Award: OCE-2122427

This project made use of a unique scientific resource: deep-ocean gas samples collected in the 1980s and 1990s by extracting dissolved gases from large volumes of seawater at many locations throughout the deep Atlantic Ocean. Those gases were sealed and stored for decades, creating an archive of deep-water composition that has remained largely unexplored. We applied modern analytical approaches across four separate instruments to assess the preservation of these samples, to uncover new patterns in the distribution of dissolved gases in the deep ocean, and to build a lasting archive and catalog that make these samples available to researchers worldwide.

Our analyses showed that the gases have remained exceptionally stable over time. Measurements of noble-gas ratios allowed us to correct for small artifacts introduced during the original extraction process, improving the accuracy of comparisons between different regions and depths. With these corrections in hand, the samples revealed new insights into deep-ocean processes. In the deep North Atlantic, we identified a consistent increase in excess dissolved nitrogen with water-mass age. This pattern suggests that denitrification occurring within deep-sea sediments may contribute more significantly to the oceanic nitrogen cycle than previously recognized.

We also observed strong spatial variations in the triple-oxygen-isotope composition of dissolved oxygen. Rather than being controlled only by gas exchange at the sea surface when deep water is formed, the oxygen-isotope signal appears to carry a biological imprint that is retained as the water flows through the ocean interior. Deep waters of southern origin show particularly elevated values, indicating that the history of oxygen consumption and production in surface waters can remain detectable long after the water has left its formation region. These results open new avenues for investigating the connections between ocean biology and deep-water transport pathways.

A major outcome of this award was the preservation and enhancement of the gas archive itself. We established a well-documented physical collection and an online catalog that provide clear routes for other scientists to access samples for future tracer studies. The project also delivered important educational benefits: it supported a Ph.D. student, two undergraduate summer researchers, and another undergraduate who is leading publication of the oxygen-isotope findings. The work further advanced laboratory capabilities through the development of improved methods and experimentation with a miniature gas-extraction device designed to quantify fractionation effects during seawater degassing.

In sum, this project demonstrated that decades-old deep-ocean gas samples remain a powerful resource for learning about ocean circulation and biogeochemical transformations. By combining careful archiving, methodological innovation, and new scientific results, it expanded the tools available to the marine chemistry community and created lasting opportunities for continued discovery.

 

 

Last Modified: 12/09/2025
Modified by: Alan Myland Seltzer