• Ocean and Polar Research
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• v.26 no.2
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• pp.175-185
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• 2004

To delineate Late Pleistocene paleoceanographic change of the West Pacific, we analyzed the oxygen and carbon isotopic ratios of two planktonic foraminifera species (G. sacculifer and N. dutertrei) from a piston core (KODOS-313) taken from the West equatorial Pacific, and they are compared with the published results of the East Pacific (ODP site 847 and RC 11-210), in terms of relative amounts and mass accumulation rates of $CaCO_3$ and eolian component, back to marine isotopic stage (MIS) 6. Differences in oxygen and carbon isotope values between two foraminifear species ($0.75%_{\circ}$ in ${\delta}^{18}O$, $0.05%_{\circ}$ in ${\delta}^{13}C$) are less than those of the East Pacific ($1.30%_{\circ}$ in ${\delta}^{18}O$, $0.14%_{\circ}$ in ${\delta}^{13}C$), which indicates smaller vertical contrasts in both temperature and nutrient between mixing-zone and thermocline in the West Pacific. Strong deviation in${\delta}^{18}O$ of G. sacculifer from SPECMAP suggests the carbonate fraction of KODOS-313 was subjected to partial dissolution by bottom water under lysocline. Lower accumulation rates of $CaCO_3$ and eolian component during glacial times are likely due to low sedimentation rate (ave. 0.75 cm/1000 yr) combined with carbonate dissolution in KODOS-313 site. However, the high $CaCO_3$ contents during the glacial periods clearly follow the general pattern of equatorial Pacific ocean.

• Ocean and Polar Research
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• v.41 no.4
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• pp.275-288
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• 2019

We investigated flux, grain size distribution, Nd-Sr isotope composition, mineral composition, and trace metal composition (REEs and Sc) of inorganic silicate fraction (ISF, mainly Asian dust with an unrestricted amount of volcanic materials) deposited during 600~1000 ka across the Mid-Pleistocene Transition at core NPGP 1401-2A (32°01'N, 178°59'E, 5205m) taken from the central part of the North Pacific. Our results reveal about a 2-fold increase in ISF flux after 800 ka, which is associated with an increase in La/Sc and a decrease in mean grain size. Asian dusts are finer than volcanic materials and La/Sc increases with the enhanced contribution of Asian dusts. Thus, increased flux after 800 ka can be explained by the increased contribution of Asian dusts relative to volcanic materials, likely due to an intensified Westerly Jet (WJ) and the drying of the Asian continent after the MPT. Mean grain size of ISF varies systematically in relation to glacial-interglacial cycles with a decrease during glacial stages, which is consistent with the previous results in the study area. Such a cyclical pattern is also attributed to the increase in the relative contribution of Asian dusts over volcanic components in glacial stages due to intensified WJ and drying of the Asian continent. Thus, it can be concluded that climate changes that had occurred across the MPT were similar to those of interglacial to glacial transitions at least in terms of the dust budget. Different from the Shatsky Rise, however, compositional changes associated with glacial-interglacial mean grain size fluctuations are not observed in Nd-Sr isotope ratios and trace element composition in our study of the Hess Rise. This may be attributed to the location of the study site far (> 4,000 km) from the volcanic sources. The volcanic component at the study site comprises less than 10% and varies within 3% over glacial-interglacial cycles. Such a small variation was not enough to imprint geochemical signals.