Silicon isotopes of deep sea sponges: new insights into biomineralisation and skeletal structure
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Published:2018-11-21
Issue:22
Volume:15
Page:6959-6977
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Cassarino Lucie,Coath Christopher D.,Xavier Joana R.,Hendry Katharine R.
Abstract
Abstract. The silicon isotopic composition (δ30Si) of
deep sea sponges' skeletal element – spicules – reflects the silicic acid
(DSi) concentration of their surrounding water and can be used as natural
archives of bottom water nutrients. In order to reconstruct the past silica
cycle robustly, it is essential to better constrain the mechanisms of
biosilicification, which are not yet well understood. Here, we show that the
apparent isotopic fractionation (δ30Si) during spicule
formation in deep sea sponges from the equatorial Atlantic ranges from
−6.74 ‰ to −1.50 ‰ in relatively low DSi concentrations
(15 to 35 µM). The wide range in isotopic composition highlights
the potential difference in silicification mechanism between the two major
classes, Demospongiae and Hexactinellida. We find the anomalies in the
isotopic fractionation correlate with skeletal morphology, whereby fused
framework structures, characterised by secondary silicification, exhibit
extremely light δ30Si signatures compared with previous
studies. Our results provide insight into the processes involved during
silica deposition and indicate that reliable reconstructions of past DSi can
only be obtained using silicon isotope ratios derived from sponges with
certain spicule types.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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