Why?
Why does it work this way? A mechanistic understanding of microbial nitrogen cycling in OMZs
Building on the in situ observations from “How,” this task aims to develop a mechanistic understanding of the biological and chemical controls on microbial nitrogen cycling in oxygen minimum zones (OMZs). These processes are critical for predicting present and future nitrogen loss from the ocean.
Understanding growth and mortality of nitrogen-cycling microbes
We still know very little about how quickly nitrogen-cycling microbes grow, how efficiently they use nutrients, or what controls their mortality in OMZs. Because many microbial groups compete for the same compounds, these interactions strongly influence whether nitrogen is recycled within the ecosystem or permanently lost from the ocean.
Therefore, we will examine how nutrient availability, microbial growth, competition, and mortality regulate nitrogen cycling in OMZs. Combining single-cell measurements with community-level process rates will provide critical data for improving global ocean models.
Understanding incomplete denitrification pathways
Denitrification is a major pathway of nitrogen loss and N₂O production in OMZs. By linking rates of individual nitrogen-oxide reduction steps with single-cell enzyme activity and growth rates, we will provide the first direct measurements of denitrifier growth and activity in the ocean.
Investigating hidden oxygen sources in OMZs
Although nitrifying microbes require oxygen, they are commonly found in OMZ waters. In addition to quantifying physical oxygen supply to OMZs using autonomous glider observations (“How”), we investigate hidden biological oxygen production with stable-isotope experiments in field incubations and laboratory cultures to determine its importance in sustaining aerobic nitrogen cycling in OMZs.
