High resolution distribution of magnesium and strontium and the evaluation of Mg/Ca thermometry in Recent brachiopod shells

Citation

Pérez-Huerta A, Cusack M, Jeffries TE & Williams T (2008) High resolution distribution of magnesium and strontium and the evaluation of Mg/Ca thermometry in Recent brachiopod shells. Chemical Geology, 247 (1-2), pp. 229-241. https://doi.org/10.1016/j.chemgeo.2007.10.014

Abstract
High resolution distribution of magnesium and strontium determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) are presented in this study for Recent brachiopod shells. The concentration of magnesium and strontium decreases in a similar fashion from the outer to inner regions of shells of rhynchonelliform species but remains unaltered in craniid brachiopods. In rhynchonelliform brachiopods with low-magnesium shells, there is a characteristic chemical profile with an abrupt decrease in magnesium concentration from the primary layer towards the secondary layer until it reaches a region in which the values are almost constant. In addition, there is a proportional relationship in magnesium concentration between primary and secondary layers. Both findings demonstrate the biological control in magnesium incorporation in rhynchonelliform brachiopods confirming previously reported findings. Calculated Mg/Ca ratios based on magnesium concentrations within the innermost region of the secondary layer show that rhynchonelliform brachiopods can record seawater temperature. This finding opens up the possibility of using Mg/Ca (palaeo) thermometry even within the context of biological control and the potential application of Mg/Ca ratios as a seawater temperature proxy in fossil brachiopods. © 2007 Elsevier B.V. All rights reserved.

Keywords
LA-ICP-MS; calcite; secondary layer; biological control

Journal
Chemical Geology: Volume 247, Issue 1-2