Sedimentary facies and invertebrate faunal exchange confirm humid conditions in the tropical eastern Atlantic during interglacial Marine Isotopic Stage (MIS) 11c

The geological study of Marine Isotopic Stage (MIS) 11c (424–397 ka) is key to reconstructing the climatic and oceanographic conditions during one of the longest and the warmest interglacial in the last 1 million years. Moreover, interglacial MIS 11c is considered as an important analogue for our near future in times of climate change, under anthropogenic emissions scenarios, due to its similar orbital forcing configuration. Here we present the results of a comprehensive analysis of one of the most extensive Quaternary fossiliferous sedimentary successions in the Cabo Verde archipelago in the tropical northeastern Atlantic. The Nossa Senhora da Luz Bay (Santiago Island) is one of the few MIS 11 fossiliferous sites known in Macaronesia. The sedimentary succession records a set of transitions between fluvial and marine environments, and emersion and immersion events within a confined, highly protected bay environment. A thick layer of fine-branched rhodoliths in its upper part suggests ecological conditions that no longer exist in Cabo Verde. The presence of specimens of the intertidal clam Senilia senilis in life position ∼12 m above present-day mean sea level leads us to reinterpret the relative sea-level changes at Santiago Island and show that the uplift trend since MIS 11c is an order of magnitude lower (0.01 mm/yr) than previously calculated (0.10 to 0.14 mm/yr). The fossil assemblage includes representatives of five phyla, with molluscs being the most diverse and abundant. Despite the abundance of some bivalves (Saccostrea cuccullata, S. senilis, and Aequipecten opercularis), and gastropods (Thetystrombus latus and Thais nodosa), and some horizons showing the crustacean burrows Thalassinoides suevicus, the general biodiversity is low. The presence of S. cuccullata and S. senilis, both absent from present-day Cabo Verde archipelago, indicates a tropical, more humid climate in this region, during MIS 11c.