Distribution and ecology of the Globigerinoides ruber — Globigerinoides elongatus morphotypes in the Azores region during the late Pleistocene-Holocene

Globigerinoides ruber is the dominant taxon in the North Atlantic Subtropical Gyre, nowadays limited to the north by the Azores Current. It is highly sensitive to recent and late Pleistocene Azores Front Current System variability. In this study, we analyse the distribution of five individual morphotypes of the G. ruber – G. elongatus plexus (G. ruber s.s., G. ruber cyclostoma type, G. elongatus, G. elongatus cf.1, G. elongatus pyramidical type) and G. ruber kummerform gr. in a core (ATA13-OF-KT1) collected southwest of the Azores islands and located in a strategical position near the present-day boundary of the Subtropical Gyre/Azores Front Current System (STG/AFCS). Micropaleontological and stable isotope analyses can provide new insights on the ecological preferences of the G. ruber chromotypes and some selected morphotypes (especially the less studied G. ruber cyclostoma type). Their distribution pattern shows cyclic oscillations linked to climatic variability at orbital and millennial scales. G. elongatus clearly dominated the G. ruber - G. elongatus assemblage during the interglacials, while G. ruber cyclostoma type reached their maxima abundances during glacial periods. Furthermore, changes in the relative abundance of warm (G. elongatus) and cool water (G. ruber cyclostoma type) morphotypes represent a powerful tool to track the position occupied by the Subtropical Gyre/Azores Current (STG/AC) boundary during the last 74.7 kyr.