RAPID: Linking gene expression, silicification, and diatom-bound nitrogen isotopes in field isolated diatom species from the Southern Ocean

Diatoms are microscopic algae that live in oceans and other aquatic environments. Different diatom species thrive in different conditions, and so diatom fossils can be used as historical records of ocean environments, including the availability of nutrients such as nitrogen and silicon that are important components of ocean ecosystems. This RAPID proposal aims to understand how environmental conditions and the species of diatom may impact these records. The investigators will use recently collected samples from the Southern Ocean to determine how different species react to varying amounts of nitrogen and silicon. These culture-derived data will then be used to ground-truth field-collected data. This is expected to improve our use of diatom fossil information to understand past ocean conditions. Diatom fossils provide information on past surface ocean nutrient conditions through the analysis of cell-bound nitrogen and silicon isotopic composition of frustules. Recent data suggested that simple fractionation models do not always explain spatial trends or seasonal variation. To improve understanding of isotopic fractionation variability, this project aims to evaluate gene expression, diatom silicification, and diatom-bound nitrogen isotope values under varying nutrient conditions using recently collected, difficult to maintain Antarctic marine diatom isolates. The isolates were collected during the 2024-2025 spring diatom bloom in the Southern Ocean. In addition to accomplishing combined measurements of isotopic relationships and transcriptional response to nutrient conditions for understudied environmentally relevant diatom species, this work will aid in ground truthing in situ cruise data and improve reconstruction of past surface ocean conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.