Award: OCE-0961555

Outcomes of Intellectual Merit Carbon, nitrogen, and phosphorus are essential nutrients for all living organisms and their concentration in seawater sustains marine life. A large fraction of these nutrients in seawater is present as dissolved organic compounds (DOM). In this project, we cultured photosynthetic organisms with very different ratios of carbon, nitrogen and phosphorus and harvested their biomass. We then added this material to water collected in the nutrient poor North Pacific subtropical gyre and the nutrient rich coastal waters. We determined the concentrations of DOM, and the DOM makeup. We also conducted experiments in the laboratory to measure production of the greenhouse gas, methane. The goals of many of these experiments at sea and in the laboratory were to understand how heterotrophic bacteria, organisms that require DOM for growth, decomposed the organic matter generated from these different types of microorganisms. These experiments are akin to asking bacteria if they are what they eat or do they maintain a fixed elemental composition. We were also trying to measure specific by-products of DOM decomposition in the sea. These experiments resulted in a number of scientific findings including but not limited to the following: (1) We now understand how keystone microbes of the genus Trichodesmium and Peligabacter compartmentalize the element phosphorus and how the consumption of specific types of DOM results in the production of methane; (2) We have characterized the makeup of organic compounds produced by different organisms and the temperature dependence of the decomposition rate of specific types of DOM; this helps us model this process (3) We have confirmed that specific microbial populations preferentially release phosphorus before carbon and nitrogen; (4) We have shown that the ratio of carbon, nitrogen and phosphorus in heterotrophic bacteria is independent of the ratio of elements in specific types of DOM. These findings are all presented in peer-reviewed scientific journals. In sum, this research has greatly expanded our knowledge of how marine micro-organisms acquire nutrition for growth and how elements are recycled in the ocean. Outcomes of Broader Impacts As a component of this project, senior personnel trained graduate students, high school students and undergraduate students. Students participated in laboratory and field experiments, with two students participating in research cruises. This project also resulted in the development, testing, use, and sharing of a K-12 education kit: æPhosphorus in our WatersÆ. This kit was utilized at local high schools and at the' Expanding your Horizons' workshop for middle school girls in Santa Cruz, California. Six peer-reviewed manuscripts and two graduate theses were published as a result of this work. One of these manuscripts (Burkhardt et al. 2014) was one of the top 25 'Hottest articles' (#18 of 25) in 2014 for the journal Marine Chemistry. We have also shared results from this work at multiple meetings and as a component of the Saturday Academy summer training workshop for high school students. Products (other than publications) Data from open ocean remineralization experiments were submitted to BCO-DMO (http://www.bco-dmo.org/dataset/557070). Phosphorus in our Waters. A Science kit for K-12 outreach produced in collaboration with the Center for Microbial Oceanography and Education Last Modified: 05/06/2016 Submitted by: Adina Paytan