Project: Collaborative Research: Inventories of Primary Productivity by In-situ Mass Spectrometry in the Upper Ocean

NSF Award Abstract:

Production of organic matter from carbon dioxide (specifically by photosynthetic organisms) and respiration of organic matter back to carbon dioxide (by a wide variety of organisms, including photosynthesizers) are very nearly in balance over much of the ocean -- but not quite. In some regions remote from land, more carbon is produced through photosynthesis than is respired back to carbon dioxide; in others, just the opposite is true. Figuring out which is exceedingly important because in regions where photosynthesis exceeds respiration, there is a net production of food for marine life as well as a net removal of carbon dioxide (a powerful greenhouse gas) from the atmosphere. Conversely, oceanic regions where respiration exceeds photosynthesis are zones of net food consumption and release of carbon dioxide to the atmosphere. In practice, the problem is that the differences, one way or the other, are so small that it is difficult to distinguish between the measurements themselves and noise (that is, scatter) in the data. Resolution of this problem requires new technology that can make the necessary measurements with very high precision in the ocean itself rather than in a bottle of sampled seawater. In this project, the investigators will attempt to do just that using a sophisticated instrument normally found only in an analytical laboratory -- a mass spectrometer, a device capable of making ultra-high-precision measurements of changes in the amount of dissolved oxygen, carbon dioxide, and other substances associated with photosynthesis and respiration in the marine water column. The investigators will support graduate students to participate as integral members of the research team. There will also be public educational outreach to secondary school students offering them the opportunity to engage with the project to gain first-hand experience seeing how the basic sciences can be used to solve oceanographic problems.

In this project, a team of investigators will evaluate one facet of these methodological concerns using in-situ mass spectrometry to better constrain net community production (NCP). The UMIMS is a fast-response Underwater Membrane Inlet Mass Spectrometer that can be deployed in autonomous and remotely-operated vehicles. In this application, UMIMS will be deployed aboard a SeaSoar tow vehicle to make high resolution vertical sections of the excess dissolved oxygen (O2) over argon (Ar) budget, a promising measure of NCP in the surface ocean. Profiles with the UMIMS can provide the capacity to resolve processes throughout the mixed-layer and euphotic zone that affect the NCP budget. In the near term, the team will utilize the capabilities of the UMIMS to make accurate and simultaneous mixed layer profiles of O2 and Ar and compare measurements of NCP from the UMIMS with measurements from the conventional shipboard O2/Ar budget from underway seawater. These comparisons will be used to determine the limitations of both methods and the degree to which they can resolve the ambient physical processes leading to non-stationary exchange. In the long term, the researchers expect to make the technological and methodological advances necessary to deploy the UMIMS on Lagrangian floats and sea gliders. As such, this project is expected to make a significant step toward measuring near-continuous time and space series observations of the oceanic metabolic balance and the biological pump, similar to the way Argo floats measure temperature and salinity today.