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 CaCO3 and opal abundance in two piston cores collected in the central equato- rial 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 CaCO3 content with the well-dated core RC11-210. The age of PC5101 was also constrained by the same CaCO3 chronostratigraphic correlation with RC11-210, resulting in an age of approximately 650 ka. Distinct orbital-scale series of CaCO3 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 CaCO3 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 condi- tion. In contrast the CaCO3 content is higher in the northern core, which is contradictory to the present-day northward decreas- ing CaCO3 deposition pattern from the Equator. The collection site of PC5101 is approximately 350 m deeper than that of PC5103, which significantly promotes CaCO3 dissolution and causes unexpectedly high CaCO3 content at the northern site in contrast to the biogenic opal content.

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