Shift in biotic response of abyssal benthic foraminifera since MIS 7 in the eastern equatorial Pacific Ocean

摘要

We investigated the late Quaternary abyssal benthic foraminiferal faunas from the upper 209 cm of sediment core (KODOS PC5101) in order to understand the biotic response of abyssal benthic foraminifera to the glacial–interglacial cycle in the eastern equatorial Pacific Ocean. Three factor assemblages were identified in the benthic foraminiferal faunas of core PC5101: the common deep-sea fauna for which there is some seasonal food supply (Factor 1 assemblage), the fauna that suffer from possible carbonate undersaturation in the deep waters of the Southern Ocean or low food supply (Factor 2 assemblage), and the fauna for which there is seasonal food supply (Factor 3 assemblage). The low Horn’s index of overlap indicates the instability of benthic faunal association during the Marine Isotope Stage (MIS) 5. There are reasonably good correlations between the Factor 1 or 2 assemblages and the CaCO3 or biogenic opal content in the earlier part of the studied interval (early MIS 5 to MIS 7), whereas there is no significant correlation in the later part (MIS 1 to late MIS 5), except for a weak correlation between the Factor 1 assemblage and biogenic opal content. It is suggested that carbonate undersaturation at the sediment-water interface on the seafloor was one of major factors that influenced benthic foraminiferal fauna at the site of our study, particularly from early MIS 5 to MIS 7. However, additional factors also affected benthic foraminifera from MIS 1 to late MIS 5. For example, enhanced periodicity of the food supply from the surface ocean (i.e., seasonality or ENSO variability) might be another factor responsible for the shift in the biotic response of abyssal benthic foraminifera deposited after MIS 5.