Award: OCE-1736756

Nitrogen is important for all forms of life. All cells, ranging from the smallest viruses to the largest trees use it to build proteins and nucleic acids. On land, plants take up nitrogen from the soil; in the ocean, plants often rely on nitrogen, in the form of nitrate, found in deep water being delivered to the surface. In this project, we studied the routes of nitrate supply from deep water into the surface waters by measuring the chemical signatures of the nitrate coming from different regions. We can also use those signatures to better understand how much nitrogen can be found in the deep sea and what processes distribute nitrate throughout the deep ocean. We sailed on a 68-day research cruise between Seattle and Tahiti, collecting samples from almost 40 stops along the way. At most stops, we sampled water from the very surface of the ocean, down to its deepest depths. These samples were returned to the laboratory and analyzed. Afterwards, we compared these chemical analyses with other properties of the water samples, such as their temperature, salinity, and dissolved oxygen content to determine where the nitrate in the water had come from and how it got to the point from which we collected it. It is well known that in some regions of the ocean nitrate is plentiful in surface waters and those waters are rich with marine life. In other regions, nitrate is scarce. Our research sampled waters from both nutrient-rich and nutrient poor regions of the ocean. To understand why some areas are so depleted in nitrate, we studied where the nitrate comes from and where it goes, through the analysis of its chemical fingerprint. The nitrate that we study is used by marine plants and algae to grow, which enables them to fix more carbon dioxide. If those algae sink out of the surface ocean, their carbon can be stored in the deep ocean and reduce the amount of carbon dioxide present in the atmosphere. So, by better understanding the delivery of nitrate to surface waters, we can better predict the capacity of marine life to take up and store carbon dioxide in the ocean. Nitrate can also be converted to the greenhouse gas nitrous oxide through several ocean processes. We?re currently exploring the linkages between the distribution of nitrate and the production of nitrous oxide in the ocean. This project involved researchers at Princeton, Stanford, and Brown University. Three female graduate students at Stanford were involved with the research, and they received training in seagoing and laboratory research. They also were involved with collaborations that will benefit their future careers in science and technology. We have reported on our findings to the scientific community and will be releasing our data through public databases that can be accessed by anyone interested in learning more about our work. We also developed a website and used social media to present some of the general scientific objectives of the work and give a sense of how the work at sea was conducted. This can be found by searching for the research program and cruise name, GEOTRACES GP15. Last Modified: 10/28/2023 Submitted by: Karen L Casciotti