I’m Seaver Wang, a graduate student in Dr. Nicolas Cassar’s research group at Duke University’s Division of Earth and Ocean Sciences. In my research, I am interested in measuring rates of marine carbon and nutrient cycling and relating these processes to the microbial diversity of the surface ocean. In addition to this project examining El Niño and the California current, I am also studying nitrogen and phytoplankton activity and taxonomy in the Sargasso Sea, a region of the western North Atlantic. My project aboard the Sikuliaq involves operating an instrument designed to measure “net community production” in the surface ocean using a method called equilibrator inlet mass spectrometry, or EIMS.
Net community production, or NCP, is the balance between biological rates of photosynthesis and respiration taking place in the upper, well-mixed portion of the sea. For instance, if photosynthesis exceeds total respiration, the resulting positive NCP represents an overall uptake of carbon by marine biota. Using a mass spectrometer, I analyze dissolved gases from seawater collected continuously from an intake near the ship’s keel. The instrument measures the ratio of oxygen—which is consumed and produced by biological activity—to argon. Argon is a relatively inert compound that has similar solubility characteristics to oxygen gas but goes completely unused by marine biota, unlike oxygen. Therefore, differences in the ratio of oxygen to argon can largely be isolated to biological activity. Using the O2/Ar ratio measured via EIMS, I am able to calculate phytoplankton productivity, which we hope to compare to measurements of photosynthetic pigments, zooplankton grazing, particle sinking, and microbial community composition that are being conducted by other teams aboard the Sikuliaq.