21 Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

Traditional applications of microfossils are central to many studies, while novel approaches (especially geochemistry) utilizing microfossils have expanded recently. This session highlights traditional and innovative microfossil applications in terrestrial and marine environments, including modern analogs.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 303C

Reconstructing Foraminifera Ecology: Application of Compound-Specific Stable Isotope Analysis of Amino Acids to Fossil Foraminifera Tests

Paper number: 21-15
Program: Technical Sessions
Time: 11:40 AM – 11:55 AM

Authors

Abstract

Planktonic foraminifera are widely used in paleoenvironmental reconstructions due to their broad geographic distribution, excellent preservation in the sediment record, and high species diversity. These characteristics make them powerful proxies for past ocean conditions. Paleoceanographic studies must often rely on fossil groups with no modern counterparts, posing challenges for ecological interpretations. Compound-specific stable isotope analysis of amino acids (CSIA-AA) has emerged as a valuable tool for reconstructing key ecological traits, such as trophic position (TP), in individual foraminiferal species. Our study represents the first attempt to apply CSIA-AA to fossil foraminifera by targeting the organic material bound to foraminifera tests, which is sheltered from external influences by the calcium carbonate shell. One of the challenges of applying this technique is distinguishing between primary and removing sediment-derived AA. We tested five different cleaning procedures (gentle rinse, ultrasonication, oxidative, oxidative applied to crushed tests, and oxidative + reductive) using mixed species samples collected from the Santa Barbara Basin (34°14’42.14’’ N, 120°03’33.45’’ W, Northeast Pacific; sediment depth: 0-15 cm). We quantified the AA remaining in each sample following cleaning and the δ15N value of each AA. We conclude that the ultrasonication technique best preserves shell-bound AAs while removing sediment-derived AAs. The AA δ15N values of a monospecific sample of G. bulloides cleaned with ultrasonication were compared with the mixed species cleaning experiments, bulk sediment from Santa Barbara Basin, and monospecific samples of G. bulloides from sediment traps (34°14′26″ N, 119°50′20″ W, ~400 m deep). The foraminifera samples were distinct from the bulk sediment and differed somewhat between mixed species and monospecific samples. The calculated TP of the sediment core sample G. bulloides (2.0) aligns well with the expected trophic behavior of this species as a primary consumer, and is reproducible across shells recovered by sediment trap and sediment core. These results demonstrate that CSIA-AA applied to fossil foraminifera offers a powerful approach to increase our knowledge of past foraminifera ecology and hence refine and enhance the interpretation of paleoenvironmental records. As further proof of concept, our protocol has been applied to three abundant species of extinct planktonic foraminifera (Globigerinatheka mexicana, Subbotina corpulenta, and S. gortanii) from Eocene age material (Site U1408, North Atlantic), with preliminary results to be presented.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413380

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