Investigating Changes in Single Shell Trace Element Chemistry of Neogloboquadrina dutertrei with Increasing Water Depth Using Sediment Trap Samples from the Panama Basin

The trace element to calcium (TE/Ca) ratios of foraminiferal calcite are widely applied in paleoceanographic reconstructions. Recent studies have documented the formation of carbonate overgrowths (Gibson et al., 2016) and manganese adsorption (Davis et al., 2020) during vertical transport through the water column, demonstrating that foraminifera TE/Ca ratios can be altered prior to deposition on the seafloor. Understanding how different shell regions are impacted has ramifications for interpreting individual foraminifera analyses (IFA) and could further elucidate mechanisms for shell alteration in the water column. Here we investigate changes in single shell trace element chemistry and crusting with depth in specimens obtained from two of the four cups (01 and 04) in the sediment trap time series in the Panama Basin. Individuals of the non-spinose species Neogloboquadrina dutertrei were collected from 3 sediment traps that span a depth gradient. The shallow trap (890m) is well above the regional lysocline, while the mid-depth trap (2590m) is near and the deep trap (3560m) is below the lysocline. Individual shells were analyzed via laser ablation ICP-MS to obtain element profiles through the shell and both individual chamber and whole shell average TE/Ca ratios (B/Ca, Mg/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca). Specimens were subsequently imaged on an SEM to quantify the degree of crusting. Several specimens were also analyzed on a MicroCT scanner to obtain a 3D image of the shell wall, including inner chamber calcite, and to calculate shell density. We find similar TE/Ca ratios between the shallow and mid-depth traps, with the exception of B/Ca, which is statistically higher in the mid depth trap (p = 0.01). There are significant differences (t-test, p-value < 0.05) in the Zn/Ca ratios between the mid-depth and deep sediment traps and in the B/Ca, Zn/Ca and Sr/Ca ratios between the shallow and deep traps. Results demonstrate that water column processes, likely linked to changes in carbonate saturation state, alter these elements prior to deposition on the seafloor. Individual chamber and intrashell TE/Ca variability will also be explored to evaluate whether calcite type or density impacts the TE/Ca alteration experienced during export.