Award: OCE-1948842

The marine carbon and oxygen cycles are intimately linked through the production and consumption of oxygen during photosynthesis and respiration. The amount of oxygen consumed per mole of respired organic carbon, the respiration quotient, is key for accurately predicting ocean oxygen concentrations and how ocean oxygen levels will respond to climate change. Despite this importance, the respiration quotient has rarely been measured directly. This project supported participating in several long Bio-GO-SHIP section cruises to the Atlantic, Pacific and Arctic Ocean. Here, we measured the respiration quotient along with environmental factors and phytoplankton biodiversity. We observed that the respiration quotient was regulated by hierarchy of environmental factors. Temperature emerged as the primary driver with a higher respiration quotient in the tropics and subtropics. This finding could mean more intense oxygen depletion as the ocean is warming. However, we also identified that the respiration quotient was higher in N compared to P limited regions. Another aspect of this project was to use large-volume pumps to quantify the respiration quotient in particles deeper in the water column. While we hypothesized a decline in the respiration quotient due to partial oxidation of organic matter, we did not find support for this idea. Instead, we observed complex non-linear shifts with depth. Finally, we worked with a local state park and developed a new educational module about the importance of oxygen for ocean life. This module is now being used by students visiting the park. Overall, our project has clearly demonstrated that the respiration quotient is not constant. The temperature effect suggests a possible future increase, but the role of nutrient limitation and vertical transport add a lot of uncertainty to such a prediction. Last Modified: 07/14/2023 Submitted by: Adam C Martiny