Underwater coded aperture miniature mass spectrometer (UW-CAMMS)

Duke University, Durham NC

Investigators

Abstract

Measurements of the spatiotemporal distribution of dissolved gases in the ocean provides essential information relating to a wide variety of scientific questions of relevance to global climate, plate tectonics, hydrologic circulation patterns, and oil spill plume tracking and monitoring, to name a few. Measurements of dissolved methane in the ocean are of particular importance in that methane is 84 times more potent as a greenhouse gas than carbon dioxide. With increasing ocean temperatures associated with global warming, large gas hydrate reservoirs on the ocean floor could potentially release more methane into the water column. Currently, it is not clear how much methane is being released by gas hydrates (let alone if it is increasing), and how much of it is being oxidized before reaching the ocean surface where it can be released into the atmosphere. Oxidation of the methane below the ocean surface may lead to ocean acidification, thereby impacting marine organisms, while release to the atmosphere could alter climate. Hence, assessment of the relative concentrations of methane below the ocean surface and in the ocean surface mixed-layer has important ramifications for our understanding of how gas hydrates may impact marine ecosystems and the feedbacks to our global climate. in situ measurements are highly desirable as laboratory-based measurements reduce the spatiotemporal resolution and increase time and cost of measurements. Over the past 20 years, underwater membrane inlet mass spectrometry has emerged as the primary method for in situ analysis of dissolved gases in the ocean due to their ability to measure the concentrations of a wide variety of gases with high sensitivity (1 ppb) and rapid response times. However most currently available underwater mass spectrometers are not ideal for measurements of dissolved methane due to limited mass range, resolution, and/or interference from water vapor. This project will be used as a platform for enhancing education across multiple academic levels and disciplines by providing research opportunities for high-school students, undergraduates, graduate students, and post-doctoral researchers and will be leveraged towards broadening the participation of underrepresented groups, particularly women and underrepresented minorities. This research will develop an underwater coded aperture miniature mass spectrometer (UW-CAMMS) using a cycloidal mass analyzer, spatial aperture coding, and a focal plane array detector that combined will improve sensitivity, resolution, and power requirements compared to the current state of the art underwater mass spectrometers used for in situ measurements of dissolved gases in the ocean. The higher resolution will eliminate the issue of interference from water vapor in measurements of methane. The spatial aperture coding in UW-CAMMS will increase sensitivity by increasing ion throughput without sacrificing resolution and the ion array detector in UW-CAMMS will enable simultaneous detection over a wide mass range with high sensitivity and dynamic range. Once developed, UW-CAMMS will be deployed on the R/V Shearwater for field testing and to study methane profiles in the waters above Blake Ridge off the coast of North and South Carolina. 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.