A study of sclerochronology by laser ablation ICP-MS

Sclerochronology is to shells what dendrochronology is to trees, i.e., growth structures within some shells (in this case the bivalve mollusc Arctica islandica L., the Ocean Quahoc) resemble, in form and content, those growth structures in trees, which grow with an annual periodicity. By utilising laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), allied with stable isotope analysis to sample the growth structures within shells, environmental conditions (e.g., ambient temperature, salinity, seasonality and productivity) prevalent at the time of shell genesis may be ascertained. A limiting factor in the retrieval of any data from biogenic carbonates such as these is the size of the repeated growth structures from which to extract information. In the case of Arctica, these can be as low as tens of µm. Micro-drilling techniques, such as those commonly used in isotope analyses, are constrained by the size of the drill bit used to collect the sample. LA-ICP-MS, with its ultra-high spatial resolution (10–20 µm ablation pits) and precision, delivers highly constrained analysis allowing accurate multi-element sampling of seasonal growth bands within shells. It may be feasible to use the elements strontium, magnesium and barium as records of inter-annual environmental conditions, thus removing the need to carry out stable isotope analyses in some instances, particularly where the size of the material to be sampled demands the high resolution of LA-ICP-MS.