Impact of Preservative Medium and Oxidative Cleaning on the Trace Element Geochemistry and Stable Isotope Composition of Modern Foraminifera

Abstract Collection of modern foraminifera for paleoproxy development studies often require samples to be preserved. Shells are then typically cleaned prior to geochemical analysis. Preservation and cleaning reagents could impact the shell trace element (TE) or stable isotope composition via contamination or post‐preservation calcite alteration. For example, the Na/Ca composition of the calcite could be impacted by both the borax (Na 2 B 4 O 5 (OH) 4 · 8H 2 O)‐buffered formalin preservative and the sodium hydroxide (NaOH) used in cleaning. Here we investigate the impact of preservative medium (borax‐buffered formalin and ethanol) and oxidative cleaning on shell TE/Ca ratios (Mg, Na, Sr, Ba, Mn, Zn) and δ 13 C and δ 18 O composition of modern planktic foraminifera collected via plankton tow. Results show that δ 13 C, δ 18 O, and all TE/Ca ratios, except for Zn/Ca, are unaffected by preservation medium when compared to a control group. Shells preserved in ethanol exhibit highly elevated Zn/Ca ratios compared to the borax‐buffered formalin and control specimens. Similarly, the oxidative cleaning step had no impact on TE/Ca ratios, except for Zn/Ca, which decreases when additional rinses are performed after the oxidative cleaning step. These impacts on foraminiferal Zn/Ca ratios may be an important contributor to the difficulty in constraining the dominant environmental control on Zn incorporation in foraminifera and will need to be considered in any future paleoproxy development, paleoceanographic, or biomonitoring studies investigating Zn/Ca. Results herein provide promising support for the usage and comparison of most geochemical data collected from modern foraminifera that were exposed to different preservatives or underwent an oxidative cleaning procedure.