Late Neogene and Quaternary diversity and taxonomy of subtropical to temperate planktic foraminifera across the Kuroshio Current Extension, northwest Pacific Ocean

• Published in: Micropaleontology 2020-01, Vol.66 (3), p.177-268
• Main Authors: Lam, Adriane R., Leckie, R. Mark
• Format: Article
• Language: English
• ISSN: 0026-2803; 1937-2795
• DOI: 10.47894/mpal.66.3.01

Patterns of diversity in the modern planktic foraminifera indicate a latitudinal diversity gradient (LDG), which peaks in the mid-latitude regions. Plankton distributional patterns are often most strongly associated with temperature and are expected to change in response to expanded tropical water masses. Defining the underlying causes of climatic and oceanographic processes, however, requires detailed, local-scale diversity curves and evolutionary metrics, as well as solid taxonomic concepts of planktic foraminifera, to test the oceanographic processes driving evolution of marine plankton. Currently, diversity estimates for the planktic foraminifera are mainly based on global datasets skewed towards tropical to subtropical sites and conducted at coarse resolutions that hamper investigations of evolutionary processes, especially for short-lived climate perturbations. Here, we present 10-kyr resolution diversity curves and 25-kyr resolution local first appearance and extirpation rates of planktic foraminifera for four Ocean Drilling Program sites that extend from the temperate northern edge of the modern-day position of the Kuroshio Current Extension (KCE) to the tropics. We provide an updated taxonomic review of late Neogene planktic foraminiferal species from within the influence of the KCE. These data allow for investigations of the western Pacific LDG and patterns of evolution through the late Neogene in response to tectonic and climate events. Our results indicate that a mid-latitude diversity peak has been prominent in the western Pacific since at least 12.1 Ma, with highest diversity generally on the northern edge of the KCE. These data contradict previous studies indicating highest diversity is located ±20°, as our data reveal highest diversity for the planktic foraminifera at ±35° N likely due to strong seasonality. Development of the modern North Pacific gyre system due to closure of the Central American Seaway and constriction of the Indonesian Throughflow increased the LDG between the tropics and the northernmost site, likely in response to KCE intensification. Diversity was only slightly affected during the mid-Piacenzian Warm Period (~3.2–2.9 Ma), with diversity gradients between the equatorial site and southernmost mid-latitude sites becoming similar, perhaps indicating a weaker thermal gradient developing in the northwest Pacific as the KCE and warmer waters were displaced northwards. With intensification of Northern Hemisphere glaciation ca