the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Ultradian rhythms in shell composition of photosymbiotic and non-photosymbiotic mollusks
Daniel Killam
Lukas Fröhlich
Lennart Nooijer
Wim Boer
Bernd R. Schöne
Julien Thébault
Gert-Jan Reichart
Abstract. The chemical composition of mollusk shells is a useful tool in (paleo)climatology since it captures inter- and intra-annual variability in environmental conditions. Trace element and stable isotope analyses with improved sampling resolution now enable the use of mollusk shells for paleoenvironmental reconstructions at a daily to sub-daily resolution. Here, we discuss hourly resolved Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca profiles measured by laser ablation ICP-MS through shells of photosymbiotic giant clams (Tridacna maxima, Tridacna squamosa and Tridacna squamosina) and the non-photosymbiotic scallop Pecten maximus. Precise sclerochronological age models and spectral analysis allowed us to extract daily and tidal rhythms in the trace element composition of these shells. We find significant expression of these periodicities but conclude that this cyclicity explains less than 10 % of the sub-annual variance in trace element profiles. Tidal and diurnal rhythms explain variability of at most 0.2 mmol/mol (~10 % of mean value) in Mg/Ca and Sr/Ca, while Mn/Ca and Ba/Ca cyclicity has a median amplitude of less than 2 µmol/mol (~40 % and 80 % of the mean of Mn/Ca and Ba/Ca, respectively). Daily periodicity in Sr/Ca and Ba/Ca is stronger in Tridacna than in Pecten, with Pecten showing stronger tidal periodicity. One T. squamosa specimen which grew under a sunshade exhibits some of the strongest diurnal cyclicity. Daily cycles in trace element composition of giant clams are therefore unlikely to be driven by variations in direct insolation itself but reflect an inherent biological rhythmic process affecting element incorporation. Finally, the large amount of trace element variability unexplained by periodic variability highlights the dominance of aperiodic processes in mollusk physiology and/or environmental conditions on shell composition at the sub-daily scale. Future studies should aim to investigate whether part of this aperiodic variability in shell chemistry reliably records weather patterns or circulation changes in the paleoenvironment.
Niels J. de Winter et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-576', Anonymous Referee #1, 29 Oct 2022
de Winter et al. present a comprehensive dataset on trace elements in scallops and giant clams. The data are robust and they do a good job presenting them. My comments are minor and mostly deal with adding to the discussion and referencing previous works.
I recommend to publish with minor changes.
Abstract
Reads too positive – should be toned down.
E.g.,:
“now enable the use of mollusk shells for paleoenvironmental reconstructions at a daily to sub-daily resolution”
“We find significant expression of these periodicities”
L518-519 – be more explicit and less colloquial. “There is some discussion”? In the published literature? Maybe say previous studies… Then “This study’s” – are you referring to the citations in the previous sentence or are you referring to the work you present here? Also, “the same year in the same environment” as what?
L521 “arguing against a simple temperature dependence for Mg/Ca” – maybe say agreeing with previous studies
L523 – Lorrain et al. 2005 also found this – state that here
L536 Gillikin et al. 2006 (doi:10.1016/j.gca.2005.09.015) discuss separating the background Ba/Ca from the peaks. If these shells all grew in the same salinity they should all have similar background values. Do you see this? I think this should be commented on here.
L541 – the subheader here is wrong, this section is about scallops
L599 – should discuss Carre et al 2006 (already cited) and Gillikin et al. 2005 (doi:10.1029/2004GC000874) here.
Section 4.4.2 – I don’t think this section clearly shows how your data contribute to this idea. It’s mostly a discussion of previous studies. A sentence or two blending your results into this would bolster this discussion.
Many citations are missing journal names (e.g., L895, L903, L919, L924, L927, L929, L936 and many others…)
Citation: https://doi.org/10.5194/egusphere-2022-576-RC1 -
AC1: 'Reply on RC1', Niels de Winter, 09 Nov 2022
Dear reader,
We would like to thank Reviewer 1 for the positive review of our manuscript, and for the helpful comments that will allow us to improve it. In the file attached, we reply to the review comments point-by-point and explain how we plan to make changes in the manuscript following the reviewer’s suggestions.
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AC1: 'Reply on RC1', Niels de Winter, 09 Nov 2022
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RC2: 'Comment on egusphere-2022-576', Anonymous Referee #2, 02 Dec 2022
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AC2: 'Reply on RC2', Niels de Winter, 22 Dec 2022
Dear editor,
We appreciate the time and effort spent by Reviewer 2 to comment on our manuscript. We are glad to read that the reviewer likes the design of our study overall and thinks the topic is worthwhile. Their main concern relates to the effective sampling resolution of our LAICPMS method and our ability to capture daily variability in the shells. Below, we provide a rebuttal to this major point below before listing our point-by-point replies to the other questions raised by the reviewer. We hope the changes we suggest will make our manuscript acceptable for revision and subsequent publication in Biogeosciences.
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AC2: 'Reply on RC2', Niels de Winter, 22 Dec 2022
Niels J. de Winter et al.
Data sets
TE_circadian Niels J. de Winter https://github.com/nielsjdewinter/TE_circadian
Supplementary information for: "Ultradian rhythms in shell compositions of photosymbiotic and non-photosymbiotic mollusks" Niels J. de Winter, Daniel Killam, Lukas Fröhlich, Lennart de Nooijer, Wim Boer, Bernd R. Schöne, Julien Thébault, Gert-Jan Reichart https://doi.org/10.5281/zenodo.6602894
Niels J. de Winter et al.
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