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Moore, MD, Charles CD, Rubenstone JL, Fairbanks RG.  2000.  U/Th-dated sclerosponges from the Indonesian Seaway record subsurface adjustments to west Pacific winds. Paleoceanography. 15:404-416.   10.1029/1999pa000396   AbstractWebsite

Stable isotope records from sclerosponges collected at 10-20 m depth in the Indonesian Seaway and Solomon Islands are particularly well suited for reconstructing century-scale trends in ambient temperature variability and the oceanic uptake of fossil fuel carbon. Basal U/Th dates demonstrate that the sclerosponges analyzed are 85-100 years old. Isotopic records from the Indonesian specimens suggest a strong subsurface cooling over the past 20 years that is not manifested in either surface instrumental or shallower coral proxy records. However, analysis of observed subsurface temperatures in Indonesia, observed winds in the west Pacific, and simulated subsurface temperatures from a steady state general circulation model hindcast forced by observed winds combine to suggest that thermocline adjustments could account for at least part of the recent cooling inferred from the Indonesian sclerosponges. If so, the sclerosponge data suggests that, on average, the west Pacific thermocline has shoaled significantly over at least the past 2 decades.

Cobb, KM, Charles CD, Cheng H, Kastner M, Edwards RL.  2003.  U/Th-dating living and young fossil corals from the central tropical Pacific. Earth and Planetary Science Letters. 210:91-103.   10.1016/s0012-821x(03)00138-9   AbstractWebsite

This study evaluates the accuracy of U/Th dates for young (< a few thousand years old) reef corals, both living and fossil, and explores strategies for refining those dates. The high precision of the U/Th method (+/-1-2%) for dating young corals is well-established. Earlier studies have demonstrated the method's accuracy for select samples of known age. However, these studies have focused on typical samples that have extremely low Th-232 concentrations (tens of pg/ g). Here we study the dating systematics of young corals that have low but significant amounts of Th-232 (up to 1000 pg/g), indicating the presence of small fractions of non-radiogenic Th-230 (i.e. Th-230 not generated by in situ U decay). We report U/Th ages for living and subaerially exposed fossil corals from Palmyra Island, located in the central tropical Pacific, that range from 50 to 700 yr old. The Palmyra corals contain varying amounts of Th-232 and small fractions of associated non-radiogenic Th-230. Uncertainty associated with the correction for non-radiogenic Th-230 can lead to significant errors in U/Th dates. We have characterized non-radiogenic Th-230/Th-232 values, (Th-230/Th-232)(nr), as a means of minimizing this source of error. We calculate (Th-230/Th-232)(nr), values ranging from 0 to 2 X 10(-5) for the Palmyra living corals by comparing measured U/Th dates to absolute dates for the living coral, whose chronology is well-established. For the fossil corals, we employ three different approaches to arrive at (Th-230/Th-232)(nr) estimates. First, we compare measured U/Th dates to absolute dates in samples from a young fossil coral that overlaps the living coral. Next, we use the firm relative dating constraints imposed by five overlapping fossil corals from the 14th-15th centuries to calculate (Th-230/Th-232)(nr) values. Finally, we attempt to anchor the 14th-15th century floating coral chronology to an absolute chronology by correlating the climate signals in the coral records to those in absolutely dated climate proxy records. All lines of evidence point to a range of (Th-230/Th-232)(nr) for fossil corals that overlaps the range determined for the living coral, suggesting that most of the thorium is primary or is added while the coral is still alive. Our work also demonstrates the utility of multiple (Th-230/Th-232)(nr) estimates. Most importantly, we demonstrate a method by which accurate (+/- 5 yr) U/Th-based chronologies can be obtained for young fossil corals with significant Th-232 concentrations.