Dissolved silicon isotope dynamics in large river estuaries

Author(s)

Zhang, Zhouling ^{[1, 2]} ; Cao, Zhimian ^{[1, 2]} ; Grasse, Patricia ^[3] ; Dai, Minhan ^{[1, 2]} ; Gao, Lei ^[4] ; Kuhnert, Henning ^[5] ; Gledhill, Martha ^[3] ; Chiessi, Cristiano M. ^[6] ; Doering, Kristin ^{[3, 7]} ; Frank, Martin ^[3]

Affiliation

^[1] Xiamen Univ, State Key Lab Marine Environm Sci, Xiamen 361102 - Peoples R China

^[2] Xiamen Univ, Coll Ocean & Earth Sci, Xiamen 361102 - Peoples R China

^[3] GEOMAR Helmholtz Ctr Ocean Res Kiel, D-24148 Kiel - Germany

^[4] East China Normal Univ, State Key Lab Estuarine & Coastal Res, Shanghai 200062 - Peoples R China

^[5] Univ Bremen, MARUM Ctr Marine Environm Sci, D-28359 Bremen - Germany

^[6] Univ Sao Paulo, Sch Arts Sci & Humanities, BR-03828000 Sao Paulo - Brazil

^[7] Dalhousie Univ, Dept Oceanog, Halifax, NS B3H 4R2 - Canada

• Document type: Journal article
• Source: GEOCHIMICA ET COSMOCHIMICA ACTA; v. 273, p. 367-382, MAR 15 2020.
• Web of Science Citations: 0

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 (delta Si-30(Si(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 delta Si-30(Si(OH)4) behaved conservatively in the YRE and PRE supporting a dominant control by water mass mixing, significantly increased delta Si-30(Si(OH)4) signatures due to diatom utilization of Si(OH) 4 were observed in the ARE and reflected a Si isotopic enrichment factor (30)epsilon of -1.0 +/- 0.4 parts per thousand- (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 30e value obtained for the ARE, we estimate that the global average delta Si-30(Si(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. (C) 2020 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 12/17517-3 - Response of the Western Atlantic Ocean to changes in the Atlantic meridional overturning circulation: from millennial to seasonal variability
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Program on Global Climate Change - Young Investigators