Abstract

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.

Highlights

  • The decrease in atmospheric CO2 concentrations from interglacial to glacial stages has occurred repeatedly, coinciding with Milankovitch solar insolation cycles (Sigman and Boyle 2000)

  • The age model for PC5103 was determined by matching the oxygen isotope record of planktonic foraminifera (Globigerinoides sacculifer) to the LR04 stacks (Lisiecki and Raymo 2005) because the SPECMAP record only extends to 780 ka (Fig. 2a)

  • These findings suggest that the dominant factors influencing biogenic CaCO3 and opal abundances have consistently affected both the northern (PC5103) and southern (PC5101) sites in the central equatorial Pacific

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Summary

Introduction

The decrease in atmospheric CO2 concentrations from interglacial to glacial stages has occurred repeatedly, coinciding with Milankovitch solar insolation cycles (Sigman and Boyle 2000). One of the most striking features used to elucidate the missing atmospheric CO2 related to paleoclimatic change is the quasi-regular variability pattern in the biogenic (CaCO3 and opal) content of Pleistocene marine sediment in the Equatorial Pacific (e.g., Anderson et al 2008). The Equatorial Pacific CaCO3 cycles, with higher contents during glacial than interglacial periods, reflect a preservation-production signal, where the oceans are more productive during glacial times (e.g., Lyle et al 1988; Archer 1991; Herguera and Berger 1991; Murray et al 1993). In general, the Pacific CaCO3 cycles appear to be influenced by the corrosiveness of deep water, which reflects a preservation-dissolution signal where the oceans are less corrosive during glacial times (e.g., Farrell and Prell 1989; Wu and Berger 1989; Hebbeln et al 1990; Le and Shackleton 1992)

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