Ultradian rhythms in shell composition of photosymbiotic and non-photosymbiotic mollusks

• Published in: Biogeosciences Vol. 20; no. 14; pp. 3027 - 3052
• Main Authors: de Winter, Niels J, Killam, Daniel, Fröhlich, Lukas, de Nooijer, Lennart, Boer, Wim, Schöne, Bernd R, Thébault, Julien, Reichart, Gert-Jan
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 28-07-2023; European Geosciences Union; Copernicus Publications
• Subjects: Ablation; Annual variations; Archives & records; Armor; Barium; Biological activity; Calcium; Chemical composition; Chemistry; Circadian rhythm; Clams; Climate change; Climatology; Daily; Diurnal; Ecology, environment; Environmental conditions; Laser ablation; Life Sciences; Magnesium; Manganese; Marine molluscs; Mass spectrometry; Mass spectroscopy; Mean; Mollusks; Periodic variations; Periodicity; Shells; Spectral analysis; Spectrum analysis; Stable isotopes; Statistical analysis; Strontium; Tidal rhythm; Trace elements; Ultradian rhythms; Weather patterns; Bay of Brest; STABLE-ISOTOPES; CERASTODERMA-EDULE; ARAGONITIC BIVALVE SHELLS; RESOLUTION TRACE-ELEMENT; TRIDACNA-GIGAS BIVALVES; GROWTH-RATESICP-MS; ARCTICA-ISLANDICA; CLIMATE VARIABILITY; GIANT CLAM
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-20-3027-2023

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 analysis with
improved sampling resolution now allows in situ determination of the composition of mollusk shell volumes precipitated at daily to sub-daily time intervals. Here, we discuss hourly resolved Mg / Ca, Mn / Ca, Sr / Ca, and Ba / Ca profiles
measured by laser ablation inductively coupled plasma – mass spectrometry (ICP-MS) through shells of the photosymbiotic giant clams (Tridacna maxima, T. squamosa, and T. 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 weak but statistically significant expressions of these periods and 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−1
(∼ 10 % of mean value) in Mg / Ca and Sr / Ca, while ultradian Mn / Ca and Ba / Ca cyclicity has a
median amplitude of less than 2 µmol mol−1 mol mol−1 (∼ 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 among the strongest diurnal cyclicity. Daily cycles in the trace element composition of giant clams are therefore unlikely to be driven by variations in direct insolation but rather reflect an inherent
biological rhythmic process affecting element incorporation. Finally, the
large amount of short-term trace element variability unexplained by tidal
and daily rhythms highlights the dominance of aperiodic processes in mollusk
physiology and/or environmental conditions over shell composition at the
sub-daily scale. Future studies should aim to investigate whether this
remaining variability in shell chemistry reliably records weather patterns
or circulation changes in the animals' environment.