High resolution distribution of trace elements in the calcite shell layer of modern mytilus edulis: environmental and biological controls

Mussels of a similar size, originating from the same population, have been grown in the field and the high resolution distribution of Mg, Mn, Sr, Ba and Pb in their calcite shell layer, as determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry, has been compared to temporal variations of environmental parameters. All elements exhibit cyclic variations with an annual periodicity. The Mg, Sr and Pb cycles show great similarity and are characterised by a broad maximum during spring and early summer. These profiles cannot be explained by seasonal variations in the seawater composition. Skeletal Mg covaries reproducibly with temperature during spring but this covariation is abruptly interrupted after the spring phytoplankton bloom. The absence of a constant Mg-temperature relationship over the year hampers the direct use of Mg in M. edulis calcite as a high resolution temperature proxy. The sharp peak that is dominating each skeletal Ba cycle coincides with the annual algal biomass maximum and presumably reflects elevated concentrations of particulate Ba, associated with the spring phytoplankton bloom. Similarly, elevated skeletal Mn concentrations during spring might reflect bloom-induced increases in particulate Mn. Skeletal δ 13C shows a seasonal variation, characterised by a minimum that coincides with the Mn maximum. These δ 13C variations are not in equilibrium with the seasonal δ 13C trend of the seawater dissolved inorganic carbon and presumably reflect fluctuations in the contribution of metabolic carbon to the shell carbonate, corresponding to seasonal variations in the mussel’s respiration rate.