Oxygen and Carbon-based Production and Respiration Rates Across the Pacific Ocean from Profiling Floats

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Ocean chemistry and biology play an important role in the global carbon cycle. This project will characterize key components of biological carbon cycling in the Pacific Ocean. The team will use profiling floats (autonomous vehicles equipped with several sensors) to measure oxygen and particulate carbon concentrations and estimate the amount of carbon and oxygen produced, consumed, and lost by algae, bacteria, and other organisms in the top 200 meters of the ocean on a day-to-day basis across all seasons. They will also make direct measurements of these daily quantities and other properties from a research ship. The ship-based measurements will be used both to calibrate the float measurements and to determine how the ratio of oxygen produced to carbon dioxide absorbed during photosynthesis, as well as the ratio of oxygen utilized per organic carbon molecule consumed during respiration, vary over space. These quantities are poorly understood and are rarely measured but are critical to determine marine ecosystem health. In addition to allowing measurements over a full seasonal cycle, the float data will support validation of satellite-based methods for estimating carbon production over broad areas of the ocean. Collectively these efforts address the critical need for better understanding how ocean productivity changes over time and space and how much carbon is sequestered to the deep ocean due to biological processes. The project will include active participation of graduate and undergraduate students at sea. The researchers will also participate as mentors in the Indigenous Partnership for Ocean Monitoring led by the Consortium for Increasing Research and Collaborative Learning Experiences, CIRCLE, program at the University of Hawai’i. This program engages local high school students to conduct research to learn about the connection between their health and the health of the ocean. Students will be trained to analyze float and satellite data. In order to determine the metabolic state of global oceans over time and space, we must be able to accurately characterize both primary production (PP) and community respiration (CR) rates. Spatial and temporal variations in PP are poorly known because the effort required for the traditional carbon and oxygen-based bottle incubation methods limits their application. Satellite-based PP estimates on which we rely for regional and global patterns are poorly validated and can be inaccurate. Building upon preliminary work demonstrating that diel cycles of dissolved oxygen and optically-derived particulate carbon obtained via autonomous profiling floats can yield reliable estimates of gross production (GP) and community respiration (CR) rates in the North Pacific Ocean, the team plans to resolve the seasonal cycle of GP and CR across the Pacific basin using long-term float deployments programmed to obtain diel-resolving measurements of oxygen and particulate carbon throughout the euphotic zone. Previous ship-based work in the subtropical and subpolar North Pacific regions found ecosystems marked by consistent production to respiration ratios, which was unexpected given the approximately 10-fold increases in biomass, particulate carbon, and chlorophyll, and 50-fold increase in nitrate across the region. It is unclear how these ratios may vary over time, whether patterns extend to the Equatorial and South Pacific oceans, and what role dissolved organic matter production and respiration, particle export, and phytoplankton composition may have in driving and/or biasing measured rates. Together, float-based rates and ship-based experiments will shed light into those unknowns, allowing an unprecedented view into basin-scale ecosystem functioning. The team expects to obtain approximately 70 oxygen-and carbon-based daily rates per float per year over the seasonal cycle, potentially revolutionizing our understanding of how production and respiration rates vary over time and space. This effort will showcase a powerful means to evaluate satellite-based PP estimates across vast areas of the ocean, which has been critically needed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.