Award: OCE-1756816

Final outcomes report

This project focused on the fate of the carbon associated with a major group of phytoplankton, the diatoms. The major objective is to understand how diatom community composition and the prevailing nutrient conditions create taxonomic differences in metabolic state that combine to direct diatom taxa to different carbon export pathways.

It is hypothesized that the type and degree of diatom physiological stress are vital aspects of ecosystem state that drive carbon export. To test this hypothesis, phytoplankton physiology, genomics and trace element chemistry were used to assess the rates of nutrient use and the genetic composition and response of diatom communities, with measurements of silicon and iron stress to evaluate stress as a predictor of the path of diatom carbon export. The research leveraged the NASA Export Processes in the Ocean from RemoTe Sensing (EXPORTS) field program directed at quantifying the export and fate of primary production in the upper ocean and allowed us to follow diatom fate through multiple export pathways including sinking of single cells, sinking aggregates and grazing.

 The research was conducted in two contrasting oceanographic regions: the subarctic N. Pacific ecosystem that is characterized as high nutrient low chlorophyll (HNLC) due to low iron (Fe) levels that are primary controllers constraining phytoplankton utilization of other nutrients. We also conducted a field campaign in the North Atlantic during a spring bloom where silica, a major nutrient required for diatom growth, was in ample supply along with other nutrients at the beginning of the sampling and depleted at the end. We identified diatoms that persist in low iron in the N. Pacific that bloom rapidly when iron is added. Patterns of gene expression between sampling times that grouped by diatom genera rather than sampling date indicating the stability of the community and that diatoms evolved distinct responses to nutrients to allow them to thrive in the iron-limited niche. Genera-specific responses to iron addition were observed in pathways for photosynthesis, glycan metabolism, amino acid metabolism, lipid metabolism, carbohydrate metabolism and oxidative phosphorylation.   The dynamic silica depletion in the North Atlantic revealed new pathways for diatom silica metabolism that have implications for phytoplankton growth globally.

Broader impacts include training of several early career scientists and undergraduates, presentations to audience including the general public and development of tools, pipelines and methods for data intercomparison. All data from the project have been made publicly available and will contribute to synthesis efforts across the EXPORTS program studies to gain a more predictive understanding of how the biological pump operates and to enable assessments of how the ocean sequesters carbon.

 

Last Modified: 01/28/2025
Modified by: Bethany D Jenkins