Preprints
https://doi.org/10.5194/bg-2021-21
https://doi.org/10.5194/bg-2021-21

  04 Feb 2021

04 Feb 2021

Review status: this preprint is currently under review for the journal BG.

Growth rate rather than temperature affects the B / Ca ratio in the calcareous red alga Lithothamnion corallioides

Giulia Piazza1, Valentina A. Bracchi1, Antonio Langone2, Agostino N. Meroni3, and Daniela Basso1 Giulia Piazza et al.
  • 1Department of Earth and Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza 4, 20126 Milano, Italy
  • 2CNR – Institute of Geosciences and Earth Resources, Via Ferrata 1, 27100 Pavia, Italy
  • 3Department of Civil and Environmental Engineering, Politecnico of Milan, Piazza Leonardo da Vinci 32, 20133 Milano, Italy

Abstract. The B / Ca ratio in calcareous marine species is informative of past seawater CO32− concentrations, but scarce data exist on B / Ca in coralline algae (CA). Recent studies suggest influences of temperature and growth rates on B / Ca, the effect of which could be critical for the reconstructions of surface ocean pH and atmospheric pCO2. In this paper, we present the first LA-ICP-MS analyses of Mg, Sr, Li and B in the CA Lithothamnion corallioides collected from different geographic settings and depths across the Mediterranean Sea and in the Atlantic Ocean. We produced the first data on temperature proxies (Mg, Li and Sr / Ca) and B / Ca in a CA species grown in different Basins (the Mediterranean Sea and the Atlantic Ocean), from shallow to deep waters (12 m, 40 m, 45 m and 66 m depth). We tested the B / Ca correlation with temperature proxies and growth rates, in order to evaluate their possible effect on B incorporation. Our results showed a growth rate influence on B / Ca, especially in the deepest sample (Pontian Isl., Italy; 66 m) and in the shallowest sample (Morlaix, Atlantic coast of France; 12 m), where the growth rates were respectively 0.11 mm/yr and 0.13 mm/yr and the B / Ca was respectively 462.8 ± 49.2 μmol/mol and 726.9 ± 102.8 μmol/mol. A positive correlation between B / Ca and the temperature proxies was found only in Morlaix, where the seasonal temperature variation (ΔT) was the highest (8.90 °C). These pieces of evidence suggest that growth rates, triggered by the different ΔT and light availability across depth, affect the B incorporation in L. corallioides.

Giulia Piazza et al.

Status: open (until 24 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-21', Anonymous Referee #1, 24 Feb 2021 reply
  • RC2: 'Comment on bg-2021-21', Anonymous Referee #2, 02 Mar 2021 reply
  • RC3: 'Comment on bg-2021-21', Anonymous Referee #3, 04 Mar 2021 reply

Giulia Piazza et al.

Giulia Piazza et al.

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Short summary
The coralline alga Lithothamnion corallioides is widely distributed in the Mediterranean Sea and in the NE Atlantic Ocean, where it constitutes rhodolith beds, diversity-rich ecosystems on the seabed. The boron incorporated in the calcified thallus of coralline algae (B / Ca) can be used to trace past changes in the seawater carbonate and pH. This paper suggests a non-negligible effect of algal growth rate on B / Ca, suggesting caution in adopting this proxy for paleoenvironmental reconstructions.
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