Award: OCE-1635562

For this research project, we focused on a fundamental question. Do cyanobacteria drive marine hydrocarbon biogeochemistry? The outcome of our research efforts convincingly demonstrate that the answer is yes – cyanobacteria drive marine hydrocarbon biogeochemistry. To enable this research, new chemical oceanographic techniques were needed. As such, we developed new approaches to quantify cyanobacterial hydrocarbons in seawater, and we developed new isotope-based approaches to quantify production rate of cyanobacterial hydrocarbons in seawater. In applying these approaches to the subtropical north Atlantic gyre we reached several conclusions. i) We demonstrate that primarily one hydrocarbon compound, pentadecane, is produced in the sunlit surface of the subtropical north Atlantic ocean; ii) We demonstrate that Prochlorococcus and Synechococcus both produce pentadecane; and iii) We demonstrate that pentadecane distribution and productivity exhibit depth dependence related to the physiology of Prochlorococcus. Extrapolating these findings to the global scale we reached additional important findings. Notably, we find that the quantity of pentadecane produced by cyanobacterial in the oligotrophic surface ocean is roughly 500 times greater than the totality of petroleum hydrocarbons released to the ocean by all sources. This finding has major implications for the ability of the ocean to respond to petroleum inputs, notably that alkane consumption is expected to be ubiquitous based on widespread priming, but leaving open the question as to whether dissimilar hydrocarbons will exhibit distinctive behavior. The broader impacts of this research focused on the education and training of both graduate and undergraduate students, and included participation of six students on a major oceanographic research expedition, and training of additional students in the laboratory setting. Broader impact activities involved the integration of teaching and research. Last Modified: 12/22/2020 Submitted by: David L Valentine