Global simulation of dissolved <sup>231</sup>Pa and <sup>230</sup>Th in the ocean and the sedimentary <sup>231</sup>Pa∕<sup>230</sup>Th ratios with the ocean general circulation model COCO ver4.0
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Published:2022-03-10
Issue:5
Volume:15
Page:2013-2033
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ISSN:1991-9603
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Container-title:Geoscientific Model Development
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language:en
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Short-container-title:Geosci. Model Dev.
Author:
Sasaki Yusuke, Kobayashi HidetakaORCID, Oka Akira
Abstract
Abstract. Sedimentary 231Pa/230Th ratios provide clues to estimate
the strength of past ocean circulation. For its estimation, understanding
the processes controlling the distributions of 231Pa and 230Th in
the ocean is important. However, simulations of dissolved and particulate
231Pa and 230Th in the modern ocean, recently obtained from the
GEOTRACES project, remain challenging. Here we report a model simulation of
231Pa and 230Th in the global ocean with COCO ver4.0. Starting
from the basic water-column reversible scavenging model, we also introduced
the bottom scavenging and the dependence of scavenging efficiency on
particle concentration. As demonstrated in a previous study, the
incorporation of bottom scavenging improves the simulated distribution of
dissolved 231Pa and 230Th in the deep ocean, which has been
overestimated in models not considering the bottom scavenging. We further
demonstrate that introducing the dependence of scavenging efficiency on
particle concentration results in a high concentration of dissolved
230Th in the Southern Ocean as observed in the GEOTRACES data. Our best
simulation can well reproduce not only the oceanic distribution of
231Pa and 230Th but also the sedimentary 231Pa/230Th
ratios. Sensitivity analysis reveals that oceanic advection of 231Pa
primarily determines sedimentary 231Pa/230Th ratios. On the other
hand, 230Th advection and bottom scavenging have an opposite effect to
231Pa advection on the sedimentary 231Pa/230Th ratios,
reducing their latitudinal contrast. Our best simulation shows the realistic
residence times of 231Pa and 230Th, but simulation without bottom
scavenging and dependence of scavenging efficiency on particle concentration
significantly overestimates the residence times for both 231Pa and
230Th in spite of similar distribution of sedimentary
231Pa/230Th ratios to our best simulation.
Funder
Japan Society for the Promotion of Science
Publisher
Copernicus GmbH
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