The effect of chemical pretreatment of sediment upon foraminiferal‐based proxies

Abstract

Paleoceanographic studies routinely combine different foraminiferal proxies (i.e., weight, abundance, trace metal, and stable isotope measurements) into a cohesive narrative. The application of chemical treatment to disaggregate ocean sediments in the most efficient way to isolate the fossils of foraminifera from the other sediment components is dictated by the time available and the material used. Yet few studies have aimed to test both the physical and geochemical effects associated with such practices. In this study, we use samples with different sedimentological characteristics (i.e., varying percentages of CaCO3 and of terrigenous material) to test the impact upon these proxies of three processing methods and a control: (1) no chemicals (contol run); (2) soaking in sodium hexametaphosphate (Calgon®); (3) soaking in hydrogen peroxide; and (4) soaking in a sodium pyrophosphate. The samples were analyzed for faunal abundance, shell weight, stable isotope (δ18O, δ13C), and trace metal (Mg/Ca) geochemistry for four species of planktonic foraminifera (Globigerina bulloides, Globigerinoides ruber, Globorotalia inflata, and Globorotalia menardii). Results show that apart from the Calgon® solution, the values of faunal abundance, shell weight, Mg/Ca, and stable isotopes are similar irrespective of the cleaning treatment utilised and therefore warrant cross‐comparison of results obtained with different preparation techniques. The use of Calgon® in pretreatment shows statistically different values for only foraminiferal shell weight.