Title: Can marine microbial communities tell us about diapycnal mixing?
Blooms occur in the oligotrophic open ocean, despite strong stratification in the warm summer months. Two nutrient sources that potentially fuel these blooms include nutrient upwelling and biological N2 fixation. These processes were targeted using a combination of experimental manipulations and high-resolution in situ sampling in the North Pacific Subtropical Gyre. In this talk I’ll describe surprising results that point to the importance of biological interactions in stimulating N2 fixation rates and transcription from N2 fixers. An upwelling event was detected in situ between two eddies during this cruise and the surface microbial community associated with this event was sampled using high-resolution autonomous instrumentation. The microbial metatranscriptomic response to this event was extremely similar to the response of the surface community to deep water mixing in on-deck incubations. Our data suggest that transcriptional patterns from natural microbial communities may serve as signatures of recent deep water mixing events that fuel phytoplankton during the North Pacific bloom. Based on these signatures, we posit that mixing occurs with much higher frequency than previously recognized in the region.