Faithful transfer of radiolarian silicon isotope signatures from water column to sediments in the South China Sea

Zhang, Qiang; Swann, George E.A.; Pashley, Vanessa; Horstwood, Matthew S.A.

Faithful transfer of radiolarian silicon isotope signatures from water column to sediments in the South China Sea

Zhang, Qiang; Swann, George E.A. ORCID: https://orcid.org/0000-0002-4750-9504; Pashley, Vanessa; Horstwood, Matthew S.A.. 2025 Faithful transfer of radiolarian silicon isotope signatures from water column to sediments in the South China Sea. Biogeosciences, 22 (14). 3533-3546. 10.5194/bg-22-3533-2025

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Official URL: https://doi.org/10.5194/bg-22-3533-2025

Abstract/Summary

Radiolarian silicon isotopes (δ30Sirad) hold significant potential as a proxy for constraining past silicon cycling in seawater. However, the extent to which δ30Sirad signatures in sediments accurately represent the isotopic signals of the overlying water column remains unclear, particularly under the influence of radiolarian shell dissolution during sinking and burial in the sediment record. This study presents the first comparative analysis of δ30Sirad compositions and the radiolarian assemblage community using water column and surface sediment samples collected from the South China Sea (SCS). The results indicate that δ30Sirad values range from 1.56 ‰–1.83 ‰ (mean = 1.74 ‰) in the water column and from 1.61 ‰–1.85 ‰ (mean = 1.73 ‰) in surface sediments, with the fractionation factor for δ30Sirad varying from −0.33 ‰ to −0.92 ‰ (mean = −0.58 ‰). δ30Sirad signatures in the water column are primarily contributed to by radiolarians from the 0–100 m water depth layer. No significant discrepancies in δ30Sirad values were observed between plankton and sediment samples at each sampling station, as evidenced by the paired t test (p = 0.75), implying that dissolution has a minimal impact on δ30Sirad during the transfer of radiolarian shells to the sediment record. This finding may be enhanced by the dominance of more dissolution-resistant Spumellaria and Nassellaria taxa (> 99 % relative abundance) within the radiolarian community, coupled with the scarcity or absence of the readily dissolvable radiolarian taxa in the analysed samples. This study demonstrates the faithful preservation of the δ30Sirad signature and its potential for studying past changes in the marine silicon cycle.

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.5194/bg-22-3533-2025

ISSN:

1726-4189

Date made live:

23 Sep 2025 10:03 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/540273