The current renaissance in mass spectrometry may revolutionize our understanding of modern surface environments and earth’s chemical evolution. Ongoing innovations in analytical instrumentation are increasing both the speed and precision of measurements while decreasing sample size requirements. Three of the most exciting developing technologies are electrospray quadrupole-orbitrap mass spectrometers, the inclusion of a collision-cell on multi-collector plasma machines such as the Sapphire and the Neoma, and high-resolution gas-source instruments such as the Ultra and the Panorama. While each next-generation mass spectrometer will excel in distinct analyses, overall the field of isotope geochemistry seems poised to begin routine measurements of multiple isotope systems on the same samples, including site-specific information, and with less material required than ever before. I am excited to be part of this venture. In particular, I think it would be worthwhile to develop nascent orbitrap methods to robustly measure the major, minor, and clumped isotope composition of river and ocean sulfate, phosphate, and nitrate, as well as to push forward on improving orbitrap and MC-ICP-MS measurements of alkali, alkaline earth, and trace metal isotope ratios. For example, I am interested in using coupled calcium, magnesium, potassium, lithium, and strontium isotopic ratios to study clay formation and reverse weathering, in measuring the clumped isotope composition of intact carbonate ion from carbonate rocks as an improved paleo-thermometer, and in capitalizing on high-throughput iron isotope methods to study pyrite formation and the global evolution of earth’s surface redox environment.

Isotope thermometry has been a tremendously insightful tool for understanding the past. However, thermodynamic variables other than temperature, such as pressure, also influence isotopic distributions. As a result, I am interested in whether isotopic fractionation is ever dominated by these alternative thermodynamic forcings, and whether we can thus study changes in those forcings through space and time. For example, the identification of an isotopic system where fractionation is dominated by changes in pressure, rather than temperature, may allow for the development of a proxy for atmospheric density or paleo-water depth. More imaginatively, identifying a signal of pressure-induced fractionations may indicate the location of paleo-fault lines.

Quantitative interpretations of isotope records are typically built around the mass balance equation d/dt(M*δ) = Σi(Ji*δi), which states that changes in isotopic ratios depend on reservoir size. However, when considering marine isotope curves, there are very few experimental constraints on the concentration of elements in seawater through time. Even our best reconstructions, such those based on halite fluid inclusions, entail significant modeling. I am thus very interested in developing chemical proxies for the concentration of major ions in seawater. For example, a proxy for the concentration of seawater sulfate may allow researchers to distinguish among competing explanations for rapid changes in the sulfur isotope ratio of barite throughout the Cenozoic. Similarly, establishing constraints on the concentration of calcium and magnesium through time could provide insight into Phanerozoic transitions between calcite and aragonite seas.

The study of stable isotope ratios is fundamentally limited by which nuclides exist. For example, while oceanographers would like to study glacial-interglacial variability in phosphorus isotopes or igneous petrologists may wish they could measure the stable isotope ratios of sodium and aluminum, all three of these elemental systems are monoisotopic. However, 23-Na, 27-Al, and 31-P all have isotones, which are nuclides with the same number of neutrons but different numbers of protons. For example, 22-Ne, 23-Na, and 24-Mg all have twelve neutrons but different numbers of protons. I am interested in whether the relative abundances of isotones within natural materials may be able to shed light into problems hindered by the lack of stable isotopes. There are immediate conceptual difficulties with this idea, chief among them accounting for the different chemistries of the nuclides, as well as major analytical hurdles to overcome.