Central Equatorial Pacific benthic foraminifera during the mid-Brunhes dissolution interval: Ballasting of particulate organic matter by biogenic silica and carbonate

Abstract

Abstract We evaluated the response of Quaternary abyssal benthic foraminifera in cores PC5101 (2o00.86′N, 131o34.32′W) and PC5103 (6o00.10′N, 131o28.57′W) of the Central Equatorial Pacific Ocean to the environmental changes over the past ∼520 kyrs, focusing on the mid-Brunhes dissolution interval (∼533–191 ka). We used multi-dimensional scaling (MDS) to derive MDS axis 1, reflecting food supply from low (negative scores) to high (positive scores) amounts, and MDS axis 2, reflecting variability in the food supply. From ∼120 ka on, Epistominella exigua, an indicator of variable food supply, was more abundant in core PC5103 (∼6oN) than in core PC5101 (∼2oN), but this was reversed from ∼300 to 250 ka. In core PC5101, MDS axis 1 scores are negatively correlated to the biogenic opal mass accumulation rates (MAR) after 249.6 ka, i.e., lower food supply at higher opal-MAR. In contrast, MDS axis 1 scores are positively correlated to the CaCO3-MAR from 520.8 to 331.2 ka. Both carbonate and opal skeletons might ballast particulate organic matter (POM) to enhance food supply to the benthos, but our data indicate that carbonate is more efficient and that changes in dominant ballasting of POM by different biominerals thus may have significantly affected the biological pump. During the transitional period (∼327.5–257.1 ka), ballasting of POM changed from control by calcareous plankton to control by siliceous plankton, with a transient period during which the latitudinal pattern of the Intertropical Convergence Zone was opposite to its modern pattern, with the more variable food supply at\u202f∼\u202f6oN.