FORAMINIFERA VOLUMETRICS FROM FOCUS-STACKED MICROSCOPY

Benthic foraminifera have long been used as an indicator for dissolved oxygen availability at and just below the sediment-water interface. This has been done, predominantly, via geochemistry and presence/absence data, but foraminiferal morphologies have also been shown to be sensitive to variations in available oxygen. Foraminifera test size has been inversely correlated with the availability of aqueous oxygen. The study of foraminiferal morphology relies on accurate measurements at small scales, leading to the required use of expensive and time-consuming methodologies, such as micro-CT, or quicker but less accurate geometric approximations that often fail to accurately correlate with the dimensions of the foraminifera they are measuring. A method for determining test volume has been developed to allow for quick and accurate results. This process utilizes high-resolution light microscopy to produce a focus-stacked image of the foraminifera, which is then used to produce a 3D topographic mesh of the test. The volume of this mesh is then determined using commercially available CAD software. A comparison of all three methods has been performed to assess the accuracy of each. Both C. wuellerstorfi and U. peregrina samples were chosen based on their ease of acquisition, comparatively different test geometries, and paleoceanographic significance. This study indicates the new method produces a result that is much closer in value to the micro-CT method than the use of geometric equations. Based on these results, the novel topographic method provides a much faster and cost-efficient method for determining micro-fossil volumes.