Uranium,
thorium, and protactinium radionuclides in marine sediments
are important proxies for understanding the earth’s environmental
evolution. Conventional solution-based methods, which typically involve
isotope spike preparation, concentrated acid sample digestion, column
chemistry, and mass spectrometry, allow precise but time-consuming
and costly measurements of these nuclide concentrations (i.e., 230Th and 231Pa). In this work, we have established
an efficient method for 230Th and 231Pa measurement
of marine sediments down to the picogram-per-gram level without purification
and enrichment. Our method first transforms a small amount of thermally
decomposed sediments (∼0.1–0.2 g) to homogeneous silicate
glass using a melt quenching technique and then analyzes the glass
with laser ablation multicollector inductively coupled plasma–mass
spectrometry. Standard sample bracketing with isotope-spike-calibrated
glass standards prepared in this study was used to correct for instrumental
fractionation during measurement. It is demonstrated that our method
can accurately determine the U–Th–Pa concentrations
of typical marine sediments in the late Pleistocene with precision
of a few percent. Compared with the conventional solution-based methods,
the turnover time of sample preparation and measurement with our established
protocol is greatly reduced, facilitating future application of U-series
radionuclides in reconstructing oceanic processes at high temporal
and spatial resolution.
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