Kürzinger, Victoria

Vent precipitates of hydrothermally active systems in the Scotia Sea – formation of elemental sulfur in the Kemp Caldera

The South Sandwich island arc is a volcanically active intra-oceanic arc situated in the Scotia Sea, which is part of the South Atlantic Ocean. This is­land arc is for­ming as a re­sult of the sub­duc­tion of the South Ame­ri­can pla­te un­der the Sand­wich mi­cro-pla­te. Fur­ther­mo­re, the in­ter-ocea­nic back-arc sprea­ding East Sco­tia Ridge (ESR), which is as­so­cia­ted with the sub­duc­tion zone as well, is lo­ca­ted in the west of the South Sand­wich is­land arc and con­sists of ten ridge seg­ments (E1-E10). Spe­ci­fi­cal­ly in E2 and E9, hydro­ther­mal­ly ac­tive sites are known, oc­cur­ring as ac­tive­ly ven­ting chim­neys. In ad­di­ti­on, hydro­ther­mal ac­tivi­ty is also re­cor­ded from the vol­ca­nic is­land arc set­ting.

The sub­ma­ri­ne cal­de­ra west of Kemp Se­a­m­ount is of par­ti­cu­lar in­te­rest. This area is known as Kemp Cal­de­ra and was dis­co­ve­r­ed du­ring a geo­phy­si­cal sur­vey of the re­se­arch crui­se JR224 in 2009. A re­mar­ka­ble seaf­loor fea­ture in the midd­le of the cal­de­ra is a cone, in­ter­pre­ted as re­sur­gent cone. Extinct chim­neys and whi­te smo­ker vent fiel­ds are located around this cone but are po­or­ly imaged in the seafloor ba­thy­me­try.

A special feature of the Kemp Caldera is the occurrence of elemental sulfur (S⁰) at pH-values > 5, which contradicts the formation of sulfur by SO₂ disproportionation. Furthermore, the occurrence of S⁰ with sulfide minerals is rather uncommon. In Kemp Caldera, however, these minerals coexist and occur probably in equilibrium. The formation of elemental (liquid) sulfur in hydrothermal systems at moderate pH-values is still unclear. Additionally, δ³⁴S values of the Kemp Caldera hydrothermal system are all positive and thus too high to result from disproportionation, making this caldera special.

My PhD work is part of the MARUM “Clus­ter of Ex­cel­lence” in the ge­ne­ral area “The Oce­an Floor as Re­ac­tor”. In this project, I focus first of all on the determination and differentiation of the hydrothermal precipitates found in the Scotia Sea, especially in the Kemp Caldera. To get a better insight into the formation processes of S⁰, experiments under hydrothermal conditions using a Dickson-type reactor are performed and studied in more detail. Thus, I want to enhance the understanding of the genesis of these precipitates, especially the formation of elemental sulfur, and the submarine caldera itself. Therefore, a geological map of the Kemp Caldera is necessary and would be very useful to get an overview and better understanding of the morphology and the geological setting.