic opal and if appearing with a single species in the sediment core, look like wet paper tissues. The pure opal ooze is strongly coloured in some layers by metal sulphides, documenting the hydrothermal activity in the caldera over time. On Monday, 13th of May, we sampled  sediments by piston corer about 60 km to the west of the Kemp Caldera on the eastern flank of the ridge segment E8 (Fig. 2). The sediments of the 8.70 m long core had high contents of volcanic components and our geochemists are interested in investigating the influence of the hydrothermal activity and especially that of the iron geochemistry. Based on these interests, pore water samples were taken every 10 cm along the length of the core to measure alkalinity and iron concentrations already on board. Further nutrients and specific dissolved components will be analysed after the expeditions in the labs of the home institutes.

On Tuesday, 14th of May, the Kemp Caldera was back in the centre of our research. Several CTD and water rosette stations were taken near the hydrothermal area, in the caldera centre and on the rim area. Based on anomalies of turbidity, redox potential, temperature and methane content we wanted to analayse the influence of the active hydrothermal area on the seawater chemistry. A ROV dive followed located at the northern, inner rim of the Kemp Caldera in 1100 m depth, over an area where we had detected gas bubble streams several times in the water column. Diving with ROV Quest, we were unable to find the original exit of the gas bubbles on the seafloor, and therefore we concentrated our efforts on sampling the hydrothermal fluids of new discovered smokers. A black smoker, which fluid temperatures were measured as 230° C (Fig. 3), had a high iron concentration and the lowest pH values of 2.3, while a second chimney which we sampled had a temperature of 200° C contained almost no iron and had a pH of 5.5. We have to wait until after the detailed fluid analyses at home to find out if the fluid chemistry is in line with the precipitate content.