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PhD Defense

ESS – University Oral Examination - Nicole Travis, May 24 @ 1pm - Y2E2 299

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Stanford University

*** Ph.D. Thesis/ Oral Defense ***

Understanding the contribution of microbial processes to the concentration and isotopic composition of nitrite in the surface ocean 

 

Nicole Travis

Wednesday, May 24, 1:00 pm

Y2E2 Room 299

Department of Earth System Science

Advisor: Dr. Karen L. Casciotti

 

 

Nitrite is a key intermediate in many biological reactions in the marine nitrogen cycle, yet nitrite does not typically accumulate to measurable amounts in the ocean. While oceanographers have observed a consistent nitrite accumulation at the base of the euphotic zone for decades, we still do not fully understand what controls the formation and maintenance of this feature. In this dissertation I investigate the major microbial processes that produce and consume nitrite in the oxygenated surface ocean of the eastern tropical North Pacific (ETNP) in order to understand the relative response of key microbial groups to fluctuating environmental conditions and their net effects on nitrite accumulation in the primary nitrite maxima (PNM). The highest net nitrite production rates were observed near the depth of the PNM, where ammonia oxidation is a dominant process. However, high net nitrite production did not correlate with high concentrations of accumulated nitrite. The integrated signal of microbial activity recorded in the natural abundance isotopes of nitrite over weeks to months was used to calculate relative rates of production and consumption processes, resulting in rate estimates of similar magnitude to directly measured rates. Understanding the balance in microbial processes contributing the PNM refines our estimates of nitrate-fueled primary production and will help identify conditions that may cause increased nitrous oxide production in the surface ocean.

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199508