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230Th Normalization: New Insights on an Essential Tool for Quantifying Sedimentary Fluxes in the Modern and Quaternary Ocean

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Pichat,  Sylvain
Terrestrial Palaeoclimates, Max Planck Institute for Chemistry, Max Planck Society;

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Citation

Costa, K. M., Hayes, C. T., Anderson, R. F., Pavia, F. J., Bausch, A., Deng, F., et al. (2020). 230Th Normalization: New Insights on an Essential Tool for Quantifying Sedimentary Fluxes in the Modern and Quaternary Ocean. Paleoceanography and paleoclimatology, 35(2): UNSP e2019PA003820. doi:10.1029/2019PA003820.


Cite as: https://hdl.handle.net/21.11116/0000-0007-4B57-4
Abstract
230
Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution
sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever
more diverse marine environments, the nuances of
230
Th systematics, with regard to particle type, particle
size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000
sedimentary records of
230
Th from across the global ocean at two time slices, the late Holocene (0–5,000
years ago, or 0–5 ka) and the Last Glacial Maximum (18.5 –23.5 ka), and investigated the spatial structure of
230
Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during
the Last Glacial Maximum (1.79–2.17 g/cm
2
kyr, 95% confidence) relative to the Holocene (1.48–1.68
g/cm
2
kyr, 95% confidence). We then examined the potential confounding influences of boundary
scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and
carbonate dissolution on the efficacy of
230
Th as a constant flux proxy. Anomalous
230
Th behavior is
sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes
and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that
230
Th normalization is a robust tool for
determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m
water depth).