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Neodymium isotopic composition and concentration in the Southwest Pacific Ocean

HIROSHI AMAKAWA, HIROFUMI TAZOE, HAJIME OBATA, TOSHITAKA GAMO, YUJI SANO, CHUAN-CHOU SHEN
Geochemical Journal, Vol. 47, No. 4, P. 409-422, 2013

ABSTRACT

We report two vertical profiles of the concentration and isotopic composition of neodymium (Nd) in seawater samples collected at 20°S and 30°S along a longitude of 170°W in the Southwest Pacific Ocean. At depths below 500 m, Nd isotopic composition values are less radiogenic than those obtained from the subtropical North Pacific. The minimum εNd values of -8.0 and -6.9 at depths of 800 to 1000 m correspond to Antarctic Intermediate Water (AAIW). The differences in εNd values between upper deep water (2000-3000 m) and lower deep water (>4000 m) seem to be associated with Upper and Lower Circumpolar Deep Waters (UCDW and LCDW, respectively). The radiogenic Nd supply to AAIW from the Society Islands is estimated to be 30 ± 22 tons Nd/yr, which is consistent with the estimates from previous studies conducted in the same location and the oceanic region close to the Hawaiian Islands. Our study demonstrates the uniqueness of Nd isotopic composition distributions in the Southwest Pacific Ocean. These results may be valuable for tracing present and past ocean circulation in this region.

KEYWORDS

Southwest Pacific, Nd isotopic composition, Antarctic Intermediate Water (AAIW), Upper and Lower Circumpolar Deep Waters (UCDW and LCDW), GEOTRACES

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