Bishop_cropJulie Bowles's Research

Most of my research centers around the field of paleomagnetism—the study of Earth’s magnetic field as recorded in rocks and sediments. My work can be subdivide into three main areas: understanding how Earth’s magnetic field has changed over time; using these "rock records" of changing magnetic fields and magnetic properties to interpret volcanic processes; and understanding how and how well magnetic minerals record the field.

How does the Earth’s magnetic field change over time?

Earth's magnetic field varies in both space and time. Characterizing and understanding those variations can help us to understand the processes in Earth's core that generate the magnetic field. They can also help to provide constraints on planetary differentiation, inner core nucleation, and atmospheric evolution. Records of the Earth's field can be found in rocks, marine and lake sediments, and fired archeological artifacts. Current work in this area involves using volcanic glass from the Juan de Fuca Ridge to better constrain field variations over the past few tens of thousands of years, and evaluating ignimbrites and other pyroclastic flows as potential field recorders over longer timescales.

river_crossing2_cropUsing paleomagnetic records to interpret volcanic and other Earth processes

By comparing records of the Earth's field recorded in igneous rocks with known variations in in the field, we can place some age constraints on lava flows or estimate whether or not two flows were likely erupted at the same time. Additionally, by studying the orientation of magnetic minerals in some igneous rocks like ignimbrites, we can learn something about flow direction and source location. Identifying stratigraphic changes in the polarity of the Earth's magnetic field (i.e., magnetostratigraphy) has long been used to date both sedimentary and volcanic sequences, and the resulting age constraints can be used to better understand many Earth processes like paleoclimate change. Ongoing work in this area includes examining eruption timing and recurrence intervals on the Juan de Fuca Ridge (in collaboration with Brian Dreyer, UC Santa Cruz) and the Galapagos Spreading Center (in collaboration with John Sinton and Ken Rubin, Univ. Hawaii; and Scott White, Univ. of South Carolina); and examining flow direction and post-emplacement rotations in pyroclastic flows (in collaboration with Jeff Gee at Scripps Institution of Oceanography and Mike Jackson at Univ. of Minnesota).

Alvin_cropHow do magnetic minerals form and acquire magnetization?

We use paleomagnetic data to provide constraints on tectonic reconstructions, geodynamo formation and behavior, planetary evolution, magmatic flow, and sub-solidus deformation. To reliably draw these kinds of conclusions, it is necessary to fully understand the mechanisms by which magnetic minerals form and acquire magnetization and the temperature at which this happens. How reliable are our paleomagnetic recorders? Recent work in this area has involved creating synthetic Mars rocks to better understand the strong magnetic anomalies on Mars (collaboration with Julia Hammer, Univ. Hawaii, and Stefanie Brachfeld, Montclair State University); and creating synthetic basaltic glass to understand the timing of magnetite formation in submarine eruptions and its implications for the type of magnetization they acquire (collaboration with Jeff Gee, Scripps Institution of Oceanography, and Reid Cooper, Brown University).

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