Microbial diversity and biogeochemistry through a transition zone in the North Pacific


The North Pacific Subtropical Gyre is the largest ecosystem on the planet, and it is also one of the “deserts of the ocean,” harboring low surface nutrients and low rates of primary productivity driven primarily by cyanobacteria. North of this ecosystem is the North Pacific Subarctic Gyre, where water is colder and higher in surface nutrients, and where larger-celled, iron-limited phytoplankton drive higher rates of productivity. The “Gradients” project is bringing together a team of biologists, chemists, and modelers to track and predict gradients in microbial diversity and biogeochemistry in the transition zone between these two ecosystems. The transition zone harbors a distinct community of microorganisms (e.g. Synechococcus dominance) and may have a disproportionately large impact on the biogeochemistry of the North Pacific. The figure below shows the distribution of small phytoplankton in the Subtropical Gyre, transition zone, and Subarctic Gyre on a 2017 cruise along 158°W.

The Zehr lab is particularly interested in how communities of nitrogen-fixing bacteria vary along this transect. The warm, low-nutrient waters of the Subtropical Gyre are a classical habitat for cyanobacterial nitrogen-fixers, but these organisms are often not detected in the cold, higher-nitrate waters of the Subarctic Gyre. We are using high throughput sequencing and FISH-based methods to investigate the diversity, abundance, and activity of marine nitrogen-fixers in stations from the Subropical Gyre, transition zone, and Subarctic Gyre.


This research is funded by the Simons Foundation.