Do different extraction techniques impact planktic foraminiferal assemblages? An early Eocene case study

Abstract

Abstract Here we report and compare results on planktic foraminiferal assemblages extracted with five disaggregation techniques: acetic acid, H2O2 at 10% and 25% concentration, neosteramina, and liquid N2. The aim is to estimate whether these laboratory procedures can affect the pristine assemblages or add secondary dissolution effects. We apply these five methods on three samples with different carbonate content from the early Eocene Tethyan Terche section (northeast Italy). For each method we assess: (1) the treatment effectiveness in relation to time required to successfully extract planktic foraminiferal tests and preservation; (2) the degree of dissolution through the analyses of three well-known dissolution proxies including the fragmentation index, the planktic benthic ratio and the weight percent coarse fraction; (3) changes in planktic foraminiferal assemblages through genera and species absolute abundances and the evaluation of multiple species diversity indices. Our data demonstrate that acetic acid and neosteramina treatments are the most effective methods as they represent the only ones capable in disaggregating the samples with higher CaCO3 content whereas liquid N2 revealed to be the best treatment to adopt for samples with low CaCO3 content. The best-preserved foraminiferal specimens derive from the acetic acid and neosteramina treatments. Nonetheless, the acetic acid along with H2O2 treatments, at both concentrations, can impact planktic foraminiferal assemblages affecting the diversity or species abundances. Dissolution of planktic foraminifera shows a complex relationship with the initial carbonate content (CaCO3%) of the samples and with the different dissolution susceptibility of the species that can differ according to the laboratory procedures.