Sightings of the Rare Globorotalia Cavernula in the Subantarctic South of Africa: Biogeochemical and Ecological Insights

Abstract

Abstract Over 50 years since its discovery and decades since its last recorded sighting in the modern ocean, Globorotalia cavernula has made another appearance: now in Subantarctic plankton tows south of Africa. This finding expands the known modern range of the species, which was commonly thought to be absent from the Atlantic sector of the Southern Ocean. Here, we use high-resolution microscopy and trace element analysis (fs-LA-ICP-MS) as a window into the ecology and habitat of this enigmatic species. Shell-averaged trace element ratios of G. cavernula are consistent with the cool–cold, well-oxygenated, open-ocean waters where it was collected (low Mg/Ca, Mn/Ca); and Sr/Ca is the least variable. Chamber-to-chamber trends are generally similar to other non-spinose species, but absolute values (e.g., Ba/Ca) can differ substantially. Combining our data with previous sightings suggests under-sampling/under-reporting of G. cavernula in the modern/recent Southern Ocean, and possibly an expanded geographic range during the colder Pleistocene Epoch.