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Impact of human disturbance on the biogeochemical silicon cycle in a coastal sea revealed by silicon isotopes

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doi: 10.1002/lno.11320
Authors:Zhang Zhouling; Sun, Xiaole; Dai Minhan; Cao Zhimian; Fontorbe, Guillaume; Conley, Daniel J.
Author Affiliations:Primary:
Xiamen University, State Key Laboratory of Marine Environmental Science, Xiamen, China
Lund University, Sweden
Stockholm University, Sweden
Volume Title:Limnology and Oceanography
Source:Limnology and Oceanography, 65(3), p.515-528. Publisher: American Society of Limnology and Oceanography, Ann Arbor, MI, United States. ISSN: 0024-3590
Publication Date:2020
Note:In English. 65 refs.; illus., incl. 1 table, sketch map
Summary:Biogeochemical silicon (Si) cycling in coastal systems is highly influenced by anthropogenic perturbations in recent decades. Here, we present a systematic study on the distribution of stable Si isotopes of dissolved silicate (δ30SiDSi) in a highly eutrophic coastal system, the Baltic Sea. Besides the well-known processes, diatom production and dissolution regulating δ30SiDSi values in the water column, we combined field data with a box model to examine the role of human disturbances on Si cycling in the Baltic Sea. Results reveal that (1) damming led to increased δ30SiDSi values in water but had little impacts on their vertical distribution; (2) decrease in saltwater inflow due to enhanced thermal stratification had negligible impacts on the δ30SiDSi distribution. An atypical vertical distribution of δ30SiDSi with higher values in deep water (1.57-1.95 ppm) relative to those in surface water (1.24-1.68 ppm) was observed in the central basin. Model results suggest the role of enhanced biogenic silica (BSi) deposition and subsequently regenerated dissolved silicate (DSi) flux from sediments. Specifically, eutrophication enhances diatom production, resulting in elevated exports of highly fractionated BSi to deep water and sediments. In situ sedimentary geochemical processes, such as authigenic clay formation, further fractionate Si isotopes and increase pore-water δ30SiDSi values, which then leads to pore-water DSi flux carrying higher δ30SiDSi compositions into deep water. Our findings provide new quantitative information on how the isotope-based Si cycle responds to human perturbations in coastal seas and shed lights on shifts of Si export to open ocean. Abstract Copyright (2019), Association for the Sciences of Limnology and Oceanography.
Subjects:Biochemistry; Brackish water; Chemical composition; Coastal environment; Human activity; Isotope ratios; Isotopes; Oceanography; Si-30/Si-28; Silicon; Stable isotopes; Atlantic Ocean; Baltic Sea; Gotland Basin; North Atlantic; Silicon cycle
Record ID:875049-5
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom
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