My research interests encompass many fields in Earth System Science including geology, biogeochemistry, as well as some atmospheric and ocean science. I am currently investigating the geologic cycling of nitrogen, both over long time scales and focusing on interesting time periods in Earth history. Other interests include delivery of volatiles to Earth during accretion and subsequent cycling, evolution of the atmosphere, and development of the continental crust.
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Paleoarchean seawater chemistry: For my postdoctoral work, I will be using the Panorama VMS district in Australia as a repository of geochemical information about the Paleoarchean ocean. The Paleoarchean is a key transition time in Earth history, with the appearance of a more complete and regular geologic record, and several major metabolisms including nitrogen-fixation. Using the altered oceanic crust exposed at Panorama, in conjunction with inverse modelling, I hope to decipher the oxyen-, nitrogen-, and sulfur-isotopic composition of the seawater as well as the Fe/S ratio of the crust. From these, I aim to describe the temperature of ancient seawater, the cycling of nutrients by organisms, and investigate the depth of the ocean in this interesting time.
Geologic Nitrogen Cycle: Long considered to be a noble element residing primarily in the atmosphere, over the last 10-20 years a new, more dynamic interpretation of the links between the atmosphere, biosphere, and geosphere. I am investigating this fascinating cycle in two ways:
I am constructing an Earth system box model to investigate the movement of N over Earth history. This model will incorporate both geologic and biologic cycling of N. Important fluxes include N fixing and denitrification in the ocean, incorporation into crust during hydrothermal alteration, and volatilization during subduction.
I have measured the N contents of a series of glacial tills spanning the last 3 Ga of Earth history as a proxy for the N evolution of the continental crust. Our results show that the N content has increased over time, hinting at a sequestration of atmospheric N into the geosphere.
Nitrogen cycling during Snowball Earth: I am interested in nutrient cycling during Neoproterozoic Snowball Earth events. Biologic N cycling leaves distinctive isotopic signatures in sediments, and I am investigating the composition of sub-glacial deposits from Namibia.
Modern geologic and biologic nitrogen cycle of the Earth. Geologic and biologic nitrogen fluxes and reservoir sizes are shown. The biologic fluxes are large, while the geologic fluxes are relatively small, similar to the carbon cycle.
Publications. Johnson, Benjamin W.,Poulton, Simon F., and Goldblatt, Colin. accepted. Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth. Nature Communications.
Johnson, Benjamin W. and Goldblatt, Colin. 2017. A secular increase in continental crust nitrogen during the Precambrian. Geochemical Perspectives Letters, 4:24-28.PDFLink
Johnson, Benjamin W., Drage, Natashia, Spence, Jody, Hanson, Nova, El-Sabaawi, Rana, and Goldblatt, Colin. 2017. Measurement of geologic N using mass spectrometry, colourimetry, and a newly adapted fluorometry technique. Solid Earth, 8(2):307– 318. PDFLink
Hoffman, P. F., Bellefroid, E. J., Hodgin, E., Hodgkiss, M., Johnson, Benjamin W., and Lobiance, S. (Accepted). Sedimentary depocenters on Snowball Earth: case studies from the Sturtian Chuos Formation in nothern Namibia. Geosphere Stüeken, E., Kipp, M., Koehler, M., Schwieterman, E., Johnson, Benjamin W, and Buick, R. (2016). Modeling pN2 through geologic time: Implications for atmospheric biosignatures. Astrobiology, 16(12), 949-963. Link
Hoffman, Paul F.; Bellegroid, Eric J.; Johnson, Benjamin W.; Hodgskiss, Malcolm S.W.; Schrag, Daniel P. and Halverson, Galen P. 2016. Early extensional detachments in a contractional orogen: coherent, map-scale, submarine slides (mass transport complexes) on the outer slope of an Ediacaran collisional foredeep, eastern Kaoko belt, Namibia. Canadian Journal of Earth Sciences. 53, 1-13. PDFLink Johnson, Benjamin W. and Goldblatt, Colin. 2015. The Nitrogen Budget of Earth. Earth Science Reviews, 148, 150-173PDFLink
Schauer, Andrew J.; Kunasek, Shelley A.; Sofen, Eric D.; Erbland; Joseph, Savarino, Joel; Johnson, Ben W., Amos, Helen M.; Shaheen, Robina; Abaunza, Mariana; Jackson, Terri L.; Thiemens, Mark H. and Alexander, Becky. 2012. Oxygen isotope exchange with quartz during pyrolosis of silver sulfate and silver nitrate. Rapid Communications in Mass Spectrometry, 26, 2151-2157. PDF
Measurement of geologic NH4+: We are adapting a fluorometric technique, common in aquatic sciences, for use in quantifying geologic NH4+ concentrations. The goal of this research is to establish a relatively quick and easy way to analyze this difficult to measure species in rocks and minerals. PDFLink
The Nitrogen Budget of Earth: This project compiled and comprehensively synthesized the published record of N analyses in geologic materials. Based on these analyses, in conjunction with N-Ar systematics in basalts and xenoliths, we show that the majority of N in the Earth is contained in the mantle. This work also calculates a N budget based on comparison to chondrites, and estimates both a core N content and discusses using the moon as an analog for the early Earth mantle. This work has is published in Earth Science Reviews, and is posted to arXiv.
Development of Oxygen Isotope analysis in sulfate:
Thermal and isotopic history of a small granodiorite pluton:
Oxygen and carbon isotopic investigation of a dinosaur fossil site: