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Dissolved silicon isotope dynamics in large river estuaries

Zhang, Zhouling ; Cao, Zhimian ; Grasse, Patricia ; Dai, Minhan ; Gao, Lei ; Kuhnert, Henning ; Gledhill, Martha ; Chiessi, Cristiano M. ; Doering, Kristin LU orcid and Frank, Martin (2020) In Geochimica et Cosmochimica Acta 273. p.367-382
Abstract

Estuarine systems are of key importance for the riverine input of silicon (Si) to the ocean, which is a limiting factor of diatom productivity in coastal areas. This study presents a field dataset of surface dissolved Si isotopic compositions (δ30SiSi(OH)4) obtained in the estuaries of three of the world's largest rivers, the Amazon (ARE), Yangtze (YRE), and Pearl (PRE), which cover different climate zones. While δ30SiSi(OH)4 behaved conservatively in the YRE and PRE supporting a dominant control by water mass mixing, significantly increased δ30SiSi(OH)4 signatures due to diatom utilization of Si(OH)4 were observed in the ARE and reflected a Si isotopic... (More)

Estuarine systems are of key importance for the riverine input of silicon (Si) to the ocean, which is a limiting factor of diatom productivity in coastal areas. This study presents a field dataset of surface dissolved Si isotopic compositions (δ30SiSi(OH)4) obtained in the estuaries of three of the world's largest rivers, the Amazon (ARE), Yangtze (YRE), and Pearl (PRE), which cover different climate zones. While δ30SiSi(OH)4 behaved conservatively in the YRE and PRE supporting a dominant control by water mass mixing, significantly increased δ30SiSi(OH)4 signatures due to diatom utilization of Si(OH)4 were observed in the ARE and reflected a Si isotopic enrichment factor 30ε of −1.0 ± 0.4‰ (Rayleigh model) or −1.6 ± 0.4‰ (steady state model). In addition, seasonal variability of Si isotope behavior in the YRE was observed by comparison to previous work and most likely resulted from changes in water residence time, temperature, and light level. Based on the 30ε value obtained for the ARE, we estimate that the global average δ30SiSi(OH)4 entering the ocean is 0.2–0.3‰ higher than that of the rivers due to Si retention in estuaries. This systematic modification of riverine Si isotopic compositions during estuarine mixing, as well as the seasonality of Si isotope dynamics in single estuaries, needs to be taken into account for better constraining the role of large river estuaries in the oceanic Si cycle.

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type
Contribution to journal
publication status
published
subject
keywords
Biological fractionation, Conservative mixing, Large river estuaries, Riverine Si input, Stable Si isotopes
in
Geochimica et Cosmochimica Acta
volume
273
pages
16 pages
publisher
Elsevier
external identifiers
  • scopus:85079043229
ISSN
0016-7037
DOI
10.1016/j.gca.2020.01.028
language
English
LU publication?
no
additional info
Funding Information: This work was funded by the National Natural Science Foundation of China (NSFC; 91858107 and 41606089 ) and by the National Key Scientific Research Project ( 2015CB954003 ) sponsored by the Ministry of Science and Technology of China . Zhouling Zhang was co-supported by a scholarship under the Graduate School of Xiamen University and the National Key Scientific Research Project ( 2015CB954001 ). Henning Kuhnert was supported by the DFG Research Center “The Ocean in the Earth System”. Cristiano M. Chiessi acknowledges the financial support from FAPESP ( 2012/17517-3 ). We thank the R/V Meteor cruise M147 crew and the R/V Maria S. Merian cruise MSM20/3 crew for technical support during sampling in the ARE. Data acquisition and sample collection in the YRE were conducted onboard R/V Runjiang I supported by a Shiptime Sharing Project of the NSFC (NORC2015-03). We thank Guipeng Yang for providing the Chl-a data and Zhiqiang Liu for providing the wind data in the YRE. We thank Kerstin Nachtigall, Andre Mutzberg, Lifang Wang, Biyan He, Wei Qian, Weidong Zhai, Pengfei Liu, and Gila Merschel for their assistance in sampling and/or analysis. We also thank Paul Treguer, Christina De La Rocha, and Shaily Rahman for providing helpful discussion. We would like to thank Damien Cardinal, Gregory de Souza, and two anonymous reviewers for their constructive comments on the manuscript. Publisher Copyright: © 2020 Elsevier Ltd
id
39dd597c-94d1-4036-a301-b255452561d9
date added to LUP
2022-09-05 12:43:51
date last changed
2022-09-15 20:51:02
@article{39dd597c-94d1-4036-a301-b255452561d9,
  abstract     = {{<p>Estuarine systems are of key importance for the riverine input of silicon (Si) to the ocean, which is a limiting factor of diatom productivity in coastal areas. This study presents a field dataset of surface dissolved Si isotopic compositions (δ<sup>30</sup>Si<sub>Si(OH)4</sub>) obtained in the estuaries of three of the world's largest rivers, the Amazon (ARE), Yangtze (YRE), and Pearl (PRE), which cover different climate zones. While δ<sup>30</sup>Si<sub>Si(OH)4</sub> behaved conservatively in the YRE and PRE supporting a dominant control by water mass mixing, significantly increased δ<sup>30</sup>Si<sub>Si(OH)4</sub> signatures due to diatom utilization of Si(OH)<sub>4</sub> were observed in the ARE and reflected a Si isotopic enrichment factor <sup>30</sup>ε of −1.0 ± 0.4‰ (Rayleigh model) or −1.6 ± 0.4‰ (steady state model). In addition, seasonal variability of Si isotope behavior in the YRE was observed by comparison to previous work and most likely resulted from changes in water residence time, temperature, and light level. Based on the <sup>30</sup>ε value obtained for the ARE, we estimate that the global average δ<sup>30</sup>Si<sub>Si(OH)4</sub> entering the ocean is 0.2–0.3‰ higher than that of the rivers due to Si retention in estuaries. This systematic modification of riverine Si isotopic compositions during estuarine mixing, as well as the seasonality of Si isotope dynamics in single estuaries, needs to be taken into account for better constraining the role of large river estuaries in the oceanic Si cycle.</p>}},
  author       = {{Zhang, Zhouling and Cao, Zhimian and Grasse, Patricia and Dai, Minhan and Gao, Lei and Kuhnert, Henning and Gledhill, Martha and Chiessi, Cristiano M. and Doering, Kristin and Frank, Martin}},
  issn         = {{0016-7037}},
  keywords     = {{Biological fractionation; Conservative mixing; Large river estuaries; Riverine Si input; Stable Si isotopes}},
  language     = {{eng}},
  month        = {{03}},
  pages        = {{367--382}},
  publisher    = {{Elsevier}},
  series       = {{Geochimica et Cosmochimica Acta}},
  title        = {{Dissolved silicon isotope dynamics in large river estuaries}},
  url          = {{http://dx.doi.org/10.1016/j.gca.2020.01.028}},
  doi          = {{10.1016/j.gca.2020.01.028}},
  volume       = {{273}},
  year         = {{2020}},
}