Autonomous Measurement of Physically and Biologically Driven Changes in Dissolved Oxygen in the Northern Gulf of Mexico

The emergence of miniaturized biogeochemical sensors and their integration into piloted and autonomous platforms such as gliders and profiling floats has opened new avenues for measuring primary production. The key variable for determining production through autonomous measurements is oxygen, which can provide the necessary information via diurnal or long-term changes in concentration. To date, such production estimates have either been means over extended time periods, or, on shorter timescales, used mixed layer measurements only. Here we report on attempts to estimate daily production in the entire euphotic zone using biogeochemical profiling floats. The floats were deployed in the northern Gulf of Mexico and programmed to rapidly sample over several multi-day periods in order to measure short-term variations in upper ocean oxygen concentration. We first assess the viability of the observing platform and optode sensor for estimating primary production from a technical angle, and present a novel method for determining and correcting for the response time of the oxygen optode. Then, the manifestation of different processes affecting dissolved oxygen is discussed from an oceanographic perspective. Analysis of the measurements is combined with a simple, one-dimensional numerical model to examine the relationship between sampling rate, sensor accuracy, and resulting estimates of primary production.