A NOVEL APPROACH TO DETERMINING FORAMINIFERA TEST VOLUMES

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 geochemical analysis and presence/absence data, but foraminiferal morphologies are also sensitive to variations in available oxygen. Foraminifera test size (volume and surface area) 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 scanning, or quicker but less accurate geometric approximations that often fail to accurately correlate with the dimensions of the foraminifera they are measuring.

A novel method for determining test volume has been developed to allow for quick and accurate results. This process utilizes high-resolution microscopic imaging to produce a focus-stacked image of the foraminifera test. The image is then used to produce a 3D topographic mesh of the test. This topographic mesh is then processed and imported into a commercially available CAD software program. Using CAD solid-body simulation, the volume and surface area of the test is algorithmically calculated.

This new topographic method has been performed on a small set of C. wuellerstorfi and U. peregrina samples. These species were chosen based on their ease of acquisition, comparatively different test geometries, and paleoceanographic significance. Results compared with the values derived from geometric equations showed the expected correlation with the equation-based volumes. The topographic method’s results trended higher than the values from equations that under-estimate the test volume and lower than values from over-estimating equations.

Data from the topographic method, geometric approximation, and micro-CT scanned volumes on a larger set of samples will allow for the comparison of all three methods and assess the accuracy of each. It is expected that results will show that the new method produces a result that is much closer in value to the micro-CT method than the use of geometric equations. If the expected results hold true, the novel topographic method will provide a much faster and cost-efficient method for determining micro-fossil volumes.