Award: OCE-0961221

Isotopes are variants of an element that have different masses. The so-called stable isotopes of an element (those not subject to radioactive decay) can be separated by chemical and biological processes. Oxygen has three stable isotopes. Ratios of oxygen gas molecules dissolved in seawater that have different isotopic abundances can be used to monitor the total mass of biological activity in the oceans. This is because photosynthesis is a source of oxygen and respiration is an oxygen sink, and both processes affect the isotopic composition of oxygen. In this project we used this "proxy" of oxygen isotopes for biological productivity to investigate the carbon cycle in the Eastern Tropical South Pacific. Combined with other chemical tracers, we find higher total biological productivity in La Nina conditions in 2011 compared with El Nino in 2010. This oxygen isotope approach was also used by us to document drawdown of carbon in the oceans where outflows from the Amazon River cause bacterial blooms. The blooms driven by riverine outflows accelerate the carbon dioxide "pump" in the oceans by which dissolved carbon (from CO2) is sequestered in sinking organic particles, thus transporting carbon from the near-surface to deeper in the ocean basins. The methods used in this study are analytically challenging. Development of highly precise oxygen isotope ratio measurement capabilities at UCLA resulted in promulgation of this technology to the next generation of geochemists. Last Modified: 12/06/2012 Submitted by: Edward D Young