Biogenic CaCO3 and Opal Depositions and Their Latitudinal Comparison During the Past 600 ka in the Central Equatorial Pacific

The orbital-scale variations in biogenic CaCO_3 and opal abundance in two piston cores collected in the central equatorial Pacific (core PC5101 from a southern site at 2°N, and core PC5103 from a northern site at 6°N) were compared to assess latitudinal differences. The correlation between the oxygen isotope stratigraphy of planktonic foraminifera (＂Globigerinoides sacculifer＂) of PC5103 with the LR04 stacks provides the age of PC5103 to be approximately 950 ka. The age of PC5103 was further refined by correlating the CaCO_3 content with the well-dated core RC11-210. The age of PC5101 was also constrained by the same CaCO_3 chronostratigraphic correlation with RC11-210, resulting in an age of approximately 650 ka. Distinct orbital-scale series of CaCO_3 and opal variations appear to be parallel between the two cores during the past 600 ka, which are controlled mainly by eccentricity with an approximate periodicity of 100 ka. It is worth noting that the biogenic CaCO_3 and opal deposition patterns in the two cores differ between interglacial and glacial periods. During interglacial periods the biogenic opal content is higher in the southern core than in the northern core, which corresponds with the present-day condition. In contrast the CaCO_3 content is higher in the northern core, which is contradictory to the present-day northward decreasing CaCO_3 deposition pattern from the Equator. The collection site of PC5101 is approximately 350 m deeper than that of PC5103, which significantly promotes CaCO_3 dissolution and causes unexpectedly high CaCO_3 content at the northern site in contrast to the biogenic opal content.