CAREER: Organic Matter Cycling in the Upper Ocean: Insights from time-series measurements of d15N and D14C in the California Current System

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The marine dissolved organic matter (DOM) reservoir is often conceptualized as a "capacitor" for carbon because of its potential for storage and exchange with the other active reservoirs. Yet, despite its size and potential importance, the dynamics of DOM have not been fully assessed, and therefore the ultimate role of this reservoir for the global and marine carbon and nitrogen cycle remains to be established. To resolve the dynamics of the complex DOM reservoir, a young investigator from the University of California San Diego will develop a spatially resolved time-series of fraction-specific d15N and D14C measurements of DOM. This time series will be placed within the California Current System which experiences physical/climate variability on a variety of timescales (e.g. seasonal, interannual, decadal). The climate-associated disturbances (deepening/shoaling thermocline or nutricline, changes in wind field) are expected to lead to measurable excursions in the isotopic composition of surface inorganic dissolved CO2 and NO3-pools. These excursions are ultimately recorded by organic matter fractions that are recently produced in surface waters; and when placed within the context of a time series, fraction-specific isotopic variability will, for the first time, directly identify DOM cycling on annual to multidecadal timescales. In addition, the time series will also help identify relative proportions of refractory and young DOM components in surface waters and delineate some of the physical and biological processes that control the size and age of the DOM reservoir. As part of this CAREER award, a new, inquiry based, undergraduate course will be created to place the theoretical coupling between large scale phenomena such as climate-ocean-atmosphere and smaller scale phenomena such as ocean physics-chemistry-biology within a tangible, region-specific, real-world framework. A fundamental goal of this course will be for students to learn experientially how science "works"; students will design class projects that use archived time-series data to explore the above connections and collect oceanographic data on a 4-7 day educational cruise to the California Current System. Among the broader impacts, this study will be one of the most comprehensive, long-term investigations of the interrelation between climate and biogeochemistry. The infrastructure of the larger, ongoing scientific programs in the region will provide context, and enhance the dissemination of scientific data collected as part of this proposal to a broad audience through both web-based tools and written and verbal communication. Through the four specific goals of the Education and Outreach plan, the PI will teach and mentor ~100 undergraduates, mentor ~8 high school students, empower both student groups to be more critical, better environmental decision-makers, provide ~8 educators with valuable scientific experience to take back to their own classrooms and so reach even a larger number of students, and also provide ~100,000 citizens with a valuable window into the marine ecosystem in their own backyards. In addition, the high school students that will be targeted represent some of the most under-served youths in San Diego County.