I am a postdoctoral research associate with the Southern Ocean Carbon and Climate Observations and Modeling project. My research centers on understanding ocean biogeochemical cycles through a combination of sensors on autonomous vehicles, in situ measurements, and using models of varying complexity to understand our observations. One of the main aspects of the carbon cycle that we seek to understand is the biological export of organic matter. This export is also known as annual net community production (ANCP), because it represents the total difference between organic matter fixed by photosynthesis and that consumed by respiration over the course of a year.
We can estimate ANCP by making use of the stoichiometric relationship between organic carbon fixation, oxygen production, and nutrient utilization. Oxygen and nitrate (one of the macro nutrients needed by phytoplankton) are relatively easy to measure and can be used as proxies for the integrated changes in the net community production of a system.
Recent advances in sensor technology have allowed oxygen and nitrate measurements from Argo profiling floats. These floats make measurements of temperature, salinity, oxygen, nitrate, and in some cases pH, every 10 days from 2000 meters to the surface. Using these measurements, we can start to constrain the biological carbon cycle and greatly improve our understanding of fundamental biogeochemical processes.
In order to use and interpret these data, several developments have been necessary. First, oxygen sensors are known to drift prior to deployment and we have collected recent evidence that they continue to exhibit smaller rates of drift post-deployment. To deal with drift, during my PhD with Steven Emerson at the University of Washington, we developed and deployed Special-Oxygen-Sensor Argo floats designed to use atmospheric oxygen to calibrate their sensors after every profile.
To interpret these data, we need to account for the physical processes that impact oxygen and nitrate. We developed a 1-dimensional box model of upper ocean processes that allows us to isolate the biological signal by modeling the oxygen and nitrate concentrations we would expect in the absence of biology and comparing those estimates to our actual measurements from profiling floats. This involves careful accounting of air-sea processes such as gas exchange, which we do by comparing different gas parameterizations to mooring gas data and in situ measurements of noble gases.