Abstract
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We demonstrate the utility of uranium-series age dating using laser ablation multi-collector inductively
coupled plasma mass spectrometry (LA MC-ICPMS) to ‘range find’ a large suite of fossil corals in order to
select those for subsequent detailed and high resolution paleoclimatological analyses. The high abundance
of unaltered and long-lived (100e200 years) microatolls on Kiritimati Island, Kiribati, offers the
exciting prospect of constructing a millennial, if not continuous, coral paleoclimate record for the central
Pacific spanning the period from the mid-Holocene to present. However, with a multitude of collected
corals and Kiritimati sample sites, we required an efficient, cost-effective and reliable analytical method
to optimize selection of quality coral belonging to a prescribed age. Two modern and 41 fossil microatoll
corals from Kiritimati were analysed by the range-finding LA MC-ICPMS technique with a subset also
analysed by high-precision solution MC-ICPMS and AMS radiocarbon to assess the reliability and
accuracy of the laser ablation technique. Coral ages ranged from 6400 to 900 yr BP and laser ablation age
precisions, constrained by the low 230Th count rate, ranged from 9 to 45% at the 2SE level. These ages
generally agreed with ages measured by solution U-series and AMS 14C. However, conflicting results for
(234U/238U)initial in samples analysed by LA- and solution-MC-ICPMS indicates that the laser ablation
method may not be as suitable as previously thought for detecting subtle geochemical alteration. With
40e50 sample analyses per day, the laser ablation method offers a rapid, efficient and cost-effective
means to histogram coral ages with multi-centennial accuracy, even at such low 230Th count rates typical
for young Holocene samples. In addition to in situ corals, the LA MC-ICPMS technique could be further
applied to corals recovered from drill core.