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The Missing Silica Sink: Revisiting the Marine Sedimentary Si Cycle Using Cosmogenic 32Si
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| Zeitschriftentitel: | Global Biogeochemical Cycles |
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| Personen und Körperschaften: | , , |
| In: | Global Biogeochemical Cycles, 31, 2017, 10, S. 1559-1578 |
| Format: | E-Article |
| Sprache: | Englisch |
| veröffentlicht: |
American Geophysical Union (AGU)
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| Schlagwörter: |
| Zusammenfassung: | <jats:title>Abstract</jats:title><jats:p>Burial of biogenic silica (bSi<jats:sub>total</jats:sub>) in high sedimentation rate continental margins remains highly uncertain. Cosmogenic <jats:sup>32</jats:sup>Si (t<jats:sub>1/2</jats:sub>~140 years) can be used to trace the fates of bSi<jats:sub>total</jats:sub> postdeposition, including as opal (bSi<jats:sub>opal</jats:sub>) and diagenetically altered opal (bSi<jats:sub>altered</jats:sub>), the latter dominantly authigenic clay (bSi<jats:sub>clay</jats:sub>). To determine the magnitude and form of bSi<jats:sub>total</jats:sub> storage in coastal sediments, conventional operational leaches targeting bSi<jats:sub>opal</jats:sub> and bSi<jats:sub>altered</jats:sub> (including bSi<jats:sub>clay</jats:sub>) were modified for large‐scale samples necessary for measurement of <jats:sup>32</jats:sup>Si. The <jats:sup>32</jats:sup>Si activity was used to estimate total biogenic silica burial (bSi<jats:sub>total</jats:sub> = bSi<jats:sub>opal</jats:sub> + bSi<jats:sub>altered</jats:sub>) in several depositional settings: Gulf of Papua, Gulf of Mexico, Long Island Sound, and in the previously studied Amazon‐Guianas deltaic system. In subtropical and temperate regions, <jats:sup>32</jats:sup>Si was detected in both traditional biogenic silica leaches (bSi<jats:sub>opal</jats:sub>) and residual authigenic clays. Traditional bSi<jats:sub>opal</jats:sub> and modified operational leaches designed to target the most reactive authigenic silicates (~bSi<jats:sub>altered</jats:sub>) consistently underestimate authigenic clay formation (bSi<jats:sub>clay</jats:sub>) and thus the magnitude of bSi<jats:sub>total</jats:sub> burial in temperate coastal zones and subtropical deltas by 2–4‐fold. In tropical deltas, <jats:sup>32</jats:sup>Si activities in the residual fraction after removal of bSi<jats:sub>opal</jats:sub> demonstrate rapid and almost complete alteration of initial bSi<jats:sub>opal</jats:sub> to new forms, most likely bSi<jats:sub>clay</jats:sub>. Globally, 4.5–4.9 Tmol/yr Si may be trapped in marine nearshore deposits as rapidly formed clay (bSi<jats:sub>clay</jats:sub>), 100% of the “missing silica sink” in the marine silica budget.</jats:p> |
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| Umfang: | 1559-1578 |
| ISSN: |
0886-6236
1944-9224 |
| DOI: | 10.1002/2017gb005746 |