Diapositive 1 - de l'Université libre de Bruxelles

Chapitre IIIalready proposed by Vander Putten et al (2000) to account for seasonal variations in theMg content of Mytilus edulis calcite shell layer. Acidic organic macromolecules stabilizein vitro the transient ACC phase (Raz et al 2000) and possibly play an important role inthe hydration of this phase, allowing an easier incorporation of the Mg ion, which has arelatively large dehydration barrier (Cheng et al 2007). Furthermore, Robach et al (2006)demonstrated that higher Mg concentrations in the sea urchin tooth were linked to matrixmolecules richer in aspartic acid. Thus, one may hypothesize that more acid matrixmolecules will, in vivo, further stabilize the transient ACC phase, allowing for a higherincorporation of Mg.Using Ries’ (2004) algorithms we reconstructed seawater Mg/Ca ratio and the errorinduced by the salinity effect on the calcite Mg/Ca ratio. This induced an error in deducedseawater Mg/Ca ratio between 2% and 5% at a difference of 1 psu and between 16% and46% for a difference of 10 psu (Figure 26), according to the seawater Mg/Ca ratio. Thehighest error occurs for the lowest seawater Mg/Ca ratio of 1.29, i.e., values inferred for apart of the Phanerozoic oceans (see e.g., Dickson 2002).This result emphasizes the need to consider the salinity effect, with the temperature effect,when reconstructing long-term changes (Δt > 1 m.y.) in the seawater Mg/Ca ratio.Figure 26: Impact (%) of the salinity effect on the seawater Mg/Ca ratio reconstruction based on Ries’(2004) algorithms (Mg/Ca skeleton =(0.0471×Mg/Ca SW 0.668 )71