Benthic foraminiferal assemblages as indicators of the paleoceanographic conditions in the eastern Equatorial Pacific

Five assemblages of benthic foraminifers reflecting the changes in the properties of the intermediate water masses and the biological productivity during different periods of the last glacial-interglacial cycle are defined based on the abundances and relative contents of indicative species in the upper 9 m of giant Core MD02-2529 from the Cocos Ridge. High bioproductivity and low oxygen content in the bottom water layer and sediments are established for the interstadial period based on the high abundance of the species Uvigerina peregrina, U. hispida, and C. pachyderma (Assemblage I) and especially for the Last Glacial Maximum (Assemblage II) with the dominant role of the same species and E. smithi. The transition from the glaciation to the current interglacial (Termination I, Assemblage III) is characterized by a high share of the epifaunal species C. wuellerstorfi and H. subhaidingeri, which indicates enhanced hydrodynamic activity and ventilation of the intermediate water washing the bottom. The end of Termination I was marked by strengthened selective dissolution of carbonate microfossils due to the increased influx of fresh organic matter to the bottom and/or advection of more aggressive intermediate waters. The diverse Early Holocene assemblage (Assemblage IV) points to variable ecological niches, while the abundance of the infaunal U. hispida in Assemblage V indicates low productivity of the surface waters and a low oxygen concentration in the bottom sediments of the Late Holocene.