Deep-sea benthic foraminifera and biogenic opal: Glacial to postglacial productivity changes in the western equatorial Pacific

Abstract

The accumulation rate of benthic foraminifera in deep-sea sediments is strongly correlated with the productivity of the surface ocean. Core tops from diverse deep-sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor ( J sf-flux) and the benthic foraminifera accumulation rate ( BFAR). The correlation can be used to reconstruct organic carbon flux to the seafloor in the past, and hence the productivity of past oceans. These results are compared with the accumulation rates of carbonate and biogenic opal in the sediments. It is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate. The appropriate equations are derived for the equatorial Pacific, using ☐ core material from Eurydice (ERDC), Indomed (INMD), and Pleiades (PLDS) expeditions. These equations are then applied to two selected time horizons in sediments from the Ontong Java Plateau, a western equatorial Pacific pelagic depth transect, the last transition ( LT), and the last glacial ( LG). It is found that productivity was higher during the last glacial relative to the late Holocene, by a factor between 1.6 and 2. During the last transition productivity was intermediate between glacial and recent values. We do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial. This observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time.