Nitrogen isotope ratios (δ15N) of surface sediment in the equatorial ocean reflect the mode of upper water circulation pattern. We applied this knowledge to reconstruct glacial-interglacial variations of an upwelling field in western equatorial Pacific using δ15N from sediment cores. Distinct minima in δ15N values were found corresponding to glacial periods on the northern and eastern edges of the upwelling field (Mindanao Dome), indicating glacial enlargement of upwelling due to enhanced winter monsoon activity. However, at a site on southern side of the upwelling region, minima in δ15N values were obtained during interglacial periods. These opposing variations in δ15N values could be interpreted as a northward shift of the upwelling zone, during glacial periods. The glacial-interglacial migration of the circulation pattern in this region may reflect a modal change in the global thermohaline circulation (conveyor belt) during glaciation.
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