My research interests encompass many fields in Earth System Science including geology, biogeochemistry, as well as some atmospheric and ocean science. I am interested in deep-time, whole Earth element cycles and the history of the combined atmosphere-biosphere-geosphere system. I use analytical and stable isotope geochemistry, linked with geologic field work and modeling, to investigate these large scale questions.
Current Projects. 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.
Glacials through time: I am interested in how the biosphere and climate react and respond to glacial periods throughout Earth history. My current focus is on the nitrogen cycle and redox state of the ocean during the Neoproterozoic Snowball Earth and characterizing the oldest glacial rocks on Earth. For the first project, I have measured samples from Namibia, and found the presence of an active nitrogen cycle and aerobic ocean during the Marinoan. This is difficult to reconcile with a so-called "hard Snowball'', or totally ice-covered ocean. I am continuing to test this hypothesis by collecting and analyzing samples from other locations, including the Mineral Fork Tillite in Utah.
Recently, I have become interested in a diamictite below the Stillwater Complex in Montana, which may represent the oldest glacial rocks on Earth. These rocks were interpreted as glacial in the 1970s, with alternate ideas posed in the 1980s, but never conclusively characterized. Additionally, a zircon age from this same period suggests the unit is 2.7 to 3.1 Ga, but it's possible it may be older still, since this age could be an average of detrital and metamorphic zircons. I have collected samples from the area for new zircon age determination, and will continue to study the sedimentary structures in outcrop to assess its potential glaciogenic origin.
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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. 2019 Johnson, Benjamin W. and Wing, Boswell. under review. Altered ocean crust reveals an 18O-enriched early Archean ocean. Nature Geoscience.
2018 Johnson, Benjamin W. and Goldblatt, Colin. 2018. EarthN: A new Earth System Nitrogen Model. Geochemistry, Geophysics, Geosystems. 1-27. ArXiV, PDF, Link
2017 Johnson, Benjamin W.,Poulton, Simon F., and Goldblatt, Colin. 2017. Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth. Nature Communications. 8:1316PDFLink
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
2016 Hoffman, P. F., Bellefroid, E. J., Hodgin, E., Hodgkiss, M., Johnson, Benjamin W., and Lobiance, S. (2016). Sedimentary depocenters on Snowball Earth: case studies from the Sturtian Chuos Formation in nothern Namibia. Geosphere. 13(3), 811-837. PDFLink
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. PDFLink
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 2015 Johnson, Benjamin W. and Goldblatt, Colin. 2015. The Nitrogen Budget of Earth. Earth Science Reviews, 148, 150-173PDFLink
2012 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: