16 Nov 2023
 | 16 Nov 2023
Status: this preprint is open for discussion.

Chaetoceros resting spores record low diatom-bound nitrogen isotope values: Evidence from laboratory culture and marine sediment

Isabel A. Dove, Ian W. Bishop, Xavier Crosta, Natascha Riedinger, R. Patrick Kelly, and Rebecca S. Robinson

Abstract. The nitrogen isotopic composition of diatom frustule-bound organic matter (δ15NDB) is often used to study changes in high latitude biological pump efficiency across glacial-interglacial cycles, but the proxy may be biased by species-specific effects. The genus Chaetoceros is of particular interest because of its abundance throughout ocean basins, its shifting biogeography during glacial periods, and many species’ ability to form heavily silicified resting spores. Here we investigate how Chaetoceros resting spores (CRS) record surface nitrate conditions in their nitrogen isotopic composition using both laboratory culture experiments and assemblage-specific sedimentary δ15NDB measurements. We find that CRS record δ15NDB values 7.0 ± 2.6 ‰ lower than vegetative Chaetoceros in culture and 5.6 ± 1.9 ‰ lower than non-CRS diatoms in sediment. Low values are attributed to assimilation of isotopically light ammonium, heavy silicification, and internal fractionation during sporulation. Despite the large δ15NDB difference observed in CRS versus non-CRS diatoms, increased CRS relative abundance in open ocean glacial sediments does not significantly bias δ15NDB records due to the spores’ small size.

Isabel A. Dove et al.

Status: open (until 28 Dec 2023)

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Isabel A. Dove et al.

Data sets

Dissolved nutrients, cell counts, and nitrogen isotope measurements from Chaetoceros socialis culture experiments I. Dove

Sediment chemistry of ODP Site 1098 I. Dove

ODP Site 1098 deglacial diatom assemblage I. Dove

Isabel A. Dove et al.


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Short summary
The diatom-bound nitrogen isotope proxy is used to study how efficiently diatoms in the Southern Ocean help to remove CO2 from the atmosphere, but may be biased by different diatom species. We examine a specific type of diatom, Chaetoceros resting spores (CRS), commonly preserved in Southern Ocean sediments. We find that CRS record surprisingly low δ15NDB values compared to other diatoms, yet changes in their relative abundance over time does not significantly bias previously published records.