MRI: Development of an Ultra-High-Precision Gas Mass Spectrometer

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This Major Research Instrumentation award supports development of a next-generation gas mass spectrometry system with sufficient precision to measure the rate of ocean warming due to fossil fuel burning. The method works by measuring the atmosphere's krypton and xenon abundances over time, which are rising due to the fact that warm water holds less dissolved gas than cold water. These measurements complement the direct ocean temperature observations from floats and ships with a completely independent method, which takes advantage of the well-mixed nature of the atmosphere to track volume-average ocean heat at a single location. Given that 93% of the excess heat from greenhouse gases ends up in the ocean, this approach is a cost-effective way to add confidence to society's knowledge of this crucial planetary vital sign. The gas mass spectrometry system also enables measurement of past atmospheric oxygen concentrations from trapped air in ice cores, which will improve scientific understanding of release of greenhouse gases from soils as they warm. Broader impacts of the work include education of one PhD student, and the research career development of two under-represented minorities who will use the instrument. The inventory of excess ocean heat reflects in a rather direct way the cumulative energy imbalance at the top of the atmosphere due to human radiative forcing. In principle, a better knowledge of ocean heat content over the past half century would narrow the uncertainty on the estimate of sensitivity, which has been at 3+-1.5 degrees C for the last 50 years. Archived air samples taken by the Scripps CO2 program over the past 50 years will be measured for krypton and xenon concentration, using the proposed equipment, to see if it is possible to improve the historical record of ocean heat, and thereby reduce the uncertainty on the sensitivity. The technological strategy is based on purchase of a factory-modified MAT 253 Ultra mass spectrometer, combined with a custom pressure-stabilized inlet system already in use at the Scripps Institution of Oceanography. A parallel conventional inlet system will enable frictionless shared use of the instrument for other purposes, such as gas measurements that require high mass resolution to separate interfering masses from the species of interest, or studies of rare isotopologues and mass-independent fractionation. This proposal will establish a shared-use Facility for Advanced Isotope Geochemistry at Scripps, which will underpin transformative new discoveries and attract young researchers.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.