Latitudinal change in benthic foraminiferal fauna by ITCZ movement along the similar to 131A degrees W transect in the equatorial Pacific Ocean

Abstract

Modern and fossil benthic foraminifera were examined from nine surface sediments and two piston cores along the similar to 131A degrees W transect in the equatorial Pacific Ocean. This study was conducted to clarify the biotic response of abyssal benthic foraminifera during the last 220 ka to changes in the seasonal extent of the Intertropical Convergence Zone (ITCZ). The abundance of modern benthic foraminifera was high at stations between the equator and 6A degrees N, whereas it was low at stations north of 6A degrees N, which is generally consistent with the latitudinal CaCO3 distribution of surface sediments. The northward increase of Epistominella exigua from the equator to 6A degrees N is similar to the seasonal variations in chlorophyll-a concentrations in the surface water and ITCZ position along 131A degrees W. This species was more common at core PC5103 (6A degrees N) than at core PC5101 (2A degrees N) after 130 ka, when the Shannon-Wiener diversity (H') between the two cores started to diverge. Hence, the presentday latitudinal difference in benthic foraminifera (E. exigua and species diversity) between 2A degrees N and 6A degrees N along 131A degrees W has been generally established since ZZ130 ka. According to the modern relationship between the seasonality of primary production and seasonal ITCZ variations in the northern margin of the ITCZ, the latitudinal divergence of benthic foraminiferal fauna between 2A degrees N and 6A degrees N since 130 ka appear to have been induced by more distinct variations in the seasonal movement of ITCZ.