Collaborative Research: Development of a New Instrument for Underway High-Resolution Estimates of Aquatic Gross Primary Production

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Photosynthesis is arguably the most critical biological process of our climate system. It is also central to the trophic and metabolic states of ecosystems. Refining estimates of photosynthesis is therefore critical to our understanding of biogeochemistry and the global climate. Spatial variability of photosynthesis is difficult to resolve due to limitations in technology; the development of high-resolution instrumentation is needed to close this gap. To characterize the geographical distribution of marine photosynthesis, this research will develop an instrument for underway shipboard measurements of aquatic photosynthesis by spectral monitoring of dissolved oxygen (O2) isotopes. Named GOPTICAS (Gross Oxygen Production by Triple Isotope Cavity ringdown laser Absorption Spectroscopy), this instrument will allow for high-resolution observations of photosynthetic O2 evolution, or gross primary production (GPP) by monitoring the dissolved O2 triple isotope signature by wavelength-scanned cavity ring-down absorption spectroscopy (CRDS). The new instrument will extract dissolved O2 into a dried gas stream, then convert it to water (H2O) in a fuel cell downstream of which the isotopic signature of the produced water (H2O) will be monitored with a CRDS. GOPTICAS will 1) provide high-resolution, near real-time and precise mapping of GPP rates to guide sampling strategies, 2) allow for simple field deployment, and finally 3) can be duplicated by other research groups interested in GPP in marine and freshwater ecosystems. Measurements directly in the field will also limit artifacts associated with sample handling and long-term preservation. The instrument will be tested on short cruises aboard the R/V Shearwater in Pamlico Sound and in the Gulf Stream, and on Northeast Shelf LTER cruises. GOPTICAS will improve the characterization of the biogeography of marine photosynthesis, a microbial process with profound biogeochemical implications. Once developed and validated, GOPTICAS will help constrain the global carbon budget and ultimately improve our mechanistic understanding of the feedbacks and coupling between photosynthesis and climate and, in the process, inform and challenge models of ocean biogeochemistry. Finally, this study will be used as a platform to 1) broaden participation in STEM among a diverse population of High School and Undergraduate students through creation of research-based, experiential learning opportunities in engineering and environmental science, 2) teach our lab members how to communicate climate science to the public, and 3) collectively engage students and the public in a discourse about climate change, one of the most pressing issues facing our society in the 21st century.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.