Effects of pre-treatment on ostracod valve chemistry

The stable-isotope and trace-element analysis of ostracod calcite are commonly used in palaeoenvironmental reconstruction. We tested the effects on shell composition of a number of methods for the pre-treatment of ostracod valves, including roasting in a vacuum; plasma ashing; and soaking in reagents including hydrogen peroxide, sodium hypochlorite, hydroxylamine hydrochloride solution and sodium dithionite complexing reagent. We found large differences in the geochemical effects of these methods and showed that all have the potential to alter the trace element and stable isotope composition of ostracod valves. We recommend that valves only be cleaned manually, with fine brushes, needles and deionised water whenever possible. However, we recognise that there will be occasions where manual cleaning will be insufficient to remove inorganic or organic contamination. In such cases, we recommend hydrogen peroxide and plasma ashing as good methods for oxygen isotope analysis, if no other analyses are to be performed. For carbon isotope analysis, only plasma ashing should be used. Hydroxylamine hydrochloride is a suitable method for the removal of aluminosilicate material, and sodium hypochlorite is a suitably non-invasive method for the removal of organic material, if subsequent trace element analysis is to be carried out.