DOI 10.1016/j.chemgeo.2023.121396 Insights into past marine carbon cycling and water mass properties can be obtained by means of geochemical proxies calibrated through controlled laboratory experiments with accurate seawater carbonate system (C-system) manipulations. Here, we explored the use of strontium/calcium ratio (Sr/Ca) of the calcite shells of benthic foraminifera as a potential seawater C-system proxy through a controlled growth experiment with two deep-sea species (Bulimina marginata and Cassidulina laevigata) and one intertidal species (Ammonia T6). To this aim, we used two experimental set-ups to decouple as much as possible the individual components of the carbonate system, i.e., changing pH at constant dissolved inorganic carbon (DIC) and changing DIC at constant pH. Four climatic chambers were used with different controlled concentrations of atmospheric pCO2 (180 ppm, 410 ppm, 1000 ppm, 1500 ppm). Our results demonstrated that pH did not influence the survival and growth of the three species. However, low DIC conditions (879 μmol kg−1) negatively affected B. marginata and C. laevigata through reduced growth, whereas no effect was observed for Ammonia T6. Our results also showed that Sr/Ca was positively correlated with total Alkalinity (TA), DIC and bicarbonate ion concentration ([HCO3−]) for Ammonia T6 and B. marginata; i.e., DIC and/or [HCO3−] were the main controlling factors. For these two species, the regression models were coherent with published data (existing so far only for Ammonia T6) and showed overall similar slopes but different intercepts, implying species-specific effects. Furthermore, the Sr/Ca - C-system relationship was not impacted by ontogenetic trends between chamber stages, which is a considerable advantage for paleo-applications. This applied particularly to Ammonia T6 that calcified many chambers compared to the two other species. However, no correlation with any of the C-system parameters was observed for Sr/Ca in C. laevigata. This might imply either a strong species-specific effect and/or a low tolerance to laboratory conditions leading to a physiological stress, thereby impacting the Sr incorporation into the calcite lattice of C. laevigata.
Carbonate system, Culture experiment, Sr/ca, Benthic foraminifera, Ocean acidification, Biomineralisation
| File | Pages | Size | Access | |
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Author's final draft | 50 | 3 Mo | ||
Supplementary material S1. Images of the three cultured species under natural and epifluorescent lights. Asterisks indicate the newly formed chambers that appear non-fluorescent. | - | 1 Mo | ||
Supplementary material S2. Illustrations of the Ecolab structure and the experimental set-up. a) Aerial view of the Ecolab parc (© CEREEP Ecotron, Ile de France); b) Ecolab structure; c) Illustrations | - | 2 Mo | ||
Supplementary material S3. Graphics showing the three measured parameters of the C-system during the experiment. | - | 1 Mo | ||
Supplementary material S4. a) Operating parameters of the LA-ICP-MS analyses, b) repeatability, and c) accuracy of standards El/Ca analyses. | - | 5 Mo | ||
Supplementary material S5. SEM pictures of the three studied species in various pseudo-replicates, at the initial state (before experimentation), and at B180, A410 and A1500 conditions. All pictures.. | - | 2 Mo | ||
Supplementary material S6. Box plots showing Sr/Ca (mmol mol−1) measured in foraminiferal calcite as a function of the position of the newly formed chambers in each experimental condition;.... | - | 1 Mo | ||
Supplementary material S7. Plots of DSr values vs [HCO3−] and Mg/Cacc comparing our data of Ammonia T6 with data reported in different culture studies using Ammonia spp. and some planktonic species. | - | 1 Mo | ||
Supplementary material S8. Additional discussion on Sr partition coefficient (DSr). | - | 45 Ko | ||
Supplementary material S9. Foraminiferal Mg/Ca, Zn/Ca and Ba/Ca (mmol mol−1) versus individual C-system parameters for Ammonia T6 and B. marginata. Lines represent linear regressions. | - | 1 Mo | ||
Publisher's official version | 18 | 11 Mo |
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