Award: OCE-1851210

Subsurface regions of the ocean with very low oxygen concentrations are important in setting the overall ocean nutrient balance.In particular, in regions of very low oxygen, unique microorganisms convert dissolved nitrogen, the major fertilizer of ocean productivity, into nitrogen gas, thereby decreasing the amount of fertilizer.These regions appear to be expanding and thus need to be monitored as the oceans change. This could be done using existing arrays of robotic profiling floats, but the sensors on these floats are not optimally chosen for this problem.This grant funded the further development of new calibration techniques for standard commercial oxygen sensors, the development of a new sensor for measuring nitrogen gas and the construction and deployment of oceanographic floats to carry these sensors. A total of 16 floats were deployed in the Pacific Ocean off Mexico and Central America on two cruises in 2021 and 2022 at the height of the pandemic.Other measurements on the cruises, mostly at low cost by international collaborators, allowed us to compare the observations from the new sensors with more traditional measurements.Although not all the floats worked well, there was sufficient data to show that the new oxygen methods increase the sensitivity of the oxygen measurements by a factor of 10 and that the new nitrogen gas sensor can measure the excess nitrogen gas produced in the measurement region.The float and ship data together resulted in a much better mapping of the geography and structure of the ocean minimum zone in this region and the first detailed mapping of the region of lowest oxygen. The Intellectual Merit of this work is an increased understanding of how to measure these gasses and a much more detailed view of the geography of the region of lowest oxygen in the study area. The Broader Impact of this work is a new scheme for calibrating oxygen sensors which can be applied to thousands of existing oxygen profiles, and a demonstration of how to monitor regions of low oxygen in the ocean using robotic oceanographic profiling floats. Last Modified: 07/25/2024 Submitted by: EricD'asaro