Seafloor investigations of the Kemp Caldera, the southernmost arc caldera volcano from the South Sandwich Island Arc

Kemp Caldera, situated in the south of the intra-oceanic South Sandwich arc, is one of the least explored submarine calderas that hosts hydrothermally active vent sites. The caldera was discovered in 2009. Since then, the focus has been primarily on biological studies. During the R/V Polarstern cruise PS119 in 2019, we gained new insights into the morphology, petrology and the formation of the Kemp Caldera. The ship's multibeam data provide an overview of the caldera bathymetry and backscatter characteristics. The new data revealed that the caldera is nested with two or possibly three concentric calderas. TV-sled and remotely operated vehicle (ROV) observations provide detailed visual data for the hydrothermally active sites of the vent field at the central resurgent cone and flare site at the NNW caldera rim. The central vent field is dominated by white smokers, where clams, sponges and other fauna thrive, while at the flare site inactive as well as actively venting chimneys have been found. The latter are characterized by metal-enriched fluids of temperatures ≥200°C. During ROV dives, rock samples were collected from the cone, providing the first information about the Kemp Caldera rock composition. The caldera rocks are dacitic, in contrast to the basalts and andesites of the neighboring Kemp Seamount. This suggests that the dacitic cone was formed by one or more later eruptions of differentiated magma, probably stored in shallow intrusions which are driving hydrothermal activity.