1. Calibrating the triple oxygen isotope signature of cultured diatoms.
- Author
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Liljestrand, Frasier L., Hania, Anxhela, Giordano, Mario, and Johnston, David T.
- Subjects
DIATOMS ,DIATOM frustules ,OXYGEN isotopes ,CENOZOIC Era ,ORGANIC compounds - Abstract
The 18O/16O of precipitated silica in natural environments is posited to record the temperature of the ambient environment. Measurements of 17O/16O in silica (SiO2), when paired with 18O/16O, provide an opportunity to further constrain the environmental conditions at the time of mineral precipitation and ripening. On Cenozoic timescales, siliceous frustule precipitation by diatoms has served as the primary sink of silica from the ocean. Frustule precipitation is a biologically catalyzed process from an ocean undersaturated in SiO2. Here, we measure the 17O/16O and 18O/16O in diatom frustules from semicontinuous cultures with two different diatom species and across a range of growth rates and temperatures. To further enable these measurements, we developed a laser fluorination method to reproducibly measure the triple oxygen isotope composition of silica frustules. While the δ13C of the organic matter scaled predictably with growth rate, neither the δ18O or Δ′17O of the frustule silica varied significantly with respect to variations in growth rate or species. Temperature, however, does carry a control on the product δ18O composition. Conversely, the measured Δ′17O compositions were systematically negative with respect to the corresponding theoretical equilibrium isotope prediction, consistent with other empirical work on the SiO2 system and only weakly temperature‐dependent. This isotopic offset may be caused by the silica concentrating mechanisms diatoms use to precipitate their frustules. These results are consistent with literature arguments regarding the utility of diatom δ18O in reconstructing temperature, but suggest that Δ′17O may not be a suitable temperature proxy for diatomaceous sediment. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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